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Stability balls, balance boards and similar devices are sold on the idea that an unstable surface makes each exercise harder for the core and stabilising muscles. Three published reviews have examined this idea, which the literature calls instability resistance training. This article summarises what they report about muscle activation, force output and trunk stability, and where the evidence remains unsettled. It covers general findings on healthy people and is not advice for anyone with an injury or health condition. None of the three abstracts reports a pooled meta-analytic effect size, so the findings are described as reviews of the literature.

What is being compared

Behm and Colado (Sports Health, 2013) define instability resistance training as the use of unstable surfaces and devices to strengthen the core or trunk muscles, and describe it as popular in fitness facilities. In practice the devices include stability balls and balance boards, and the comparison is with the same exercise on a stable surface. The three reviews come from different years: Behm and Anderson in 2006, Behm and Colado in 2013 and Zemkov in 2017.

Muscle activation is higher, force output is lower

Behm and Anderson (Journal of Strength and Conditioning Research, 2006) report that instability can decrease the externally measured force output of a muscle while maintaining high muscle activation, and attribute the high activation of limbs and trunk to increased stabilisation functions. Zemkov (Journal of Traditional and Complementary Medicine, 2017) reports that electromyography studies show significantly greater activity of trunk-stabilising muscles during exercises under unstable than stable conditions, and that it has been established that peak isometric force and rate of force development are significantly lower under unstable conditions. Power output was also compromised on unstable surfaces, though Zemkov notes this depends on the type of exercise, the device, the weight lifted and the person’s training background.

Effects on trunk stability and strength gains

Zemkov reports that intervention studies show a greater improvement in trunk stability after programmes using unstable devices than after floor exercises, and interprets this as instability training facilitating neural adaptation of trunk-stabilising muscles. He adds that both acute and long-term responses of the primarily activated muscles to exercises on unstable surfaces remain a matter of debate.

Behm and Anderson state that the lower force output may be detrimental to absolute strength gains. They report that some studies found increased co-contractions with unstable training, and that the positive effects of instability resistance training on sports performance had yet to be quantified. Behm and Colado report that studies document adaptations similar to stable resistance training in recreationally active individuals, and that similar progressions with lower resistance may improve balance and stability, increase core activation and improve motor control. They also note contradictory recommendations across the literature.

What the three reviews agree on

• Unstable conditions raise the activity of stabilising muscles.
• Unstable conditions lower the force or power a person can produce with the same exercise, so the loads used are typically lower.
• Recommendations differ on how useful the approach is, and the effect on sports performance was not established.
• Behm and Anderson conclude that a resistance programme aimed at musculoskeletal health should include both stable exercises, which emphasise higher force, and unstable ones, which emphasise balance stress.

Reading the evidence with care

Higher stabiliser activity does not by itself show a better training result. The reviews describe measurements of activation and intervention studies, and they contain no head-to-head comparison of specific products, such as one type of balance board against another. They also do not address the cost or space cost of a device. Findings from recreationally active adults should not be assumed for beginners or for athletes.

The lower force output has a practical consequence for loading. If the aim is to train the legs or chest with heavy weights, the reviews suggest unstable surfaces reduce the load that can be lifted, which is why the authors advise combining stable and unstable work. This site’s article on free weights against machines covers a related question about stabiliser demand.

Where equipment enters

Buying decisions can be framed by these findings without going beyond them. A device designed to add instability is relevant to a goal such as trunk stability or balance practice, and less relevant to a goal of lifting as heavy as possible. The article on mobility and balance equipment for home use compares this kind of kit as a product category.

Frequently asked questions

Do unstable surfaces build more core strength?

Zemkov reports greater activity of trunk-stabilising muscles and greater improvement in trunk stability compared with floor exercises, though he describes the responses of the main muscles as debated.

Can heavy lifting be done on an unstable surface?

The reviews report lower peak force and power on unstable surfaces, so lower loads are typically used.

The bottom line

Three reviews indicate that unstable devices increase stabiliser activity and trunk stability while lowering force and power output, which limits their usefulness for maximal strength. Recommendations in the literature differ and a benefit for sports performance was not established. The reviews support unstable work as an addition to, not a replacement for, stable exercises, and they do not compare individual products.

Sources

• Behm DG, Anderson KG, “The role of instability with resistance training”, Journal of Strength and Conditioning Research, 2006
• Behm DG, Colado JC, “Instability resistance training across the exercise continuum”, Sports Health, 2013
• Zemkov E, “Instability resistance training for health and performance”, Journal of Traditional and Complementary Medicine, 2017

A bench and a loaded barbell are among the larger purchases in a home gym, and push-ups need neither. Three published trials have compared push-up training with bench press training directly. This article reports what each found, how they matched the load between the exercises, and why the results cannot be stretched into a general verdict. It covers general findings in healthy adults and is not advice for anyone with an injury or health condition. No pooled analysis of these trials is cited here, since the sources are three separate small studies.

Trial one: bench press against elastic-band push-ups in experienced trainees

Calatayud and colleagues (Journal of Strength and Conditioning Research, 2015) first measured muscle activity by electromyography (EMG) during a six-repetition-maximum (6RM) bench press and a push-up with an elastic band adding resistance. At baseline the EMG amplitude showed no significant difference between the two. Thirty university students with advanced resistance training experience were then randomly allocated to a 6RM bench press group, a 6RM elastic-band push-up group or a control group for five weeks, using the same loads as in the EMG measurements.

Both training groups improved their 1RM and 6RM significantly and by similar amounts, while the control group did not change. The authors conclude that when EMG values are comparable and conditions are reproduced, the two exercises can provide similar strength gains.

Trial two: low-load bench press against load-matched push-ups

Kikuchi and Nakazato (Journal of Exercise Science and Fitness, 2017) recruited 18 men aged 19 to 22 and randomly assigned them to bench press at 40% of one-repetition maximum or to push-ups with the position adjusted, for example kneeling, to match the same load. Both groups trained twice a week for eight weeks.

The authors report significant increases in 1RM and in muscle thickness of the triceps and the pectoralis major in both groups. Biceps thickness increased significantly only in the bench press group. Medicine-ball throw power and the maximum-repetition test showed no significant change in either group, and the change in muscle thickness did not differ significantly between the groups. The authors conclude that push-ups at a load similar to 40% of 1RM bench press are comparably effective for hypertrophy and strength over eight weeks. They also note that push-up intensity can be altered with variations such as bent knees or hand and foot elevation, and raised further using an elastic band or a weight plate on the back.

