Abstract
It has been proposed that superior muscle hypertrophy may be obtained by training muscles predominant in type I fibers with lighter loads and those predominant in type II fibers with heavier loads.PurposeTo evaluate longitudinal changes in muscle strength and hypertrophy of the soleus (a predominantly slow‐twitch muscle) and gastrocnemius (muscle with a similar composition of slow and fast‐twitch fibers) when subjected to light (20–30 repetition maximum) and heavy (6–10 repetition maximum) load plantarflexion exercise.MethodsThe study employed a within‐subject design whereby 26 untrained young men had their lower limbs randomized to perform plantarflexion with a low‐load (LIGHT) and a high‐load (HEAVY) for 8 weeks. Muscle thickness was estimated via B‐mode ultrasound and maximal strength was determined by isometric dynamometry.ResultsResults showed that changes in muscle thickness were similar for the soleus and the gastrocnemius regardless of the magnitude of load used in training. Furthermore, each of the calf muscles demonstrated robust hypertrophy, with the lateral gastrocnemius showing greater gains compared to the medial gastrocnemius and soleus. Both HEAVY and LIGHT training programs elicited similar hypertrophic increases in the triceps surae. Finally, isometric strength increases were similar between loading conditions.ConclusionsThe triceps surae muscles respond robustly to regimented exercise and measures of muscle hypertrophy and isometric strength appear independent of muscle fiber type composition. Moreover, the study provides further evidence that low‐load training is a viable strategy to increase hypertrophy in different human muscles, with hypertrophic increases similar to that observed using heavy loads.
Highlights
Human skeletal muscle is composed of two primary types of fibers: type I and type II
Similar findings were observed in the lateral gastrocnemius (LG), which exhibited a difference between LIGHT and HEAVY that was 0.02 SDs greater than the soleus (Figure 2a)
Our findings cast doubt on the claim that training muscles based on their fiber composition provides an additional benefit for enhancing muscle strength or hypertrophy
Summary
Human skeletal muscle is composed of two primary types of fibers: type I and type II. Type I fibers possess endurance-oriented properties, with slow times to peak tension and a high-capacity to resist fatigue (Talbot & Maves, 2016). The soleus is composed almost entirely of type I fibers (~80%) whereas the gastrocnemius has a similar composition of both fiber types (Elder, Bradbury, & Roberts, 1982; Gollnick, Sjodin, Karlsson, Jansson, & Saltin, 1974; Johnson, Polgar, Weightman, & Appleton, 1973). This is consistent with the functional role of the respective muscles. The primary role of the soleus is to help sustain posture in the standing position; alternatively, the gastrocnemius has more of a phasic role in carrying out explosive movements at the ankle joint (Vandervoort & McComas, 1983)
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