Effects of slope on lower-limb bilateral asymmetry and dynamic stability during running

To examine differences in lower-limb bilateral asymmetry and dynamic stability across running slopes at a fixed speed.

A repeated-measures secondary analysis of a publicly available multi-slope running biomechanics dataset was performed. Nineteen healthy runners ran at 2.78 m·s⁻¹ on five slopes from -6° to +6°. Asymmetry in five peak loading variables was determined using the percentage difference method. For the margin of stability (MoS) analysis, anteroposterior pelvic velocity was expressed relative to the treadmill belt by adding the belt speed of 2.78 m·s⁻¹; no belt-speed correction was required for the mediolateral calculation. Slope effects were analyzed using linear mixed-effects models with Benjamini-Hochberg control of the false discovery rate.

Significant slope effects were found for the asymmetry of Achilles tendon strain, knee extension moment, and patellofemoral stress and for both anteroposterior and mediolateral MoS (q < 0.05), but not for vertical ground reaction force or ankle plantarflexion moment asymmetry. Anteroposterior MoS increased monotonically, becoming less negative from -0.573 ± 0.021 m (-6°) to -0.523 ± 0.033 m (+6°; F₄, ₇₂ = 77.74, q < 0.001, partial η² = 0.81). Mediolateral MoS decreased from 0.062 ± 0.022 m (-6°) to 0.052 ± 0.031 m (+6°; F₄, ₇₂ = 3.50, q = 0.016, partial η² = 0.16). Achilles tendon strain asymmetry decreased from downhill to uphill running, whereas knee extension moment and patellofemoral stress asymmetry were greatest near mild uphill running.

Lower-limb bilateral load distribution and direction-specific mechanical margins varied across slopes. Load magnitude and bilateral asymmetry did not change in parallel, indicating that asymmetry may provide information complementary to absolute load. The strongly negative anteroposterior MoS values are mechanically plausible during running and should not, by themselves, be interpreted as evidence of global instability.