Trial three: progressive calisthenic push-ups against bench press

Kotarsky, Christensen, Miller and Hackney (Journal of Strength and Conditioning Research, 2018) studied 23 healthy, moderately trained men, randomly assigned to a progressive push-up group (n = 14) or a bench press group (n = 9), training three days a week for four weeks. They measured muscle thickness, a seated medicine ball put, bench press 1RM and a push-up progression. The abstract reports significant increases in 1RM, and the authors describe the study as the first to show that calisthenics, using progressive variations to maintain programming variables, can improve upper-body muscle strength.

What the trials have in common

• All were short (four to eight weeks) and small, with between 18 and 30 participants in total. Two explicitly enrolled men, and the abstract of the third does not state participants’ sex.
• All matched load between the exercises by design, through EMG matching, a fixed percentage of 1RM or progressive variations. Push-ups performed at whatever load a person happens to choose were not tested.
• All reported comparable strength improvement between push-up and bench press training.
• Kikuchi and Nakazato is the only one of the three whose abstract reports thickness at several sites, and it found a difference at the biceps that favoured the bench press group.

What the trials cannot show

None of the trials followed participants for longer than eight weeks, so they say nothing about long-term progress once a person can do many push-ups with a body weight that cannot easily be increased. Kikuchi and Nakazato themselves note that further studies are needed in highly trained subjects. The trials are also small enough that the absence of a significant difference between groups is not proof of equivalence. Findings in the male participants cannot be assumed for women, and none of the abstracts reports separate results for women.

The trials do not compare cost, space or convenience. They say nothing about the range of exercises a bench and barbell make possible, such as heavy loading of the chest at higher intensities. Kikuchi and Nakazato state that push-ups can be loaded further with a band or plate, which means some equipment can still be relevant to push-up training.

What this means for a buying decision

The evidence supports a narrow conclusion: in short trials with matched loads, push-up variations produced upper-body strength gains and pectoral and triceps thickness gains similar to bench press training. It does not show that push-ups replace the bench press for someone seeking to lift heavy loads, or that a bench is unnecessary. For readers weighing this against other options, related articles on this site cover resistance bands and suspension trainers as equipment substitutes and weight benches.

Frequently asked questions

Can push-ups build the same strength as the bench press?

In these three trials, with matched loads and short durations in male participants, both exercises improved bench press strength by similar amounts.

Do push-ups build the biceps?

In the trial that measured it, biceps thickness increased significantly only in the bench press group.

The bottom line

Three small randomised trials found that push-up training and bench press training, at matched loads, produced similar strength gains and similar gains in chest and triceps thickness over four to eight weeks. They were short, small, mostly in men, and did not test push-ups at self-selected loads, so they support cautious substitution and not a general claim that push-ups make a bench unnecessary.

Sources

• Calatayud J, Borreani S, Colado JC, Martin F, Tella V, Andersen LL, “Bench press and push-up at comparable levels of muscle activity results in similar strength gains”, Journal of Strength and Conditioning Research, 2015
• Kikuchi N, Nakazato K, “Low-load bench press and push-up induce similar muscle hypertrophy and strength gain”, Journal of Exercise Science and Fitness, 2017
• Kotarsky CJ, Christensen BK, Miller JS, Hackney KJ, “Effect of Progressive Calisthenic Push-up Training on Muscle Strength and Thickness”, Journal of Strength and Conditioning Research, 2018

Isometric training means producing force without the muscle changing length. Two 2019 reviews summarise what is known about its long-term effects. This article reports what each says, notes how their methods differ, and identifies what remains uncertain. It covers general findings on training in healthy people and is not advice for anyone with an injury or health condition.

Two different kinds of review

The reviews are not equivalent in strength of evidence. Oranchuk, Storey, Nelson and Cronin (Scandinavian Journal of Medicine and Science in Sports) conducted a systematic review of medium- to long-term adaptations, searching MEDLINE, PubMed, SPORTDiscus and CINAHL. It included 26 research outputs of at least three weeks. Lum and Barbosa (International Journal of Sports Medicine) describe their paper as a brief review with a narrative summary of findings on isometric strength training and its effects on strength and dynamic performance. A narrative summary does not pool results statistically, so its training figures are the authors’ synthesis and not a measured optimum.

Muscle length: the systematic review’s clearest signal

Oranchuk and colleagues report that isometric training at longer muscle lengths produced greater muscular hypertrophy than equal volumes of training at shorter muscle lengths. The figures they give are weekly gains of 0.86 to 1.69% at longer lengths, against 0.08 to 0.83% at shorter lengths. They also report that long-muscle-length training resulted in greater transference to dynamic performance. The review says relatively few studies met its inclusion criteria, so these figures come from a small evidence base.

Intensity and intent

The systematic review reports several other findings:

• ballistic intent, meaning trying to produce force as quickly as possible, gave greater neuromuscular activation and greater rapid force production than non-ballistic intent, for example weekly gains in rapid force production of 1.2 to 13.4% against 1.01 to 8.13%;
• substantial improvements in muscular hypertrophy and maximal force production were reported regardless of training intensity;
• high-intensity contractions, at about 70%, were required to improve tendon structure and function.

The intensity result is worth reading carefully: it says intensity was not critical for hypertrophy or maximal force in the included studies, while the tendon finding is specific to the tendon outcome measured.

Practical figures from the narrative review

Lum and Barbosa state that isometric training has been shown to induce less fatigue and to give superior joint-angle-specific strength compared with dynamic strength training, and to benefit sports-related dynamic performance such as running, jumping and cycling. Their suggested parameters are:

• To increase muscle hypertrophy: contractions at 70 to 75% of maximum voluntary contraction, held for 3 to 30 seconds per repetition, with a total contraction duration of more than 80 to 150 seconds per session, for more than 36 sessions;
• To increase maximum strength: contractions at 80 to 100% of maximum voluntary contraction, held for 1 to 5 seconds, with total contraction time of 30 to 90 seconds per session, using multiple joint angles or a targeted angle;
• To improve rate of force development: performing the contractions in a ballistic manner.

Because the two reviews are different kinds of evidence, the second set of figures should be read as the authors’ summary of the literature and not as prescriptions tested against one another. The two reviews agree on a general direction: ballistic intent helps rapid force production, and the joint angle used matters.

What the reviews do not say about equipment

Neither review evaluates products, and neither compares isometric holds against dynamic training as an equipment strategy. Any suggestion that isometric work saves money or space is outside what these papers show. The reviews are relevant mainly as a guide to how isometric sessions might be structured for someone who already has an anchor point or a loaded position to hold against. For readers comparing isometric holds with lifting through a range of motion, the related article on this site about full against partial repetitions covers a neighbouring question.

