Effects of lead leg selection on bilateral landing force‐time characteristics: Return to sport testing implications

Abstract

We quantified the effect of lead leg selection on landing force–time characteristics during a vertical drop landing (VDL) initiated with a step‐off. Plyometric‐trained subjects (male: n = 8; female: n = 5; age =23 ± 3.3 years; body mass =74.4 ± 11.2 kg) performed 6 step‐off‐initiated VDLs from a 45‐cm box (n = 3/lead leg). Pooled and lead leg stratified between‐limb comparisons of limb‐specific initial ground contact timing, peak vertical ground reaction force (Fzpeak), and early landing‐phase impulse (Impulse100ms) were assessed by a two‐factor, within‐subject ANOVA, and limb symmetry indexes were calculated (α = 0.05). Pooled data showed that the lead leg made contact prior to the trail leg and contributed a greater fraction to Fzpeak compared with the trail leg. Stratifying trials by lead leg selection led to significant between‐limb differences in Fzpeak (p < 0.05) and Impulse100ms (p < 0.01) with the right leg leading but not with the left leg leading. Lead leg selection in step‐off‐initiated VDLs influenced landing performance and limb symmetry indexes of variables associated with lower limb injury risk, suggesting the need to control for lead leg selection in these tasks. A step‐off may not be a suitable technique to initiate landing tasks when assessing limb symmetry.

Why Sports Should Embrace Bilateral Asymmetry: A Narrative Review

“…Interestingly, pairwise comparisons showed that significant interlimb differences occurred only when the right leg led the movement, with the right leg making earlier ground contact and generating greater force and impulse than the left leg. Limb symmetry indices (LSI) generally showed asymmetries ≥10% [1]. This shows that even in a simple drop jump task (with low contextual interference), athletes exhibit marked interlimb asymmetry in their performance.…”

“…In addition, any findings from cross-sectional studies should be taken with a pinch of salt, since the relationships between interlimb asymmetry (magnitude and direction) and performance are not necessarily consistent across a sports season [34,39,42,63,64,67]. One study assessed the ground reaction forces (GRF) of 13 plyometrics-trained subjects (23 ± 3 years, 8 male and 5 female) after a 45-cm drop jump whereby the subjects had to change their lead leg (i.e., the leg initiating the movement to step off the box) [1]. Upon landing, the lead leg generated greater forces than the trail leg.…”

“…Regardless, we question if fixed, arbitrary interlimb symmetry thresholds should always be achieved, as was previously discussed. Unfortunately, several studies relate asymmetries to injury occurrence without even providing basic associative data [1][2][3][4][5][6][7][8][9][10], potentially due to a reliance on pre-conceived assumptions and beliefs on the subject. For example, in a previously mentioned study whereby athletes performed a drop jump task [1], the potential implications of the landing asymmetries towards injury occurrence were discussed at length.…”

“…Unfortunately, several studies relate asymmetries to injury occurrence without even providing basic associative data [1][2][3][4][5][6][7][8][9][10], potentially due to a reliance on pre-conceived assumptions and beliefs on the subject. For example, in a previously mentioned study whereby athletes performed a drop jump task [1], the potential implications of the landing asymmetries towards injury occurrence were discussed at length. However, this study did not directly assess injury occurrence, and so such asymmetries are merely the realization of a fact and should not be used to infer subsequent injury occurrence.…”

“…In sports training and fitness contexts, symmetry intuitively seems to be a concept that practitioners chase in the hope that it may enhance performance and/or reduce injury risk. Such is the strength of this belief that several studies associate lower limb bilateral asymmetries (e.g., ground reaction forces and kinematic analyses) with increased injury risk despite not actually having assessed any actual risk [1][2][3][4][5][6][7][8][9][10], i.e., the occurrence of injuries was not registered in such studies. Such unsubstantiated discourse misleads the readers and may even detract from analyzing other (relevant) variables of those works.…”