Effects of Combination Therapy of Heat Stress and Muscle Contraction Exercise Induced by Neuromuscular Electrical Stimulation on Disuse Atrophy in the Rat Gastrocnemius

[Purpose] We investigated the effect of combination therapy, consisting of heat stress and muscle contraction exercise induced by neuromuscular electrical stimulation (NMES), for the prevention of hindlimb suspension (HS)-induced disuse atrophy in rat gastrocnemius (GAS) muscles, and clarified the effective exercise intensity for this therapy. [Methods] The experimental group was divided into the following six groups: 1) HS only; 2) HS plus heat stress (Heat); 3) HS plus low-intensity exercise (LEx); 4) HS plus combination therapy of heat stress and low-intensity exercise (H+LEx); 5) HS plus high-intensity exercise (HEx); and 6) HS plus combination therapy of heat stress and high-intensity exercise.(H+HEx). Before, and at the end of the experimental period, muscle wet. weight relative to total body weight, muscle fiber diameter, and heat shock protein (Hsp) 72 content in GAS muscles were evaluated. [Results] In the H+LEx and HEx groups, atrophy of all muscle fiber types in the deep and superficial regions was prevented. Hsp 72 expression was upregulated in the Heat, H+LEx, and H+HEx groups. [Conclusion] Our results suggest that low-intensity exercise is more effective than high-intensity exercise for the prevention of disuse muscle atrophy using heat stress and exercise combination therapy. The expression of Hsp72, which is induced by heat stress, may be related to this preventative mechanism.