Limits of the evidence

• The systematic review found relatively few studies, so its hypertrophy and transfer figures rest on small numbers.
• The narrative review does not pool data and its parameter ranges are wide.
• Both concern healthy training populations and neither replaces individual medical or coaching advice.
• Comparisons of isometric training with dynamic training on equal terms are limited in these papers, which is why they do not support claims that one is superior.

Frequently asked questions

Does isometric training build muscle?

The systematic review reports substantial improvements in muscular hypertrophy across the included studies, with larger gains at longer muscle lengths.

Does the joint angle matter?

Both reviews indicate it does: the systematic review found greater hypertrophy and transfer at longer muscle lengths, and the narrative review recommends multiple or targeted joint angles for maximum strength.

The bottom line

Two 2019 reviews indicate that isometric training can produce meaningful gains in size and force, that longer muscle lengths appear to favour hypertrophy and transfer, and that ballistic intent favours rapid force production. The systematic review is based on 26 research outputs and the narrative review supplies broad, non-pooled parameter ranges. Neither compares products or establishes that isometric work is better than dynamic training.

Sources

• Oranchuk DJ, Storey AG, Nelson AR, Cronin JB, “Isometric training and long-term adaptations: Effects of muscle length, intensity, and intent: A systematic review”, Scandinavian Journal of Medicine and Science in Sports, 2019
• Lum D, Barbosa TM, “Brief Review: Effects of Isometric Strength Training on Strength and Dynamic Performance”, International Journal of Sports Medicine, 2019

Home training removes many scheduling limits, so the question of whether to train in the morning or the evening is a practical one. Two published reviews address it directly: a 2019 systematic review with meta-analysis of resistance training studies, and a 2012 review of training at a specific time of day. This article summarises what each reports and what the evidence does not settle. It covers general findings in healthy adults and is not advice for anyone with a health condition.

The 2019 systematic review and meta-analysis

Grgic, Lazinica, Garofolini, Schoenfeld, Saner and Mikulic searched PubMed/MEDLINE, Scopus and SPORTDiscus for studies of time-of-day-specific resistance training. To be included, a study had to equate other training variables, such as frequency and volume, between the groups, so that time of day was the difference being tested. Eleven studies of moderate and good methodological quality were included, assessed with the Downs and Black checklist.

The authors report five main findings:

• at baseline, strength is significantly greater in the evening than in the morning;
• training in the morning may raise strength measured in the morning to levels similar to those measured in the evening;
• training in the evening maintains the general difference across the day, with greater strength in the evening;
• when morning and evening training groups are compared, increases in strength are similar in both, whatever time of day the strength test is done;
• increases in muscle size are similar regardless of the time of day at which training is performed.

What the 2012 review adds

Chtourou and Souissi reviewed performance after training at a specific time of day. They report that the effect of time of day on aerobic performance appears to be equivocal, while for anaerobic exercise the effect is well established, with early-morning lows and peak performance in the late afternoon. Regular training in the morning may raise the lower morning performances to the same or even a higher level than the usual late-afternoon peak, through a greater increase in evening performance. Regular evening training may widen the morning-to-evening difference through a greater increase in late-afternoon performance. The authors conclude that adaptations to training are greater at the time of day at which training is regularly performed than at other times. They add that changes in resting hormone concentrations could explain the time-of-day-specific adaptations, but that precise information on the underlying mechanisms is lacking.

Putting the two reviews together

The two reviews describe a consistent picture. Performance tends to vary across the day, with lower values in the early morning and higher values later. The body appears to adapt to the time at which it is trained, which is why morning training narrows the gap. Yet the 2019 meta-analysis, which isolates time of day by equating other variables, finds similar gains in strength and similar increases in muscle size whichever time of day is used. The specificity effect therefore affects how strength presents at a given hour more than the total amount gained.

What this means for testing and tracking

One practical implication follows directly from the reported findings. Strength is measured higher in the evening than in the morning at baseline, and training at a given time raises performance at that time. Comparing a morning test with an evening test can therefore mix a genuine change in strength with a time-of-day difference. Tests of maximum lifts, and the loads used to set progression, are more informative when repeated at a consistent time. This is relevant to any schedule that uses one-repetition-maximum estimates, covered on this site in One-Rep Max Testing and Percentage-Based Training.

Limits of the evidence

• The 2019 review includes only 11 studies, so subgroup comparisons rest on small numbers.
• The 2012 review does not report a pooled analysis in its abstract and states that mechanisms are unknown.
• The reviews cover time-of-day effects on average, not individual chronotype. Neither abstract reports results for early-riser and late-riser groups separately.
• The findings concern strength and muscle size. They do not address other goals such as sleep, adherence or aerobic performance, for which the 2012 review notes that the evidence on time of day is equivocal.

Where equipment enters

These reviews say nothing about products. Their relevance to buying is indirect: a home setup that can be used at the same time every day, or at whichever time fits a household, makes it easier to hold training time constant. Choices that affect when a machine can be used, such as noise, are treated in articles on this site about treadmill noise and vibration in upstairs rooms.

Frequently asked questions

Is evening training better for strength?

The 2019 meta-analysis finds similar strength gains from morning and evening training. Strength is higher in the evening at baseline, but the gains from training do not differ between the two groups.

Does the time of day matter for muscle growth?

According to the same review, increases in muscle size are similar irrespective of when training is done.

The bottom line

Reviews of time-of-day training find that strength tends to be higher in the evening, that the body adapts to the time it is trained, and that morning and evening training deliver similar gains in strength and muscle size when other variables are equal. The best time is therefore the one that can be kept consistent, and tests are most comparable when repeated at the same hour. The evidence base is small and does not address individual differences.

Sources

• Grgic J, Lazinica B, Garofolini A, Schoenfeld BJ, Saner NJ, Mikulic P, “The effects of time of day-specific resistance training on adaptations in skeletal muscle hypertrophy and muscle strength: A systematic review and meta-analysis”, Chronobiology International, 2019
• Chtourou H, Souissi N, “The effect of training at a specific time of day: a review”, Journal of Strength and Conditioning Research, 2012

Whether each set should be pushed until no further repetition can be completed is one of the most argued questions in home training. Three published systematic reviews with meta-analysis have compared training to failure with training that stops short. This article summarises what each reports and where the evidence stops. It covers general findings about resistance training in healthy adults and is not advice for anyone with an injury or health condition.

