The review, led by Antonio Martos-Arregui of the University of Granada together with colleagues in Spain and Chile, followed the PRISMA 2020 reporting guidelines and was prospectively registered with PROSPERO before the data were examined. The team searched Web of Science, PubMed, and SPORTDiscus up to April 2025, casting a deliberately broad net across training interventions that targeted the lower limbs. After screening 708 records, winnowing them through title, abstract, and full-text review, and recovering two additional studies from reference lists and related-article searches, eleven studies involving a total of 297 athletes made the final cut. Crucially, the review was not simply asking whether training works. It was asking whether training that is explicitly individualized around an athlete’s measured asymmetries outperforms generic programs, and whether unilateral training beats bilateral training even when nobody bothers to tailor it.

The distinction matters more than it might first appear. Most previous syntheses had lumped all interventions together or focused narrowly on a single training modality. An earlier meta-analysis by Bettariga and colleagues found small to moderate effects of both unilateral and bilateral strength training on reducing asymmetries in tests such as the single-leg countermovement jump, but it never separated programs designed specifically to shrink the gap from those that happened to shrink it as a side effect. A more recent meta-analysis by Sun and colleagues concluded that unilateral plyometric training reliably reduces lower-limb asymmetries where bilateral and complex training do not, yet it confined itself to plyometrics and ignored eccentric overload work, conventional strength training, and combined approaches. The Granada-led review was designed to fill exactly that gap, comparing like with like and asking the sharpest possible version of the question.

The eleven studies fell into two broad families. The first, comprising seven studies, applied different training stimuli to each limb, usually after a pre-test identified the weaker side through performance-based measures rather than self-reported preference. Some protocols simply started every unilateral set with the weaker leg while keeping volume equal. Others went further, doubling or even tripling the training volume assigned to the weaker limb. Training modalities ranged from plyometrics and weight lifting to lateral squats performed on conical pulley devices and vibration platforms, applied to soccer players, basketball players, and athletes from other sports between 2017 and 2025. The second family, four studies, pitted standard unilateral training against bilateral training without tailoring anything to baseline asymmetries, allowing the reviewers to ask whether simply going single-legged was enough.

On the first question, the answer leaned clearly toward the individualized approach. Across the studies that manipulated exercise order, beginning each set with the weaker leg produced more consistent reductions in asymmetry measures, from single-leg horizontal jump asymmetry to concentric peak power imbalances in lateral squat testing, than beginning with the stronger leg. In one soccer study, the weaker-leg-first group outperformed a bilateral training group on countermovement jump height, a 180-degree change of direction task, and unilateral squat peak power on both sides. The pattern extended to performance outcomes, with several studies showing that groups prioritizing the weak limb gained more across jump tests and power measures than groups that trained the strong limb first. One study, notably, found no meaningful between-group differences, a reminder that sequencing alone is not a guarantee.

Adding volume sharpened the effect. In two studies from the same research group, participants who started sets with the weaker leg and applied double training volume showed greater reductions in asymmetry indices and larger performance gains than those who merely started with the weak leg or, tellingly, than those who started with the strong leg. Two further recent studies tested an even more aggressive prescription, tripling the volume on the weaker side, and reported encouraging results, including greater reductions in change-of-direction deficit asymmetry and improvements in jump height, bilateral horizontal jump distance, and one-repetition maximum squat strength compared with control conditions. The mechanistic logic, as the review authors frame it, is that the weaker limb represents a window for development: trained fresh, before fatigue accumulates, and with a heavier overload, it receives a superior neuromuscular stimulus that may gradually close the gap with its counterpart.

The mirror-image finding is just as striking. Starting unilateral exercises with the stronger leg, a sequence that might feel natural because the strong side dominates first, showed no consistent benefit for reducing asymmetries and generally produced smaller performance improvements than the weaker-first alternatives. The explanation offered is subtle but compelling: when the weaker limb is always trained second, it works under accumulated fatigue, compromising the quality of its neuromuscular recruitment and potentially widening the very gap the training is meant to close. What looks like a trivial detail of gym logistics, which leg goes first, may therefore quietly reinforce the imbalance that sport-specific practice has already built.

The comparison between untailored unilateral and bilateral training produced a messier picture. Of the four relevant studies, only one, in youth male basketball players, found that unilateral training clearly outperformed control groups in reducing asymmetries across isometric strength and functional tests, while the other three reported no significant between-group differences in asymmetry outcomes. Performance results followed a task-specific pattern that echoes a well-established principle in exercise science: unilateral training tended to produce greater gains on single-limb tests, while bilateral training excelled on bilateral tasks. In one soccer study, the bilateral group beat the unilateral group on a range of two-legged tasks even as the unilateral group dominated single-limb measures. The review authors suggest this specificity arises because sprinting, jumping, and changing direction are inherently unilateral actions, and because single-leg work prevents the stronger limb from compensating for the weaker one during lifts, but they are careful to note that the underlying mechanisms remain largely speculative.

Honesty about limitations is where this review distinguishes itself. Only eleven studies qualified, sample sizes ranged from 18 to 66 participants, two of the included publications drew on the same cohort and were counted once, and the risk-of-bias assessment using a modified Cochrane tool revealed uneven methodological quality, with only four studies rated low risk for random sequence generation and four showing participant dropout exceeding twenty percent. More fundamentally, the field lacks standards. Limb dominance was defined inconsistently, sometimes by performance, sometimes by kicking preference, and no included study verified that baseline asymmetries exceeded the coefficient of variation of the assessment tool, meaning some of the asymmetries being trained might have been measurement noise rather than real biological differences. The direction and magnitude of asymmetry also fluctuate depending on the task and metric used, undermining any universal threshold such as the commonly cited ten to fifteen percent cutoff.

For coaches, the practical takeaway is refreshingly low-tech. Identifying the weaker limb with a simple performance test relevant to the task at hand, then starting unilateral exercises with that limb or assigning it extra volume, requires no additional equipment, no additional time, and carries no reported risk, yet appears more effective than generic programs for narrowing interlimb gaps and may add performance gains, particularly on single-limb tasks. The review’s authors recommend that dominance be judged by measured performance in the specific task being trained, not by questionnaires or habit, and that future studies verify baseline asymmetries against measurement error before intervening. Whether asymmetry-focused training ultimately delivers meaningful protection against injury, and whether the weaker limb’s closure of the gap translates into faster sprints and higher jumps on the field, remain open questions. But the direction of the evidence now points somewhere specific, and it points at the weaker leg first.

Subject of Research: The effectiveness of asymmetry-focused versus general training interventions in reducing interlimb asymmetries and improving athletic performance

Article Title: Are Asymmetry-Focused Training Interventions More Effective than General Programs in Reducing Interlimb Asymmetries and Improving Athletic Performance? A Systematic Review

Article References: Are Asymmetry-Focused Training Interventions More Effective than General Programs in Reducing Interlimb Asymmetries and Improving Athletic Performance? A Systematic Review. (n.d.). https://doi.org/10.1186/s40798-026-01119-5

Image Credits: AI Generated

DOI: 10.1186/s40798-026-01119-5

Keywords: interlimb asymmetry, sports medicine, systematic review, unilateral training, bilateral training, strength and conditioning, athletic performance, weaker limb, plyometric training, injury risk, training prescription, athletes