Influence of vibration on endurance of maximal isometric contraction

Summary. In order to investigate how vibration affects endurance during muscular contraction, knee-joint extension efforts were performed with and without superimposed vibrations. Fourteen healthy non-smoking 20-year-old males performed maximal isometric and sustained knee-joint extension efforts (angle 90°) in sitting posture three times with each leg, with or without vibration. The tests were done once with each leg in a randomly chosen order. The frequency of the vibration was 20 Hz and the acceleration 20 m/s2 RMS, applied in a horizontal sagittal direction to the ankle. The endurance was defined as the time in seconds that it took for the exerted force to decrease by 10% of the initial value. The endurance time averages 22.5 s without vibration and 15.8 s with vibration. The vibratory stress reduced endurance by 6.7±1.84 s (mean ±SEM) (P<0.005). The difference in maximal force recorded initially was 34 ± 1.9 N (P<0.1). Our conclusion is that vibration may decrease the endurance of maximal och sustained isometric muscular contraction.