Why the definition matters

The reviews do not use one definition. The 2023 review by Refalo and colleagues separates momentary muscular failure from “set failure”, which it defines as anything other than momentary muscular failure, because the included studies used different definitions of failure. It also compares training to different velocity loss thresholds. A finding about one definition cannot be assumed to hold for another.

Strength: the 2016 meta-analysis

Davies, Orr, Halaki and Hackett pooled eight studies comparing failure with non-failure training for strength. Four controlled training volume and four did not. The main results were:

• non-failure training produced a 0.6 to 1.3% greater strength increase, with a small pooled effect favouring non-failure training (effect size 0.34, p = 0.02);
• small effects favouring non-failure training were also found for compound exercises (0.37 to 0.38) and for trained participants (0.37);
• in the four volume-controlled studies there was no significant effect, although the trend favoured non-failure training;
• the methodological quality of the included studies was rated as moderate.

The authors conclude that the small percentage improvement is unlikely to be meaningful, so similar strength gains appear achievable with or without failure. They add that it seems unnecessary to train to failure to maximise strength and suggest that, if it is used, it should be used sparingly to limit the risks of injury and overtraining.

Strength and size: the 2022 meta-analysis

Grgic, Schoenfeld, Orazem and Sabol included 15 studies, all in young adults. The results were:

• no significant difference between training conditions for strength (effect size -0.09, 95% confidence interval -0.22 to 0.05) or for hypertrophy (0.22, 95% confidence interval -0.11 to 0.55);
• in studies that did not equate training volume, a significant effect favouring non-failure training on strength (-0.32, confidence interval -0.57 to -0.07);
• in resistance-trained participants, a significant effect favouring training to failure for hypertrophy (0.15, confidence interval 0.03 to 0.26).

The authors conclude that training to muscle failure does not seem to be required for gains in strength and muscle size, but does not seem to have detrimental effects on these adaptations either. They call for more studies among older adults and highly trained individuals.

Muscle size: the 2023 meta-analysis

Refalo, Helms, Trexler, Hamilton and Fyfe pooled 15 studies that measured hypertrophy in healthy adults of any age or training experience. They report:

• a trivial advantage for training to set failure over non-failure (effect size 0.19, 95% confidence interval 0.00 to 0.37, p = 0.045), with no moderating effect of volume load or relative load;
• no advantage for momentary muscular failure over non-failure (0.12, confidence interval -0.13 to 0.37, p = 0.343);
• no advantage for higher over moderate velocity loss thresholds (0.08, confidence interval -0.16 to 0.32, p = 0.529).

The authors conclude there is no evidence that momentary muscular failure is superior to non-failure training for hypertrophy, and that closer proximity to failure does not always produce more growth. They suggest a possible non-linear relationship between proximity to failure and hypertrophy.

Reading the three reviews together

The reviews point the same way. For strength, neither of the two analyses that measured it finds a benefit for failure, and the 2016 analysis leans slightly towards stopping short. For muscle size, the effects near zero are small: the 2022 review reports a benefit for training to failure only in the resistance-trained subgroup, and the 2023 review reports a trivial advantage under a broad definition of set failure that disappears for momentary failure. The confidence intervals in several results touch or cross zero, so these findings describe averages across studies and not a rule for any individual.

Limits apply to all three. The studies in the 2022 review were all in young adults, and that review calls for more work in older adults and highly trained people. The numbers of trials are modest, at 8 to 15 per review, and protocols differ. None of them can say how stopping short, by a fixed number of repetitions or by an effort rating, should be prescribed. That question is covered on this site in RPE and RIR: Using Perceived Effort to Set Your Training Load.

Where equipment enters

These reviews do not evaluate products. Equipment matters in a practical sense: going close to failure with a loaded barbell is easier to do safely where the setup includes pins, straps or spotter arms, which are compared in Safety Systems on Racks. Stopping short of failure reduces how often that hardware is needed, and the reviews suggest little is lost in doing so on average.

Frequently asked questions

Does training to failure build more muscle?

Across the 2022 and 2023 meta-analyses, the average difference in muscle size is small and often not statistically significant. The 2022 review found an advantage for failure among resistance-trained participants.

Is it harmful to train to failure?

The 2022 authors report that training to failure does not seem to have detrimental effects on strength and size adaptations. The 2016 authors suggest using it sparingly to limit injury and overtraining risk, which is a suggestion and not a finding of the pooled data.

The bottom line

Three meta-analyses find that stopping short of failure produces, on average, similar strength gains (two analyses) and similar or slightly lower muscle growth (two analyses) than training to failure, with a possible small edge for failure among trained lifters in one review. None supports treating failure as a requirement. The trials pooled are modest in number, one review covers only young adults, and none can dictate an exact number of repetitions to leave in reserve.

Sources

• Davies T, Orr R, Halaki M, Hackett D, “Effect of Training Leading to Repetition Failure on Muscular Strength: A Systematic Review and Meta-Analysis”, Sports Medicine, 2016
• Grgic J, Schoenfeld BJ, Orazem J, Sabol F, “Effects of resistance training performed to repetition failure or non-failure on muscular strength and hypertrophy: A systematic review and meta-analysis”, Journal of Sport and Health Science, 2022
• Refalo MC, Helms ER, Trexler ET, Hamilton DL, Fyfe JJ, “Influence of Resistance Training Proximity-to-Failure on Skeletal Muscle Hypertrophy: A Systematic Review with Meta-analysis”, Sports Medicine, 2023

Anyone equipping a home setup with both a cardio machine and weights has to decide how the two fit together in a week. The research question is known as concurrent training: does adding aerobic work interfere with strength and muscle gains? Several meta-analyses have pooled the trials. This article summarises three, covering overall compatibility, session order and high-intensity interval training. The findings apply to healthy adults in the studies and do not amount to advice for people with injuries or medical conditions.

Overall compatibility: the 2022 meta-analysis

Schumann and colleagues included 43 studies that compared supervised concurrent aerobic and strength training, lasting at least four weeks, against an identical strength programme with no aerobic training. The pooled results were:

• Maximal strength: a standardised mean difference of -0.06 (95% confidence interval -0.20 to 0.09; P = 0.446), meaning no significant difference;
• Muscle hypertrophy: -0.01 (confidence interval -0.16 to 0.18; P = 0.919), again no significant difference;
• Explosive strength: -0.28 (confidence interval -0.48 to -0.08; P = 0.007), a significant reduction with concurrent training.

