Detailed spatial characterization of superficial hip muscle activation during walking: A multi-electrode surface EMG investigation of the gluteal region in healthy older adults.

Purpose: A multi-electrode array was used to generate spatially resolved Surface electromyography (SEMG) data of the hip muscles in healthy older adults. The cohort was meant to serve as an age-matched, normal control population for future surgical and rehabilitative studies in patients undergoing total hip arthroplasty, in view of the large, continuously increasing number of hip joint replacements.

Methods: Bilateral hip muscle SEMG activity, including tensor fasciae latae (TFL), gluteus medius (Gmed), and gluteus maximus (Gmax), was measured during locomotion on a walkway at self-selected slow, normal, and fast walking speeds (age-matched cohort of 29 females and 25 males). Eight equally-spaced, vertically oriented bipolar channels were applied on a horizontal line at mid-distance between iliac crest and greater trochanter (length 17.5 cm; named P1 to P8). Time-independent parameters (e.g., mean amplitude) were derived from the amplitude curves expressed as root mean square.

Results: The acquired SEMG data were not significantly influenced by gender (p = 0.202) or side (p = 0.313) and were therefore pooled. The most ventral to central electrode positions P1 to P5, representing TFL and ventral to central Gmed, showed the highest mean amplitude levels (averaged over the whole stride; 0.001 < p < 0.027 against P6 to P8; Bonferroni-adjusted paired t-test) at all walking speeds. Also, the respective curves showed two distinct amplitude peaks (representing load acceptance and hip stabilization during mid-stance), with a continuous increase of the first peak from P1 to P4 (most pronounced at fast speed) and the second peak from P1 to P3. Independently of the underlying individual muscles, both peaks displayed a continuous time shift from the most dorsal P8 to the most ventral P1 position, with the peaks for the ventral positions occurring at later time points during the normalized stride.

Conclusions: The continuously changing activation patterns of the superficial muscles in the gluteal region during walking may reflect function-driven, finely tuned coordination patterns of neighboring muscles and muscle segments, rather than independent activation of anatomically defined muscles. This may be important for the definition of specific target parameters for the improvement and/or normalization of muscle function during training and post-injury rehabilitation.