Does the different function of the lead vs. trail foot lead to functional asymmetry in balance performance of sub-elite youth cross-country mountain bikers? A pilot study

Background: During descents, cornering, or coasting over obstacles, cross-country mountain bikers use an isometric split stance with horizontally aligned pedals, establishing a distinct “lead” and “trail” leg. This pilot study investigated whether the different functions of the lead compared to the trail foot are associated with inter-limb functional asymmetry (FA) in proactive and reactive balance performance.

Methods: Twelve sub-elite youth cross-country mountain bikers (10 males, age: 13.5 ± 1.7 years, training history: 4.7 years) were assessed. Proactive balance was evaluated using the Y-Balance Test-Lower Quarter (YBT-LQ). Reactive balance was assessed via Time to Stabilization (TTS) during single-leg drop landings. Statistical analyses utilized Kruskal–Wallis H-tests and Wilcoxon signed-rank tests to compare performance differences between the lead and trail leg.

Results: No significant differences between the lead and trail leg were observed across any reach directions or the composite score of the YBT-LQ. Contrarily, TTS revealed a significant difference ( Z = 2.59, p = .010, r = .75) for the mediolateral plane, with the lead leg having a faster TTS.

Discussion: Chronic participation in mountain biking was associated with an FA in measures of reactive balance specifically isolated to the ML plane. Since off-road descents present unpredictable, high-speed perturbations, the rider must rely heavily on a mediolateral “hip strategy.” The superior reactive stabilization of the lead leg suggests that this specific FA could serve as a sport-specific performance indicator.