The authors conclude that concurrent training does not compromise muscle hypertrophy or maximal strength, but that explosive strength gains may be attenuated. The attenuation was more pronounced when both kinds of training were done in the same session (P = 0.043) than when sessions were separated by at least three hours (not significant). No significant effects were found for the type of aerobic training (cycling against running), the frequency of concurrent training (more or fewer than five weekly sessions), training status (untrained or active) or mean age (under or over 40).

For a lifter focused on muscle size and maximal strength, the meta-analysis found no significant cost from adding cardio. The included trials were supervised programmes.

Which goes first in the same session?

A 2018 systematic review and meta-analysis looked only at trials that compared strength before endurance with endurance before strength within the same session. Lower-body one-repetition maximum was significantly higher when strength training came first, with a pooled mean change of 3.96 kg (95% confidence interval 0.81 to 7.10 kg). The order made no difference to maximal aerobic capacity (pooled difference 0.39 ml per kg per minute, confidence interval -1.03 to 1.81). The authors conclude that putting strength first appears beneficial for lower-body strength while aerobic improvement is unaffected by order. The absolute difference is small and the interval wide, so it is a modest edge and not a rule.

Interval training and lower-body strength

A separate 2018 meta-analysis compared concurrent high-intensity interval training (HIIT) plus resistance training with resistance training alone. Muscle hypertrophy and upper-body strength changed similarly. Lower-body strength increased less with the combination (effect size -0.248, P = 0.049). Sub-analyses showed a trend, not statistically significant, for cycling HIIT to have a more negative effect on lower-body strength (-0.377, P = 0.074) than running HIIT (-0.176, P = 0.261). The authors suggest that any negative effect on lower-body strength may be reduced by using running-based HIIT and longer rest between the two modes, but they present this as a possibility. The 2022 meta-analysis, by contrast, found no significant difference between cycling and running for the overall outcomes, so the modality point remains unresolved.

Reading the evidence

• Consistent: hypertrophy and maximal strength held up under concurrent training in the 2022 pooled analysis.
• Some signal, some uncertainty: explosive strength and lower-body strength showed reductions in one or both analyses, with same-session training and cycling HIIT the suggested aggravating factors.
• Unresolved: the cycling against running contrast, since one analysis found a non-significant trend and the other found no significant moderator effect.
• Population: healthy adults in supervised trials. Extrapolating to home routines, older or clinical populations or elite athletes goes beyond what the reviews tested.

Turning it into a weekly plan

The reviews do not prescribe schedules, but they support some options. If explosive strength is not a priority, cardio and strength can be combined in one session without expecting a large penalty to muscle size or maximal strength. If it is, or if lower-body strength is a particular goal, separating sessions by several hours, doing strength first or choosing running-style intervals over cycling are the variations the analyses point to. Equipment placement can follow whichever schedule is chosen, and space and layout for keeping both in one room is covered in a separate guide.

Frequently asked questions

Will cardio stop me building muscle?

The 2022 meta-analysis found no significant difference in hypertrophy between concurrent training and strength training alone.

Should I lift before cardio?

One meta-analysis found slightly higher lower-body one-repetition maximum when strength came first, with no effect on aerobic capacity. The difference was modest.

Is HIIT on a bike worse for leg strength than running?

One analysis showed a non-significant trend in that direction. Another found no significant difference by aerobic type, so the evidence does not settle it.

The bottom line

Meta-analyses find that adding aerobic training to strength training does not significantly reduce muscle size or maximal strength in healthy adults, though explosive strength and, in one analysis of interval training, lower-body strength may gain less. Same-session training and strength-second ordering are associated with somewhat larger penalties. Equipment for both can therefore coexist in a home gym, and the main decision is scheduling rather than choosing one over the other.

Sources

• Schumann M et al., “Compatibility of Concurrent Aerobic and Strength Training for Skeletal Muscle Size and Function: An Updated Systematic Review and Meta-Analysis”, Sports Medicine, 2022
• “The physiological effects of concurrent strength and endurance training sequence: A systematic review and meta-analysis”, 2018
• “The compatibility of concurrent high intensity interval training and resistance training for muscular strength and hypertrophy: a systematic review and meta-analysis”, 2018

Heart-rate zones on cardio equipment and in apps usually rest on an estimate of maximum heart rate, and the most familiar estimate is 220 minus age. Research has tested this and several alternative equations against measured maximum heart rate. This article summarises four studies, the equations they support and the size of the error they report. It concerns general exercise physiology in healthy people and is not medical advice; anyone with a heart or health condition should follow their clinician’s guidance on exercise intensity.

The equations in circulation

The equations named in the studies below include:

• 220 minus age, the most commonly used;
• 208 minus 0.7 times age, from a 2001 meta-analysis by Tanaka and colleagues;
• 211 minus 0.64 times age, from the Norwegian HUNT Fitness Study of 2013;
• 209.3 minus 0.72 times age, from a US registry analysis of 4,796 people.

Worked through for a 40-year-old, 220 minus age gives 180 beats per minute, the Tanaka equation gives 180, the HUNT equation gives about 185 and the registry equation about 181. For a 55-year-old the same equations give 165, about 170, about 176 and about 170. The equations differ most at older ages, which is where the studies report the largest disagreement.

The 2001 meta-analysis

Tanaka, Monahan and Seals gathered group mean values from 351 studies covering 492 groups and 18,712 subjects. Maximum heart rate was strongly related to age (r = -0.90), and the regression equation was 208 minus 0.7 times age. A laboratory study of 514 healthy subjects gave a virtually identical equation, and the line did not differ between men and women or with habitual physical activity. The authors concluded that the then-current 220 minus age formula underestimates maximum heart rate in older adults.

The HUNT Fitness Study

Nes and colleagues measured maximum heart rate in 3,320 healthy men and women where a maximal effort was verified. Age alone explained the result with the formula 211 minus 0.64 times age, and there was no evidence of interaction with gender, physical activity, fitness level or body mass index. They found that the earlier equations underestimated measured maximum heart rate in subjects older than 30. Importantly, they report a standard error of the estimate of 10.8 beats per minute and say it must be taken into account, meaning even the better equation leaves a wide range around any individual.

The registry analysis

A study using the FRIEND Registry analysed 4,796 apparently healthy people who reached maximal effort on a treadmill test. The fitted equation was 209.3 minus 0.72 times age, with a correlation of 0.61 and a standard error of estimate of 11.35 beats per minute. The mean difference between measured and predicted maximum heart rate was not significantly different from zero, but the limits of agreement were about plus or minus 25 beats per minute and there was a significant proportional bias. The authors advise against using age-predicted maximum heart rate as a measure of whether a person has made a maximal effort.

