Muscle activity during multi-step descent

Previous step studies have shown mechanical variances across steps in descent; however, muscle activity differences have not been examined across steps in a staircase. The purpose of this study was to quantify differences in muscle activity during step descent between step strategies (step-over-step and step-match) and across steps.

Twenty-five individuals descended a seven-step staircase at self-selected pace (rise: 15.5 cm) in both descent types. Muscle activity was recorded with bipolar electrodes placed on the right tibialis anterior, peroneals, medial gastrocnemius, rectus femoris, and biceps femoris. Two-way Repeated Measures ANOVA tests were conducted for co-activation (ankle: tibialis anterior/medial gastrocnemius; knee: rectus femoris/biceps femoris) and integrated EMG in the lead and trail limbs.

Results showed muscle activity is dependent on the step number for both descent strategies.

Between strategies, lead limb step-match co-activation began the staircase high then decreased for both ankle and knee, while step-over-step activity was the opposite. Trail limb co-activation was more similar beginning high for both joints in step-over-step and the knee in step-match. Across steps, this study supports previous findings of differences between entry and exit steps compared to middle stairs. Additionally, differences were found between mid-staircase steps. These differences in both descent strategies counters previous assumptions of 'steady-state' step descent, which may have implications for individuals dealing with lower extremity musculoskeletal issues. Patients may benefit by training on their most encountered staircase length, and researchers must recognize the challenge of generalizing across step studies of varying step number.