Author(s): CHEN, W., CHAN, W., GU, S., CHIU, W. , Institution: CHANG GUNG UNIVERSITY OF SCIENCE AND TECHNOLOGY, Country: TAIWAN, Abstract-ID: 2268

INTRODUCTION:
Walking is the most common form of physical activity among older adults, and daily living environments frequently present variations in slope. Compared with level walking, downhill walking requires greater eccentric muscle contraction and neuromuscular control, posing a functional challenge to aging individuals. Sarcopenia is characterized not only by declines in muscle mass and strength but also by the deterioration of neuromuscular control. Therefore, examining changes in muscle activation and timing under different slope conditions is essential for understanding the early functional manifestations of sarcopenia in older adults.This study aimed to investigate differences in lower-limb muscle activation levels, gait parameters, and muscle onset timing in healthy older adults walking at different downhill gradients (−5%, −7%, −9%) compared with level ground (0%). Furthermore, the study explored the association between these changes, age-related neuromuscular regulatory strategies, and the potential risk of sarcopenia.
METHODS:
Eight healthy older adults walked at their self-selected preferred speed on three downhill gradients and on level ground. Gait and muscle signals were collected synchronously using a motion capture system (Vicon T40, 100 Hz) and a surface electromyography system (BTS FreeEMG, 1000 Hz). Data were analyzed using Matlab 7.0.1. Cadence, step length, gait cycle duration, and the muscle activation levels and onset timing of the rectus femoris, biceps femoris, tibialis anterior, and gastrocnemius were compared across slope conditions using one-way ANOVA (p < .05).
RESULTS:
The findings indicated that: (1) increased slope inclination did not result in significant differences in cadence, step length, or gait cycle duration; (2) muscle activation levels of the rectus femoris, biceps femoris, tibialis anterior, and gastrocnemius did not significantly differ among slopes; (3) however, the activation sequence of major lower-limb muscles changed between downhill and level walking, with more pronounced timing adjustments observed beyond the −7% gradient.
CONCLUSION:
The results suggest that healthy older adults maintain stable gait parameters and muscle activation intensity during steeper downhill walking by modifying muscle activation timing. This phenomenon may reflect the initiation of neuromuscular compensatory mechanisms during aging and represent a functional regulatory strategy preceding the clinical onset of sarcopenia. Downhill walking tasks may serve as a potential functional assessment tool for evaluating neuromuscular control capacity and sarcopenia risk in older adults. Future studies should include individuals with sarcopenia to further verify neuromuscular regulation thresholds under varying slope conditions.