Comparing nine equations in a general sample

Shookster and colleagues (2020) compared nine equations, including those named by Fox, Tanaka, Nes and Gellish, against 99 graded treadmill exercise tests that ended at volitional fatigue with a respiratory exchange ratio above 1.10. Significant differences from measured values were found for the Gulati, Astrand, Nes and Fairbarn (male) equations, and Bland-Altman plots showed wide limits of agreement for all nine, meaning poor agreement between predicted and measured maximum heart rate. Proportional bias meant equations tended to underestimate at lower measured values and overestimate at higher ones, with the exception of the Fox equation (220 minus age), which the authors suggest may be the best option for a general population because it is less likely to under- or overestimate. They advise individuals to use data from a graded exercise test to determine maximum heart rate when possible.

What the disagreement means in practice

The studies point in different directions on which equation is best, which is itself informative: none is reliable for an individual. A rough illustration: a person predicted at 180 beats per minute could, with an error of about 25 beats either way, have a true maximum anywhere from about 155 to 205. Seventy per cent of those two figures is around 109 and 144 beats per minute, so a zone set from the formula could feel very different in practice from what the label suggests. Any zone programme, whether on a machine, a watch or an app, that begins from an age-based estimate inherits this uncertainty.

Practical points when using zones

• Treat zones as approximate ranges, not targets to the beat.
• Use perceived effort alongside heart rate. A related guide on this site covers rating of perceived exertion for strength work, and the same principle of checking a number against how hard the effort feels applies to cardio.
• Where accuracy matters, a supervised maximal test is the route the studies point to, rather than another formula.
• Different tools may use different equations, so a change of device can change the zones without any change in fitness.

Frequently asked questions

Is 220 minus age wrong?

It is approximate. The 2001 meta-analysis and the HUNT study found it underestimates in older adults, while a later sample of 99 tests found it less prone to bias than several alternatives. Every study reports wide individual error.

Which equation is most accurate?

The studies do not agree on one, and the standard errors reported (10.8 and 11.35 beats per minute) show a wide range around any prediction.

The bottom line

Age-based equations give a reasonable population average but a poor individual answer, with errors of roughly 10 to 11 beats per minute for one standard deviation and about 25 for the limits of agreement in the largest registry sample. Heart-rate zones set from them should be treated as a rough guide, checked against perceived effort and, where precision matters, against a supervised maximal test.

Sources

• Tanaka H, Monahan KD, Seals DR, “Age-predicted maximal heart rate revisited”, Journal of the American College of Cardiology, 2001
• Nes BM et al., “Age-predicted maximal heart rate in healthy subjects: The HUNT fitness study”, Scandinavian Journal of Medicine & Science in Sports, 2013
• “Revisiting age-predicted maximal heart rate: Can it be used as a valid measure of effort?” (FRIEND Registry), 2016
• Shookster D et al., “Accuracy of Commonly Used Age-Predicted Maximal Heart Rate Equations”, International Journal of Exercise Science, 2020

A common question for anyone buying a treadmill is whether running or walking on one is comparable to doing so outdoors. Systematic reviews of crossover studies, where the same people do both, give a more careful answer than either “identical” or “completely different”. This article summarises three of them, on running biomechanics, running physiology and performance, and walking. All involved healthy adults, and none evaluates individual treadmill brands.

Running biomechanics

Van Hooren and colleagues (2020) pooled 33 crossover studies with 494 participants comparing lower-limb biomechanics on a motorised treadmill and overground. They included only non-inclined, non-cushioned treadmill running at quasi-constant speed. The main conclusion was that spatiotemporal, kinematic, kinetic, muscle-activity and muscle-tendon outcomes were largely comparable, and most outcomes did not differ between conditions. The differences that did appear were:

• a smaller sagittal foot-ground angle at footstrike on the treadmill (mean difference 9.8 degrees, low-certainty evidence);
• differences in knee flexion at footstrike and knee flexion range of motion during stance, both graded low certainty;
• less vertical displacement of the centre of mass or pelvis (1.5 cm, low certainty);
• a slightly longer contact time (5 ms, low certainty);
• a lower peak propulsive force (0.04 body weights, very low certainty) and a difference in ankle joint moment, each based on pooled results from only two studies.

The authors advise care when extrapolating treadmill running biomechanics to overground running, particularly at footstrike. Their limitations note that most studies compared treadmill running with a laboratory runway rather than concrete or road surfaces, so real-world differences may be larger than reported. Conflicting results were found for the amplitude of muscle activity.

Running physiology and performance

A 2019 Sports Medicine systematic review of 34 crossover studies compared physiological, perceptual and performance measures. Twelve studies set the treadmill at a 1% grade and three used steeper grades. Key findings:

• oxygen uptake at submaximal speeds was similar on the treadmill at 0% and 1% grade to overground, while blood lactate was lower on the treadmill;
• heart rate and rating of perceived exertion on the treadmill were higher at faster submaximal speeds and lower at slower submaximal speeds than overground;
• at maximal running intensity, oxygen uptake and heart rate were similar between treadmill and overground;
• endurance performance was poorer on a motorised treadmill (standardised mean difference -0.50, with a confidence range shown as 0.36), while sprint performance varied considerably and was not significantly different.

The review’s conclusion is deliberately measured: some, but not all, variables differ between treadmill and overground running, and may depend on the speed at which they are assessed. That is a finding about pace-dependence and should not be read as saying a treadmill is better or worse.

Walking

A 2023 systematic review and meta-analysis of 55 studies with 1,005 healthy participants compared walking on a motorised treadmill and overground at matched speeds. It found that relative oxygen consumption (standardised mean difference 0.38) and cadence (0.22) were higher on the treadmill, while stride length (-0.36) and step length (-0.52) were lower. It reports that most kinetic variables differed between surfaces. The authors suggest the changes may reflect an attempt to increase stability given the lack of control, discomfort and unfamiliarity on the treadmill, and that treadmill construction, including surface stiffness and motor power, needs investigation.

A separate 2022 review of 22 studies with 409 young adults reached a similar overall verdict for walking: spatiotemporal, kinematic, kinetic, electromyographic and energy consumption measures were largely comparable, with some differences in kinematic, kinetic and electromyographic parameters.

