Author(s): DHONDT, J., AERENHOUTS, D., BISHOP, C., DE PAUW, K., CLARYS, P., D'HONDT, E., CHAPELLE, L., Institution: VRIJE UNIVERSITEIT BRUSSEL, Country: BELGIUM, Abstract-ID: 773

INTRODUCTION:
Inter-limb asymmetry of the lower limbs has traditionally been viewed as detrimental to athletic performance, with thresholds of 10–15% commonly considered problematic. However, evidence supporting this assumption in male and female endurance runners of various training levels is limited, and the use of such arbitrary thresholds appears inconsistent with the task- and metric-specific nature of inter-limb asymmetries. Therefore, this study aimed to: (1) examine differences in isometric strength asymmetry by sex and training level, (2) compare running performance between high- and low-asymmetry groups using a task- and metric-specific approach, and (3) explore associations between lower inter-limb strength asymmetry and running performance.
METHODS:
Fifty-eight recreational endurance runners (34.2 ± 9.1 years, 50% male) completed six isometric strength tests assessing hip adduction and abduction, knee extension and flexion, ankle dorsiflexion and plantar flexion strength across one familiarisation and one testing session. Running performance was assessed using the Cooper test on an outdoor athletics track. Median-split analyses classified participants into high- and low-asymmetry groups per strength test. Between-group differences were evaluated using Kruskal–Wallis and Mann–Whitney U tests, and associations with running performance were examined using multiple linear regression.
RESULTS:
Asymmetry magnitudes ranged from 7.27% to 15.65%, with no significant differences according to sex or training level. Likewise, running performance did not differ significantly between asymmetry groups. Positive associations were found between running performance and asymmetries in knee flexion (p = 0.032, B = 10.276) and ankle plantar flexion (p = 0.004, B = 20.934), whereas other strength measures showed no significant associations.
CONCLUSION:
These findings indicate that lower inter-limb isometric strength asymmetries of up to ~16% are common among endurance runners and do not appear to impair running performance. Consequently, such a magnitude of asymmetry may reflect normal individual variation rather than a meaningful deficit.