Hip Flexor Muscle Activation Across Gait Phases in Healthy Young Adults: Effects of Step Length and Cadence Adjustments at a Constant Walking Speed.

Background Gait impairment is a critical issue in aging populations and is often characterized by a reduced step length and increased cadence. Although the iliopsoas (IL) and other hip flexors are essential for gait, the neuromuscular mechanisms underlying these compensatory changes remain unclear. Objective To investigate the phase-specific electromyographic (EMG) activity of the IL, sartorius (SA), rectus femoris (RF), and tensor fasciae latae (TFL) muscles during walking tasks that independently manipulate step length and cadence at a fixed walking speed. Methods In this exploratory study, nine healthy adult males performed the following three treadmill walking conditions at 5 km/h: (1) long step/low cadence, (2) normal gait, and (3) short step/high cadence. Surface EMG data from the four hip flexor muscles were collected and analyzed across the four gait phases. A motion-capturing system was used to assess kinematic parameters. EMG data were normalized to maximal voluntary isometric contraction (MVIC). Friedman tests with Benjamini-Hochberg false discovery rate (FDR) correction were used to compare muscle activity among the conditions. Results The IL activity increased significantly during the late swing phase in the long-step condition, whereas the SA and RF showed early activation in the late stance phase under the high-cadence condition. The TFL demonstrated sustained activation during the late swing phase in the high-cadence condition. Conclusions The present study suggests that phase-specific activation patterns in hip flexor muscles may be influenced by changes in step length and cadence, even when walking speed is held constant. The IL appears to contribute to step-length extension, while the RF and SA may play a role in swing initiation under high-cadence conditions. Sustained activation of the TFL during terminal swing may be associated with pelvic and lower limb control. Although based on a small and specific sample, these findings offer preliminary insights into neuromuscular control of gait and may serve as a useful reference for future studies, particularly those focused on age-related gait adaptations or interventions.