Development of Connective Tissue Area Increases by Initial Impact With High-Intensity Exercise After Reloading in Rat Soleus Muscle

ObjectiveThe aim of the study is to clarify whether high-intensity exercise in atrophied skeletal muscle after reloading (1) increases the injury and promotes the development of the muscle connective tissue area in the soleus muscle and (2) delays muscle strength recovery.DesignRats had their hindlimbs suspended for 14 days followed by hindlimb reloading and squat exercise of 30% or 70%-one-repetition maximum exercise until 14 days of reloading. The influences of reloading and exercise in muscles were examined by histological and immunofluorescence analyses based on the exercise load.ResultsSeventy percent-one-repetition maximum exercise increased the extramyofiber area more than the control group and the central nuclear fiber number than the other groups after 7 days of reloading. Seventy percent-one-repetition maximum exercise resulted in a larger muscle connective tissue area than the control and reload groups after 14 days of reloading. Myogenin and M2-type macrophages after 7 days of reloading increased by reloading but were not increased by the exercise load.ConclusionsSeventy percent-one-repetition maximum exercise to atrophied muscle increased injury early in postreloading and increased the muscle connective tissue area after 14 days of reloading, but evidence that it delays muscle strength recovery was lacking. Therefore, muscle connective tissue area induced by high-intensity exercise after reloading seems to be associated with initial exercise damage but not with repetition over 14 days.

Automated summary

The aim of this study was to investigate the effects of high-intensity exercise on atrophied skeletal muscle after reloading. The results showed that 70% one-repetition maximum exercise increased the extramyofiber area and central nuclear fiber number after 7 days of reloading, and also led to a larger muscle connective tissue area after 14 days of reloading. However, it was unclear whether this exercise delayed muscle strength recovery.