What buyers can and cannot take from this

• Largely comparable does not mean identical. Small footstrike and stride differences appear, so gradual adaptation is reasonable, but the reviews give no personalised advice.
• Treadmill specifications are barely tested. The running biomechanics review excluded cushioned and inclined conditions, and the walking review says surface stiffness and motor power need investigation. Claims that a particular deck or motor makes running more natural are therefore unsupported by these reviews.
• Effort readouts may differ. Heart rate and perceived exertion depended on speed, so numbers seen on the treadmill may not map to outdoor effort at every pace.
• Endurance performance. Times on a treadmill may not match outdoor times, according to the 2019 review.

Readers comparing machines can pair this with the guides on this site covering motor ratings, deck cushioning and incline systems, which deal with specifications rather than physiology.

Frequently asked questions

Is running on a treadmill easier than running outside?

The reviews do not say so in general. Heart rate and perceived exertion were higher at faster speeds and lower at slower speeds on the treadmill, and endurance performance was poorer.

Does a 1% incline make it equivalent?

The physiology review reports similar oxygen uptake at both 0% and 1% grade, with lower lactate on the treadmill in each case. It does not present 1% as a proven correction.

Do the findings apply to everyone?

The reviews covered healthy adults aged 18 to 65 or, for one review, 20 to 40, so no conclusions follow for other groups.

The bottom line

Systematic reviews find treadmill and overground running and walking largely comparable, with specific differences in footstrike mechanics, stride length, effort at different speeds and endurance performance. The evidence is mostly low certainty and from healthy adults, and it does not test individual treadmill designs. Buyers should treat the treadmill as a good but not identical stand-in for outdoor exercise.

Sources

• Van Hooren B et al., “Is Motorized Treadmill Running Biomechanically Comparable to Overground Running? A Systematic Review and Meta-Analysis of Cross-Over Studies”, Sports Medicine, 2020
• “A Systematic Review and Meta-Analysis of Crossover Studies Comparing Physiological, Perceptual and Performance Measures Between Treadmill and Overground Running”, Sports Medicine, 2019
• “Physiological, perceptual, and biomechanical differences between treadmill and overground walking in healthy adults: A systematic review and meta-analysis”, 2023
• “Is treadmill walking biomechanically comparable to overground walking? A systematic review”, 2022

Eccentric training, where the muscle lengthens under load while a weight is lowered, is often marketed as a reason to buy specific equipment, particularly flywheel trainers that promise eccentric overload. Several meta-analyses have examined the underlying claims. This article summarises what they found, at the strength the evidence supports, and turns the results into questions a buyer can ask. It reports general research and is not advice for people with injuries or medical conditions.

Eccentric against concentric training in healthy adults

Roig and colleagues (2009) reviewed 20 randomised controlled trials comparing eccentric with concentric resistance training in healthy adults. Their findings were:

• when eccentric exercise was performed at higher intensities than concentric training, total strength and eccentric strength increased significantly more;
• strength gains after eccentric training appeared more specific, in terms of velocity and mode of contraction, than gains after concentric training;
• eccentric training at high intensities was more effective in promoting increases in muscle mass measured as muscle girth, with a trend towards greater muscle cross-sectional area on imaging;
• the authors relate the advantage to the higher loads developed during eccentric contractions, and note that further research is needed on how far the gains transfer to more complex movements.

The caution is in the wording: the superiority appeared when eccentric work was done at higher intensity, and the gains were specific. It is a finding about load and specificity, not a claim that any eccentric emphasis beats normal lifting.

Flywheel training and eccentric overload

Flywheel devices use the inertia of a spinning wheel instead of a weight stack. Maroto-Izquierdo and colleagues (2017) pooled nine randomised trials, with 276 subjects and 92 effect sizes, of flywheel training with eccentric overload in athletes and healthy subjects. The pooled effect estimate was 0.63 (95% confidence interval 0.49 to 0.76). The authors conclude that the analysis supports flywheel eccentric-overload training as superior to traditional weight-stack exercise for strength, power and size in healthy subjects and athletes.

Two boundaries apply. The comparison in that review is against traditional weight-stack exercise, not against free weights or against every form of eccentric-emphasis training. And nine trials is a small evidence base, so the finding is best read as supportive rather than settled.

Does a flywheel device actually deliver eccentric overload?

A 2021 systematic review and meta-analysis looked at how flywheel training is monitored in real time (28 articles in the review, 17 in the meta-analysis). It reports that an eccentric overload was not always achieved using flywheel devices. It also found that a cylindrical shaft, as against a conical pulley, and a low moment of inertia showed higher possibilities of achieving eccentric overload, and it advises a cylindrical shaft type with low moments of inertia where overload is the aim. For a buyer, that changes the question from “is it a flywheel?” to “does this configuration produce overload for the way it will be used?”, which the manufacturer’s marketing may not answer.

Older adults

A 2022 systematic review with meta-analysis compared eccentric with traditional or concentric exercise in adults over 55, pooling 19 papers. Results were mixed:

• for isometric knee strength the pooled effect favoured eccentric exercise (standardised mean difference 0.50) but was not statistically significant (P = 0.160);
• eccentric exercise gave greater improvements in the timed up and go test (SMD -0.68), the 2-minute sit-stand test (0.53) and the 30-second sit-stand test (0.81), but not the 6-minute walking test (0.01);
• the effects on body composition and muscle architecture were described as unclear.

The authors conclude that eccentric exercise is superior to, or at least as good as, concentric exercise for function in older adults. That is a statement about older adults as a group and should not be extended to other populations or to specific machines.

Reading the marketing claims

• “Eccentric overload”: ask what evidence shows the device achieves it in the reviewed configuration, since the monitoring review found it was not always reached.
• “Superior to weights”: the flywheel meta-analysis compared with weight-stack exercise, so a claim against barbells or dumbbells is not supported by it.
• “Faster results”: the eccentric review found greater gains at higher intensities and with high specificity, not a general speed advantage.
• Extending across categories: results for flywheel devices do not automatically apply to cable machines, resistance bands or slow-lowering technique with ordinary weights.

Practical points for a home setup

The 2009 review credits the higher loads developed during eccentric contractions for the advantage it found. Higher eccentric loads are a reason to review rack safety arrangements such as pins, safety arms and straps, which are covered elsewhere on this site.

Frequently asked questions

Is eccentric training better than normal lifting?

The 2009 meta-analysis found larger strength and girth gains when eccentric work was done at higher intensities than concentric work, with gains that were more specific. It did not show that it is better in every situation.

Do flywheel machines beat free weights?

No head-to-head comparison is reported in the meta-analysis summarised here. Its comparator was traditional weight-stack exercise.

What did the older-adult review find?

Greater improvements on several functional tests and no significant advantage on others, with unclear effects on body composition.

