Human soleus muscle protein synthesis following resistance exercise

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Abstract
Aim: It is generally believed the calf muscles in humans are relatively unresponsive to resistance training when compared with other muscles of the body. The purpose of this investigation was to determine the muscle protein synthesis response of the soleus muscle following a standard high intensity bout of resistance exercise. Methods: Eight recreationally active males (27 ± 4 years) completed three unilateral calf muscle exercises: standing calf press/heel raise, bent-knee calf press/heel raise, and seated calf press/heel raise. Each exercise consisted of four sets of 15 repetitions (∼15 repetition maximum, RM, or ∼70% 1RM). Fractional rate of muscle protein synthesis (FSR) was determined with a primed constant infusion of [2H5]phenylalanine coupled with muscle biopsies immediately and 3 h following the exercise in both the exercise and non-exercise (resting control) leg. Results: FSR was elevated (P < 0.05) in the exercise (0.069 ± 0.010) vs. the control (0.051 ± 0.012) leg. Muscle glycogen concentration was lower (P < 0.05) in the exercise compared with the control leg (Decrease from control; immediate post-exercise: 54 ± 5; 3 h post-exercise: 36 ±4 mmol kg−1 wet wt.). This relatively high amount of glycogen use is comparable with previous studies of resistance exercise of the thigh (i.e. vastus lateralis; ∼41–49 mmol kg−1 wet wt.). However, the exercise-induced increase in FSR that has been consistently reported for the vastus lateralis (∼0.045–0.060% h−1) is on average ∼200% higher than reported here for the soleus (0.019 ± 0.003% h−1). Conclusions: These results suggest the relatively poor response of soleus muscle protein synthesis to an acute bout of resistance exercise may be the basis for the relative inability of the calf muscles to respond to resistance training programs.

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