Vibration Training and Human Performance

The improvement of the muscle performance after a short period of vibration training has been quoted (Bosco et al. 1998) to be similar to what occurs after several weeks of heavy resistance training (e.g. Coyle et al. 1981, Hakkinen and Komi 1985). In fact the improvement of the muscle functions after resistance training has been attributed to the enhancement of the neuromuscular behaviour caused by the increasing activity of the higher motor centre (Milner-Brownet al., 1975). The improvement of muscle performances induced by vibration training (VT) suggests that a neural adaptation has occurred in response to the vibration treatments. In this context, the duration of the stimulus seems to be both relevant and important. The adaptive response of human skeletal muscle to simulated hyper gravity conditions (1.1g) applied for only three weeks, caused a considerable improvement in the leg extensor muscle behaviour (Bosco 1985).

Thus it is likely that both neural adaptation and the length of the stimulus seem to play an important role in the improvement of muscle performances (e.g. Bosco, 1985). During the VT utilised for the research conducted on the boxers, the elbow flexors were stimulated for a total length of time of 300 seconds. The duration of the treatment was similar to that required to perform an elbow flexion for 600 repetitions with a load similar to 50/0 of the subject's body mass. Such an amount of repetitions would generally otherwise be distributed over 3 sessions a week with 50 repetitions per time, taking one month to complete. The large initial increases noted in muscle strength observed during the earlier weeks of intense strength training can be explained through increases in maximal neural activation (e.g. Moritani and De Vries, 1979). To explain how the increased neural output may occur is not as simple as how to explain the intrinsic mechanism of neural adaptation. Furthermore, a net excitation of the prime mover motoneurons could result from increased excitatory input, reduced inhibitory input or both (e.g. Sale, 1988).

After the VT period the EMG activity was found to be rather lower or to be the same as compared to the pre-treatment conditions even if, during the vibration, period an increment of neural input to the muscle occurred. In this respect the decrease in the ratio between EMG and mechanical power (EMG/P) demonstrated that VT induced an improvement of the neuromuscular efficiency of the muscles involved in the vibration treatment. Vertical jumping ability has been shown to increase following vibration treatment (Bosco et al. 1998; Bosco et al 1999). These improvements have been attributed to an enhancement of neural activity in the leg extensor muscles, together with an enhancement of the proprioceptors' feedback. During vibrations, the length of skeletal muscles changes slightly.

The facilitation of the excitability of spinal reflexes has been shown to be elicited by vibrations applied to the quadriceps muscle (Burke et al. 1996). Once again, the influence of vibrations on the neural drive of the la loop can play a crucial part in enhancing jumping performance following vibration treatments. Even if the adaptive responses of neuromuscular performance as measured by vertical jump tests cannot be fully explained, it is important to consider that the effectiveness of the stimulus can have both relevance and importance. The adaptive response of human skeletal muscle to simulated hyper gravity conditions (1.1 g), applied for only three weeks, caused a drastic enhancement of the neuromuscular functions of the leg extensor muscles (Bosco 1985). The regular use of centrifugal force (2 g) for 3 months has initiated conversion of muscle fibre type (Martin and Romond, 1975). In the experiments conducted, the total length of the WBV application period was not very long (from 7 minutes to 100 minutes), but the disturbance to the gravitational field was quite consistent (5.4 g).

An equivalent length and intensity of training stimulus (100 minutes) can only be reached by performing 200 drop jumps from 60 cm, twice a week for 12 months. In fact, the time spent for each drop jump is less than 200 ms, and the acceleration developed can barely reach 3.0 g (Bosco 1992). This means stimulating the muscles for 2 min per week for a total amount in one year of 108 minutes.
In a few words, vibrations can stimulate the biological system of athletes in the same way as strength training or explosive training and this stimulation can be applied in a much shorter period of time as compared to the time needed to perform traditional training sessions.