Medial And Lateral Gastrocnemius Activation Differences During Heel Raise Exercise With Three Different Foot Positions

Abstract

Instructional guidelines from some national exercise certification organizations recommend performing heel raise exercise with varying initial foot positions to alter the involvement of the gastrocnemius' medial (MG) or lateral (LG) head. PURPOSE: To compare MG and LG activation during the concentric (CP) and eccentric (EP) phases of heel raise exercise using neutral (N), internally-rotated (IR) and externally-rotated (ER) foot positions. The term "foot position" was maintained for consistency with instructional texts, though the initial foot position reflects hip rotation. METHODS: Twelve healthy subjects (9 male, 3 female; 24.0 ± 3.8yrs) with resistance training experience performed free-weight (bar loaded to 30% body mass) heel raise exercise on a 3.8 cm block. Surface electromyographic (EMG) activity was recorded during five repetitions under each of the N, IR and ER foot positions, divided into CP and EP phases, and ensemble averaged within phase. Mean EMG amplitude, normalized to maximum voluntary contraction, was calculated. Separate two-factor (position by head) repeated measures analysis of variance were used for each phase. Simple main effects post hoc analyses of the significant (P <.05) interactions were conducted. RESULTS: During EP, significantly greater MG activity compared to LG activity was revealed for both N and ER. During CP, significantly greater LG activity compared to the MG occurred for IR. Further, post hoc analyses on the EP revealed that MG activity using ER was significantly greater than MG activity using IR or N. Likewise, analysis of CP revealed that LG activity using IR was significantly greater than LG activity using ER or N. CONCLUSION: Altering foot positions during the heel raise exercise does alter relative muscle activation as measured by surface EMG. The MG is activated to a significantly greater extent than the LG during EP using N and ER, while the LG displays significantly greater muscle activity than the MG during CP using IR. Further research is recommended to elucidate the role of the contraction phases in these differences.