The purpose of this study was to determine the optimal frequency of electrical stimulartion, and compare a synergistic tension and sum of individual tension in the knee extensor of adult Sprague-Dawley rats. Individual branches of the femoral
nerve
supplying rectus femoris, vastus lateralis and vastus medialis were isolated underand operating microscope. Both ends of the femur were fixed using stainless steel pin to prevent movement of the femur during contraction of the knee extensor.
Mechanical
properties such as twitch and tetanic responses were recored by means of 3 iwsometric force transducers at 3 different directions including : extension, abduction and adduction. Individual tension and synergistic tension of 3 knee extensors were
elicited by individual and simultaneous electrical stimulation of 3 branches of the femoral nerve, respectively. Parameters of electrical stimulation for tetanic response wfer4 0.1 ms of pulse width, 1 V of amplitude and 20-60 Hz of frequency.
Results
of this experiment were as followings,
1. Optimal frequency of electrical stimulation was 40 Hz for knee kextensors.
2. Contraction time and fatigue resistance index knee extensors were 24.7 ms and 30.5%, respectively.
3. Synergistic tetanic tension was 114 g in knee extensors, which was lower than the sum of tetanic tension of individual knee kextensor.
4. There was no difference of tetanic tension between adduction and abduction of knee joint caused by tetanic contraction of vastus lateralis and vastus medialis.
These above results suggest that the knee extensor muscles have a characteristics of fast tswitch muscle and synergistic tension of agonistic muscle group induced by electrdical stimulattion is smaller than sum of individual muscle tension.
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