Nonlinear analysis reveals duration and gradient-dependent disruption of load carriage gait variability during an outdoor 6.72 km time trial in military personnel

This investigation assessed the effect of gradient and duration on the gait variability exponent, DFA-α, in military personnel affixed with dual inertial measurement units performing a load carriage time-trial. Gait data (N = 14) were partitioned into 256 stride time segments by gradient (uphill, downhill) using a gait event algorithm. Detrended fluctuation analysis calculated DFA-α per segment, which was averaged across one-third durations (phases 1–3) per gradient. Two-way repeated measures ANOVA examined effects of gradient, duration, and interaction on DFA-α, with Bonferroni-adjusted post-hoc comparisons. There was a significant main effect of duration (phase 1: 0.593 ± 0.021; phase 2: 0.563 ± 0.031; phase 3: 0.493 ± 0.021; F = 3.833, p = 0.035, η_p² = 0.228), but not gradient (uphill: 0.486 ± 0.031; downhill: 0.614 ± 0.035; F = 4.252, p = 0.060, η_p² = 0.246), or interaction (F = 0.019, p = 0.981, η_p² = 0.001). Pairwise comparisons revealed significantly lower DFA-α during phase 3 than phase 1 (p = 0.016). Elapsed duration and uphill gradient, despite a large, but non-significant effect, may represent factors altering gait variability for injury risk.