Negative Trend of Regularity of Locomotion in an Endurance Walking Task: Experimental Data from Healthy Adult Recreational Athletes in an Unsupervised 100 km March

(1) Background: Physical fatigue, either in short anaerobic exercises or in aerobic ones, affects locomotion patterns. Those effects, if consistently observed, may function as fatigue proxies. The present study focuses on the regularity of the pseudo-periodic acceleration patterns measured by a wearable sensor. Studies during laboratory anaerobic tasks on healthy subjects and on persons with multiple sclerosis during 6 min walking tests demonstrated that regularity decreases with fatigue. This study’s objective is to verify if the gait regularity during an unsupervised endurance aerobic walking task progressively decreases in healthy subjects. (2) Methods: Ten healthy male adults, not competitive recreational athletes, equipped with an accelerometer, participated in a non-competitive 100 km walk in about 24 h. (3) Results: Eight participants took from about 22 to 25 h to complete the task. Two did not finish. The trend of locomotion regularity (on average −6.3%, p < 0.001, effect size 1.41) was negative for all the participants. The gait speed decrease, in all the participants, explained less than 20% of the regularity decrease. Other outcome indices, such as that related to cadence, did not provide unique trends. (4) Conclusions: Regularity decrease is associated with fatigue in submaximal locomotor efforts; due to the experimental group limitations in size and composition, further studies should extend regularity assessments to women, and to persons with neuromuscular disabilities or attending walking rehabilitation.