Single-leg training is not the sprint shortcut it is sold as

Sprinting, jumping forward and changing direction all happen with force applied largely through one leg at a time. That observation underpins a popular coaching argument: if the movement is unilateral, the training should be too, so split squats and single-leg work should transfer to speed better than barbell squats. It is a tidy theory built on the principle of training specificity, but theory is not evidence. This review set out to test the claim directly, comparing bilateral and unilateral resistance training for their effects on horizontally orientated movement performance such as sprinting.

The authors searched Google Scholar, CrossRef and PubMed for studies in healthy participants that included a resistance training intervention comparing bilateral and unilateral exercise on a measure of movement speed, such as sprinting. Eligible studies were pooled using an inverse-variance random-effects meta-analysis. Effects were expressed as standardised mean differences with 95% confidence ranges, and the analysis also broke results down by training type: strength work alone, plyometric work alone, and combined strength plus plyometric programmes.

Both modalities worked. Bilateral training produced a moderate effect on horizontal movement performance (0.60) and unilateral training a very similar one (0.57), and the direct comparison between the two showed no meaningful difference (0.17, not statistically significant). The breakdown by training type was arguably more interesting: for bilateral work, combined strength and plyometric training had the largest effect (0.88), ahead of plyometrics alone (0.55) and strength alone (0.42). For unilateral work, plyometrics led (0.78), followed by combined training (0.63), with strength alone clearly weakest (0.29).

The result runs contrary to popular opinion, as the authors themselves put it, and complicates a simple reading of training specificity: matching the limb pattern of the target movement did not produce better transfer. It does not say unilateral training is useless; it was clearly effective, and there may be other reasons to programme it. What the analysis cannot settle is whether particular athletes, sports or experience levels respond differently, since the pooled trials varied considerably. The stronger signal may be about exercise type, with plyometric and combined programmes consistently outperforming pure strength work for speed.

If you have been told single-leg exercises are essential for getting faster because sprinting is a one-legged act, this is a reason to relax about it: both approaches improved speed in these pooled trials, and neither beat the other. The more useful signal is that explosive, plyometric-style work, especially alongside strength training, showed the largest effects on horizontal performance. This is information about averages across trials, not a programme, and an athlete's individual needs, sport and injury history still shape sensible exercise selection.