4. Discussion
sarcopenia, increasing neuromuscular adaptations, skeletal muscle mass, muscle hypertrophy
CONTRACTIONS, SARCOPENIA, CONTRACTION, RECRUITMENT, CONTRACTED
EMS has been regarded as a bridge to conventional exercises. It has been postulated that EMS superimposed on voluntary contractions would have a significant impact on muscle strength and physical performance. More specifically, STEMS has been known to enhance motor unit recruitment of stimulated muscles, thereby increasing neuromuscular adaptations and motor control.EMS and conventional exercise induce different modes of muscle activation, resulting in different physiological effects and adaptations in the neuromuscular system. During voluntary contraction, motor units are recruited in sequential order from small to large, which is known as the size principle. Physiologically, synaptic currents activate motor unit recruitment, and smaller motor units tend to be activated more easily.In this study, we found that STEMS was superior to ST in terms of changes in core muscle thickness during voluntary contraction. Effective muscle hypertrophy was achieved in both the STEMS and ST groups based on muscle thickness at rest and during contraction. However, the contracted muscle thickness was more profound in the STEMS group, as measured by US. Contracted muscle thickness reveals a person’s ability to modulate each muscle during voluntary contraction.In this study, we further examined the effects of EMS on physical performance including isometric muscle power, complex whole-body dynamic activity, and core stability. The 2 training methods, STEMS and ST, improved the overall physical performance after training, but no significant difference was observed between the 2 groups. Improvements in functional movement are achieved not only by strength gains but also by the amelioration of various factors such as proprioception, peak torque, range of motion, and movement patterns.BIA is a practical method for assessing body composition, which allows the evaluation of core body components: fat mass, skeletal muscle mass, and water. The assessment of body composition using BIA has reached an outstanding position in studies in the fields of overall health care, nutrition, and athletic sports.The results of this study support the clinical effect of EMS on muscle activation. However, this study had several limitations. First, we only investigated the short-term effects of EMS during 8 weeks of intervention. We did not evaluate the long-lasting effects of ST and EMS on core muscle activation and physical performance. In addition, we only enrolled young healthy subjects, and therefore could not mention its effects on other populations, such as older patients with sarcopenia or other injuries. Lastly, this study only evaluated the physical performance under the isometric tests. Therefore, in-depth research regarding more dynamic values such as endurance, angular velocity, and complex coordination abilities is needed. Further studies with various populations and investigation of optimal EMS parameters, such as wave frequency and intensity, are needed to maximize the utility of EMS.