Effects Of Physical Fatigue On Lower Limb Inter-joint Coordination During Constant Speed Treadmill Walking

Movement coordination involves synchronized joint actions, crucial for tasks like walking. Central nervous system interactions and sensorimotor circuits are pivotal for achieving this. Physical fatigue can disrupt sensorimotor function, affecting walking. But understanding the specific impact of fatigue on inter-joint coordination during treadmill walking is limited. PURPOSE: To investigate potential alterations in inter-joint coordination resulting from physical fatigue induced by a high-intensity treadmill exercise. METHODS: Six healthy young adults (3 M/3F, 21.17 ± 2.23 yrs, 1.73 ± 0.09 m, 66.75 ± 8.45 kg) participated in this study. A progressive inclined treadmill walking protocol was applied, and respiratory exchange ratio (RER), heart rate (HR), and Borg rating of perceived exertion (RPE) were monitored to assess physical fatigue. Sagittal plane joint angles and velocities for the right leg during constant-speed treadmill walking pre and post-fatigue were calculated and interpolated to 100% of a gait cycle. Continuous relative phase (CRP) was employed to examine inter-joint coordination with the use of mean absolute relative phase (MARP), deviation phase (DP), and cross-correlation to indicate CRP variability. Paired t-tests examined the impact of fatigue on each variable. RESULTS: Average walking speed for all subjects was 1.54 m/s, and the RER, HR and RPE at the end of the fatigue protocol were 1.03, 178.7 bpm and 8.5, respectively. For the CRPhip-knee, post-fatigue MARP and DP during stance phase increased, but not significantly (127.2 ± 206.37 vs. 121.15 ± 54.69, p = .309; 29.41 ± 66.33 vs. 26.26 ± 22.50, p = .510), and there was no significant difference in MARP and DP before and after fatigue during swing phase (87.41 ± 55.65 vs. 86.54 ± 32.13, p = .675; 5.93 ± 4.15 vs. 6.02 ± 6.52, p = .941). For the CRPknee-ankle, post-fatigue DP during stance phase was higher (26.02 ± 32.26 vs. 22.95 ± 16.57, p = .400), and other parameters were no significant differences. Cross-correlation coefficients for both CRP patterns in pre and post-fatigue exceeded 0.832 in stance and 0.724 in swing phases. CONCLUSION: Physical fatigue may not change the inter-joint coordination of lower limb under treadmill walking, which may be due to constant-speed treadmill walking regulate inter-joint coordination.