Effects of training intensity in electromyostimulation on human skeletal muscle

• Published in: European journal of applied physiology Vol. 118; no. 7; pp. 1339 - 1347
• Main Authors: Natsume, Toshiharu, Ozaki, Hayao, Kakigi, Ryo, Kobayashi, Hiroyuki, Naito, Hisashi
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.07.2018; Springer Nature B.V
• Subjects: Adult; Biomedical and Life Sciences; Biomedicine; Contraction; Electric Stimulation; Electrical stimuli; Human Physiology; Humans; Hypertrophy; Isometric Contraction; Knee; Leg; Leg - physiology; Male; Muscle Fibers, Skeletal - physiology; Muscle strength; Musculoskeletal system; Neuromuscular electrical stimulation; Occupational Medicine/Industrial Medicine; Original Article; Physical Conditioning, Human - methods; Quadriceps muscle; Skeletal muscle; Sports Medicine; Muscle fiber; Maximal voluntary contraction; Muscle thickness; Neuromuscular electrical stimulation
• ISSN: 1439-6319; 1439-6327
• DOI: 10.1007/s00421-018-3866-3

Purpose High-intensity neuromuscular electrical stimulation (NMES) training can induce muscle hypertrophy at the whole muscle and muscle fiber levels. However, whether low-intensity NMES training has a similar result is unknown. This study aimed to investigate whether low-intensity NMES training could elicit muscle hypertrophy at the whole muscle and muscle fiber levels in the human skeletal muscle. Methods Eight untrained young males were subjected to 18 min of unilateral NMES training for 8 weeks. One leg received NMES at maximal tolerable intensity (HIGH); the other leg received NMES at an intensity half of that in the HIGH condition (LOW). Quadriceps muscle thickness (MT), muscle fiber cross-sectional area (CSA), and knee extension strength were measured before and after the training period. Results The average training intensity throughout the intervention period in the HIGH and LOW conditions were 62.5 ± 4.6% maximal voluntary contraction (MVC) and 32.6 ± 2.6% MVC, respectively. MT, CSA, and muscle strength increased in both exercise conditions ( p  < 0.05); however, training effects in the LOW condition were lower than those in the HIGH condition ( p  < 0.05). The average training intensity showed a positive correlation with percent changes in muscle strength ( r  = 0.797, p  = 0.001), MT ( r  = 0.876, p  = 0.001), type I fiber CSA ( r  = 0.730, p  = 0.01), and type II fiber CSA ( r  = 0.899, p  = 0.001). Conclusions Low-intensity NMES could increase MT, muscle fiber CSA, and muscle strength in healthy human skeletal muscles. However, the magnitude of increase is lower in low-intensity than in high-intensity NMES training.