Ground gradient affects stride-to-stride fluctuations and gait variability in overground walking

Purpose: This study aims to explore the impact of ground gradient on gait variability. Methods: Ten healthy adults (39.3 ± 4.14 years) performed overground walking under three gradient conditions: uphill 10.1° (17.81%), − 10.1° downhill (− 17.81%), and level 0.54° (0.95%). Gait kinematics were recorded using inertial measurement units, and stride time intervals were evaluated for variability magnitude and temporal structure via Coefficient of Variation (CV) and Detrended Fluctuation Analysis (DFA-α). Heart rate was recorded and served as a measure of exertion. Results: Significant differences in both CV and DFA-α emerged among conditions (p < 0.001). Downhill walking exhibited the highest CV (4.67 ± 1.65%) and the lowest DFA-α (0.62 ± 0.13). In contrast, uphill walking showed intermediate values (CV: 3.67 ± 0.84%; DFA-α: 0.76 ± 0.09), while level walking displayed the lowest CV (1.98 ± 0.62%) and the highest DFA-α (0.84 ± 0.1), demonstrating a parabolic effect of ground gradient with gait variability for both CV and DFA-α. Downhill walking also elicited faster average velocities (1.57 ± 0.14 m/s) compared to uphill (1.38 ± 0.09 m/s) and level (1.46 ± 0.08 m/s) walking. Conclusion: Interestingly, while uphill walking resulted in the highest heart rate (141.9 ± 13.8 bpm), DFA-α values of stride time intervals time series did not differ significantly from level walking, suggesting that metabolic effort may not be associated with the temporal structure of gait variability. Overall, it appears that during downhill walking, pronounced neuro-mechanical demands, likely imposed by eccentric effort, affect the amount and temporal structure of variability.