Abstract
Optimal rest intervals required between contractions and treatment sessions to allow recovery from fatigue after electrical stimulation of muscle are not known. In eight volunteers (aged 23-38 years), fatigue of the quadriceps was examined during and after three therapeutic stimulation protocols which were performed one week apart. Protocols consisted of 10 isometric contractions at 30% maximum voluntary force. The contractions lasted 10 seconds each, and were separated by rests of either 10, 50 or 120 seconds. Force responses to stimulation at 20 Hz and 50 Hz (for two seconds each) were used as a test to monitor recovery.
All three therapeutic stimulation protocols caused significant fatigue during activity. The shorter the rest interval, the greater the fatigue and hence, less work (i.e. integrated force) completed. Recovery was also influenced by the rest intervals. One hour after activity, force at 20 Hz was approximately 50% of initial values (p < 0.01), increasing to 70-80%at 24-hours, and to 90% at 48-hours. Force at 50 Hz was 68-80% after the first hour, had recovered 24-hours after the 10 second protocol but not the 50 and 120 second protocols, and full recovery had been reached by 48-hours. Persistence of both high and low frequency fatigue after these therapeutic protocols was greater than expected. Studies are required to determine whether stimulation of fatigued muscle produces therapeutic or adverse effects, and to establish the degree of recovery required for these effects.
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