Whether a leg press should be done two legs at a time or one leg at a time is a genuinely debated question in strength training, not a settled one. Two recent systematic reviews and meta-analyses, one focused on muscle growth and strength, one on athletic performance measures, give a consistent answer: the choice matters less for muscle size than many equipment marketers imply, and more for exactly which kind of strength or power you are training.
What the evidence shows on muscle growth
A 2025 systematic review and meta-analysis in Sports Medicine, led by Witalo Kassiano and colleagues, searched three databases and, after screening 703 studies, included 9 that directly compared unilateral (one limb at a time) against bilateral (both limbs together) resistance training. The result on hypertrophy was clear: “we found no evidence of differential muscle hypertrophy between the two exercise selections” (effect size: -0.21, 95% CI: -3.56 to 3.13, P = 0.57), a confidence interval wide enough, and centred close enough to zero, to rule out a meaningful difference either way rather than merely failing to detect one. The review rated the overall risk of bias across included studies as moderate.
Strength gains follow the principle of specificity
Where the same review did find a clear difference was in strength testing, and the pattern was exactly what training specificity would predict. Bilateral training produced a significantly larger increase in bilateral strength (effect size: 0.56, 95% CI: 0.16 to 0.96, P = 0.01), while unilateral training produced a significantly larger increase in unilateral strength (effect size: -0.65, 95% CI: -0.93 to -0.37, P = 0.001). The authors’ conclusion is direct: “strength gains appear to follow the principle of specificity,” meaning the way you test strength, on one limb or two, tends to favour whichever way you trained it, independent of any underlying difference in muscle growth.
Performance measures: jump, sprint and change of direction
A separate systematic review and meta-analysis of 14 studies (392 participants, aged 16 to 26) looked specifically at athletic performance outcomes rather than hypertrophy or basic strength testing. It found unilateral training produced a large effect on unilateral jump performance (effect size: 0.89) and bilateral training produced a small effect advantage on bilateral strength (effect size: -0.43), broadly consistent with the specificity pattern in the Sports Medicine review. It found no significant differences between unilateral and bilateral training for unilateral strength, bilateral jump performance, change-of-direction speed, or linear sprint speed, outcomes where the training method used did not clearly determine the result either way.
This second review carries real limitations worth stating plainly: every included study used lower-body exercises, so the authors note “whether the present findings…can be applied to the upper limbs remains unclear,” the participant age range was restricted to 16 to 26, and the authors rated overall study quality as moderate. Because several subgroups contained fewer than 10 studies, the authors could not run a meta-regression to investigate why individual results varied.
What this means for choosing equipment and exercises
Neither review supports the idea that switching a training programme heavily toward unilateral work, single-leg presses, single-arm rows, split squats, will produce more muscle growth than bilateral equivalents at matched effort and volume. What the evidence does support is choosing the training pattern that matches your actual goal: bilateral movements for bilateral strength (most standard lifts, and most gym machines), unilateral movements specifically where unilateral strength or unilateral jump performance is the target, relevant to sports involving single-leg take-offs or change of direction, or to correcting a known side-to-side imbalance.
For home equipment specifically, this also has a practical footprint implication: a single adjustable bench and a pair of dumbbells can deliver both unilateral and bilateral versions of most exercises without needing separate specialised machines for each, since the difference between the two approaches is how an exercise is performed rather than which piece of equipment is strictly required to perform it.
Frequently asked questions
Does unilateral training build more muscle because of extra stabiliser demand? The Sports Medicine meta-analysis found no significant hypertrophy difference between unilateral and bilateral training, so this common claim is not supported by the pooled evidence, though the number of included studies (9) remains limited.
Should athletes in sports with single-leg actions train unilaterally? The performance-focused review found unilateral training produced a large effect specifically on unilateral jump performance, which is relevant to single-leg-dominant sports, though the evidence is drawn from a young (16 to 26), lower-body-only sample.
Is bilateral training better for general strength training at home? Bilateral training showed a clear advantage for bilateral strength specifically, which is what most home strength goals and standard equipment (barbells, most machines) are built around, but this does not make unilateral work unnecessary if single-limb strength or balance is also a goal.
The bottom line
Across two systematic reviews and meta-analyses, unilateral and bilateral resistance training produced no detectable difference in muscle growth, while strength and jump gains followed the principle of specificity: training bilaterally builds bilateral strength, training unilaterally builds unilateral strength and unilateral jump ability. The practical choice is a matching exercise, not a superior one.
Sources
- Kassiano W, et al., “Comparison of Muscle Growth and Dynamic Strength Adaptations Induced by Unilateral and Bilateral Resistance Training: A Systematic Review and Meta-Analysis,” Sports Medicine, 2025 (PubMed)
- “Effects of Unilateral vs. Bilateral Resistance Training Interventions on Measures of Strength, Jump, Linear and Change of Direction Speed: A Systematic Review and Meta-Analysis,” PMC