Characterization of an electric stimulation protocol for muscular exercise.

OBJECTIVE: The aim of this study is to evaluate the effect of rest time (ten minutes) on muscular strength production during a training session under electrical stimulation. PATIENTS AND METHODS: The isometric force output of the quadriceps femoris muscle was recorded during four sessions of stimulation of five minutes (15 maximal contractions: five seconds on and 15 seconds of rest), on 13 healthy adults. These four sessions are spaced out of ten minutes of recovery. The frequency of current is 100 Hz. RESULTS: At the 60th contraction, muscular force reaches 53 ± 7% of MVC. This value is significantly more important comparatively with a training session without rest time inside (27 ± 6% of MVC). CONCLUSION: The efficiency of electrical stimulation to improve muscle strength seems to be dependent on number of contractions per session with a high level of force production (> =60% de MVC). The protocol including intermediate periods of recovery seems more effective in order to produce a high level of force during all the training session.

Influence of electrical stimulation frequency on skeletal muscle force and fatigue.

OBJECTIVE: The aim of this study is to determine the impact of electrical stimulation frequency on muscle force and fatigue and propose application modalities in regards to sports or clinical rehabilitation training. METHODS: The maximal voluntary contraction (MVC) force of the quadriceps femoris muscle was recorded before, during and after electrical stimulation in 26 healthy adults during 20-minute sessions corresponding to 60 of 5-second contractions separated by 15-second rest periods. Three different frequencies were used: 100, 50 and 20 Hz. RESULTS: With a frequency of 100 Hz, we obtained 71% of the MVC force at the beginning of the session (MVCb). The decrease in muscle force at the end of the session is significantly greater for the highest frequencies respectively 27, 33 and 38% of MVCb for 100, 50 and 20 Hz. CONCLUSION: The impact of electrical stimulation to improve muscle force seems to be dependent on frequency, intensity pulse trains and number of contractions per session. Higher intensity and higher frequency induce stronger muscular contractions, but also a stronger decline in force and thus quick-setting muscle fatigue. Classical 20-minute training sessions with many contractions (60 or more) do not seem appropriate for sports training or clinical rehabilitation programs.