Riemann, BL, Limbaugh, GK, Eitner, JD, and LeFavi, RG. Medial and lateral gastrocnemius activation differences during heel-raise exercise with three different foot positions. J Strength Cond Res 25(3): 634-639, 2011-Despite little objective support, heel-raise exercises are commonly performed using varying foot positions in an attempt to alter medial (MG) and lateral (LG) gastrocnemius involvement. This investigation compared MG and LG activation during the concentric phase (CP) and eccentric phase (EP) of the heel-raise exercise using neutral (NE), internally rotated (IR), and externally rotated (ER) foot positions. Twenty healthy subjects (10 men, 10 women; age = 23.7 ± 3.1 years) with resistance training experience performed free-weight (130-135% body mass) heel-raise exercise on a 3.81-cm block. Surface electromyography activity was recorded during 10 repetitions of each foot position. Electromyography activity from 5 successful repetitions was normalized to maximum voluntary isometric contraction, ensemble averaged within phase (CP, EP), and the mean amplitude determined. Significant (p < 0.05) muscle-by-foot position interactions were revealed for both phases. The ER position prompted significantly greater MG activation than LG during both phases, whereas the IR position elicited significantly greater LG activation than MG. These data support the notion that altering foot position during heel-raise exercise will prompt varying degrees of MG and LG activation. Although this study cannot predict whether muscle-activation differences between foot positions will translate into greater training adaptations, it does provide some initial objective evidence upon which practitioners can base the selection of gastrocnemius exercises.