The bottom line

Meta-analyses support eccentric emphasis at higher intensities and flywheel eccentric-overload training against weight-stack exercise, but the evidence bases are modest and the comparators specific. A separate review shows overload is not guaranteed on every flywheel setup. Buyers should treat claims of superiority over other equipment as unproven and check the design details that affect overload before paying a premium.

Sources

• Roig M et al., “The effects of eccentric versus concentric resistance training on muscle strength and mass in healthy adults: a systematic review with meta-analysis”, British Journal of Sports Medicine, 2009
• Maroto-Izquierdo S et al., “Skeletal muscle functional and structural adaptations after eccentric overload flywheel resistance training: a systematic review and meta-analysis”, Journal of Science and Medicine in Sport, 2017
• “The use of real-time monitoring during flywheel resistance training programmes: how can we measure eccentric overload? A systematic review and meta-analysis”, 2021
• “The Effect of Eccentric vs. Traditional Resistance Exercise on Muscle Strength, Body Composition, and Functional Performance in Older Adults: A Systematic Review With Meta-Analysis”, 2022

Training volume, usually counted as the number of hard sets performed, is the variable most often discussed when a home training plan stops working. Three published meta-analyses have pooled trial data on how the number of sets relates to gains in muscle size and strength. This article summarises what each reports, how they count volume differently, and where their limits lie. It covers general evidence about resistance training and is not advice for anyone with an injury or health condition.

Why the counting method matters

The reviews do not use the same unit. Schoenfeld and colleagues (2017) count weekly sets per muscle group. Ralston and colleagues (2017) count weekly sets per exercise, and Krieger (2010) compares single with multiple sets per exercise. A figure such as “10 sets” therefore means different things depending on the paper, and numbers cannot be lifted from one review and applied to another.

Muscle size: the 2017 dose-response meta-regression

Schoenfeld, Ogborn and Krieger pooled 34 treatment groups from 15 studies and related weekly sets to changes in muscle size. Their main results were:

• with weekly sets treated as a continuous variable, volume had a significant effect on muscle size (P = 0.002), and each additional set was associated with a larger effect size of 0.023, which the authors equate to a 0.37% larger percentage gain;
• when studies were split into lower and higher volume conditions, the difference in effect size was 0.241, equivalent to a 3.9% difference in percentage gain (P = 0.03);
• when weekly sets were grouped as fewer than 5, 5 to 9 and 10 or more per muscle, the result was only a trend (P = 0.074).

The authors conclude that the findings indicate a graded dose-response relationship, with greater hypertrophy at higher volumes. The categorical result is worth noting, since it did not reach the usual significance threshold, and these are associations across studies rather than a controlled comparison of one person at different volumes.

Single sets against multiple sets

Krieger’s earlier meta-analysis analysed 8 studies (19 treatment groups) on muscle hypertrophy. Multiple sets per exercise were associated with a larger effect size than a single set, with a difference of 0.10. In a dose-response model, 2 to 3 sets and 4 to 6 sets each showed a trend towards a larger effect than 1 set, but there was no significant difference between 2 to 3 sets and 4 to 6 sets (P = 0.29). The paper’s summary is that multiple sets were associated with 40% greater hypertrophy-related effect sizes than one set, in both trained and untrained subjects. Taken together, the 2010 and 2017 hypertrophy analyses both associate more sets with more growth, and neither identifies a clear point beyond which extra sets stop helping.

Strength: the 2017 weekly-set meta-analysis

Ralston, Kilgore, Wyatt and Baker examined strength rather than size. They pooled 61 treatment groups from nine studies and classed weekly sets per exercise as low (5 or fewer), medium (5 to 9) or high (10 or more). Their findings were:

• strength gains were greater with high weekly sets than with low, with a mean effect size difference of 0.18 (95% confidence interval 0.06 to 0.30), the mean effect sizes being 0.82 for low and 1.01 for high;
• medium sets produced marginally greater gains than low (difference 0.15, confidence interval 0.01 to 0.30, P = 0.04), with heterogeneity between the seven studies in that comparison of 74%;
• the authors describe a graded dose-response relationship between weekly sets and strength gain, and suggest that for novice and intermediate male trainees low set numbers did not lead to the strength gains seen with medium or high volumes.

The paper lists its own limitations. The number of suitable studies was small, only one of the nine used a randomised control design, and the analysis was restricted to male populations. The authors also note that some of the strength increases may reflect repeated one-repetition-maximum testing, a learning effect, rather than the extra sets themselves.

What the evidence supports, and what it does not

• Supported: on average, trials with more weekly sets show larger gains in both muscle size and strength than trials with very few sets.
• Uncertain: how the response differs between individuals, how volume interacts with load, frequency or recovery, and whether results in the studies’ participants transfer to any given home trainee.
• Not established by these papers: an exact optimum. The reviews describe a graded relationship on average.
• Sex: the strength meta-analysis included men only, so it cannot be applied directly to women.

Where equipment enters

These reviews say nothing about products. Equipment matters only in that it determines whether a planned number of sets can actually be performed, for example through enough load range on adjustable dumbbells or a bench and rack that allow the exercises to be trained safely. A related guide on this site covers progressive overload when weights cannot simply be added.

Frequently asked questions

Is one set enough?

Krieger’s meta-analysis found multiple sets were associated with a larger hypertrophy effect than one set, and Ralston’s found low weekly sets produced the smallest strength gains. Neither is a statement about any individual.

Do more sets always give more muscle?

The 2017 meta-regression describes a graded relationship on average. The reviews do not identify a ceiling, and the categorical comparison in that paper was not significant.

Why do the reviews give different set numbers?

They count differently: the 2017 size review counts sets per muscle group per week, while the strength review counts sets per exercise per week.

The bottom line

Meta-analyses of resistance training trials consistently associate more weekly sets with larger gains in muscle size and strength than one set or very few, with the clearest contrasts between very low volumes and higher ones. They count volume differently, contain small numbers of studies and cannot fix an ideal figure, so a plan should be treated as a starting point to adjust and not a formula to copy.

Sources

• Schoenfeld BJ, Ogborn D, Krieger JW, “Dose-response relationship between weekly resistance training volume and increases in muscle mass: A systematic review and meta-analysis”, Journal of Sports Sciences, 2017
• Krieger JW, “Single vs. multiple sets of resistance exercise for muscle hypertrophy: a meta-analysis”, Journal of Strength and Conditioning Research, 2010
• Ralston GW, Kilgore L, Wyatt FB, Baker JS, “The Effect of Weekly Set Volume on Strength Gain: A Meta-Analysis”, Sports Medicine, 2017