Changes in muscle activity of the gluteus medius and low-load training effects induced by skin cooling stimulus

Abstract

[Purpose] The purpose of this study was to investigate the effect of low-load training of the gluteus medius with skin cooling stimulus (SCS) on its muscle strength and activity. [Subects] The subjects were 32 healthy adult males with a mean age of 21.2 years. [Method] The subjects were divided into a SCS group and a control group, and carried out hip joint abduction exercises at a low load for 6 weeks. The maximum strength of isometric hip abduction and surface EMG of the gluteus medius were measured every other week. Integrated EMG and the mean power frequency were calculated at maximum isometric voluntary contraction (MIVC) and a load of 30% MIVC, and the results were normalized and compared with the values obtained at the start of the exercises. In addition, we measured subcutaneous skin thickness, and skin surface and deep tissue temperatures. [Results] MVIC significantly increased in the SCS group after 4 weeks of training in the SCS group. There was a significant increase in iEMG after 6 weeks of training, but no changes were found in mean power frequency. [Conclusion] We found low-load training of the gluteus medius with SCS had a significant muscle strengthening effect. We suggest exercise intensity, muscle activity characteristics of type I fibers and promotion of motor unit recruitment through skin cooling the muscle were reflected in the increase in muscle strength; however, we could not determine whether an increase in type II muscle fiber activity was involved.