Strength response in human quadriceps femoris muscle during 2 neuromuscular electrical stimulation programs

Study Design: Experimental mixed repeated-measures design. Objective: To determine the effect of 2 versus 3 neuromuscular electrical stimulation (NMES) training sessions per week on the response to strength training of the quadriceps femoris muscle. Background: Many studies have examined the influence of training intensity (percent maximal voluntary isometric contraction [MVIC]) during NMES on the strength response of the quadriceps femoris muscle. However, no study has examined the effects of the number of NMES sessions per week on the change in strength of the quadriceps femoris. Methods and Measures: Twenty-seven healthy subjects (mean age+/-SD, 23.2+/-3.2 years) volunteered for the study and were randomly assigned to 1 of 3 groups; control group (no electrical stimulation); group 2 (NMES 2 times per week); and group 3 (NMES 3 times per week). Groups 2 and 3 received NMES (10 minutes per session) over a 4-week period for a total of 8 and 12 NMES training sessions, respectively. The isometric quadriceps femoris muscle force produced during NMES was monitored during each treatment minute. The MVIC force of the quadriceps femoris was assessed prior to the first week and at the start of weeks 2, 3, and 4 of the 4-week training program, with a final measurement after the fourth week (5 total measurements) for all subjects. Results: Only the mean percent change in quadriceps MVIC before and after the 4 weeks of training with NMES between the control group and group 3 was significantly different (P=.021). Conclusions: Based on the electrical stimulation parameters and healthy subjects used in this study, NMES caused significant increases in the quadriceps femoris muscle strength when used for 3 training sessions per week for 4 weeks. It is possible that the use of a different electrical stimulation paradigm and/or a different patient population may result in strength gains with 1 or 2 sessions per week.