Specific Changes in Contractile Functions and Skeletal Muscle Architecture in Humans in Response to the Use of Two Protocols of Unmodulated Neuromuscular Electrical Stimulation

The purpose of this study was to evaluate the effect of unmodulated low-frequency superficial neuromuscular electrical stimulation (NMES) for 30 and 60 min/day during 7 weeks on muscle contractile functions. Many studies have examined the effect of training intensity during NMES on maximal voluntary isometric strength (MVIS). However, no study has assessed the effect of NMES duration per day and per week on changes in muscle functions. Ten healthy volunteers (23.2 ± 3.2 years; age range 18–28 years) participated in the study and were randomly assigned to group 1 (30 min NMES) and group 2 (60 min NMES) five times a week. The influence of NMES training was estimated by changes in MVIS and speed-strength properties of foot extensors before electrical training and in the beginning of each week of a 7-week training period for all subjects. Contractile abilities were recorded with a Biodex isokinetic dynamometer. After a 7-week training period, MVIS and voluntary maximal explosive strength differed significantly between groups. Referring to electrical stimulation parameters and healthy subjects of this study, electrical training caused an increase in foot extensor muscle strength and a gradient in voluntary explosive strength when used for five trainings per week for 30 min for 7 weeks.