Science & Research

Summary

The effects of hard squatting exercise with (VbX+) and without vibration exercise)) vibration on neuromuscular function were tested in 19 healthy young volunteers. Before and after the vibration exercise, three different tests were performed: maximum serial jumping for 30 s, electromyography during isometric knee extension at 70% of the maximum voluntary torque, and the quantitative analysis of the patellar tendon reflex. Between VbX+ and Vibration exercise) values, there was no difference found under

baseline conditions. Time to exhaustion was significantlyshorter in VbX+ than in VbX) but blood lactate and subjectively perceived exertion (rate of perceived exertion values 18Æ1 ± 1Æ2 versus 18Æ6 ± 1Æ6) at the termination of vibration exercise indicate comparable levels of fatigue. After the exercise, comparable effects were observed on jump height, ground contact time, and isometric torque. The vastus lateralis mean frequency during isometric torque, however, was higher after vibration exercise + than after Vbx. Likewise, the tendon reflex amplitude was significantly greater after Vb. It is followed that in exercise unto comparable degrees of exhaustion and muscular

fatigue, superimposed 26 Hz vibration appears to elicit an alteration in neuromuscular recruitment patterns, which apparently enhance neuromuscular excitability. Possibly, this effect may be exploited for the design of future training regimes.

Introduction

Although present in many classical sports, vibration loads have been neglected until very recently (Issurin et al., 1994; Mesteret al., 1999). Vibration exercise (VbX) is a new type of exercise, that has been designed with the idea of stimulating muscles via spinal reflexes. It is currently being tested in different fields, ranging from the training of elite athletes (Bosco et al., 1999) to the therapy of osteoporosis (Spitzenpfeil & Mester 1997; Rubin et al., 1998, 2001) and chronic low back pain (Rittweger et al., 2002b). Some unexpected observations have been made in the application of vibration exercise. For example, the blood volume has been reported to increase (Kerschan-Schindl et al., 2001), and an erythema may occur over the activated limbs (Rittweger et al., 2000). Another finding has been that of an increased electromyographic (EMG) median frequency inisometric contraction immediately after exhaustive vibration

exercise, which is in contrast to the general observation of a

decreased EMG frequency in muscle fatigue (Hakkinen & Komi

1983). It is evident that a better understanding of the physiolgical mechanisms involved in vibration exercise will help to identify the potential benefits of this technique. In this respect, an alteration in the neuromuscular functioning is of crucial interest. It was thus decided to investigate the acute neuromusclular effects of exhaustive whole body vibration in an integrative approach.

Procedures

Before starting, the subjects warmed up (10 min bicycling at

50 W and stretching). Whole body vibration exercise was

performed with a prototype of a commercially available product (Galileo 2000; NovoTec, Pforzheim, Germany). In brief, the device evokes platform oscillations around a central axis, that is located between both feet of the subject. Hence, the left and right leg are stretched and shortened alternatingly. The vibration amplitude was set to 6 mm (12 mm from top to bottom), and the frequency was set to 26 Hz.

During the exercise, squatting was performed from almost

complete extension of the knee to an angle of 90 . An additional load of 40% of the body mass was applied via a string that was attached to a hip belt. The length of the string was adjusted so that the weight touched the ground at flexions greater than 90 ,thus controlling the squatting range. For the temporal control of the squatting exercise, a metronome was set at 1 Hz, and the subjects were instructed to move 3 s down and 3 s up as evenly as they could. The precision of the movements was controlled by the experimenter confirming that the hanging weight almost

touched the platform during each squat cycle. Before and 2 min after all exercise bouts, the blood lactate was measured with the Accusport device (Roche Diagnostics, Mannheim, Germany), using capillary blood from the finger. During exercise, the rate of perceived exertion (RPE) was assessed every minute (Borg 1976). At the end of the exercise the subjects reported their level of fatigue. The load was then

discharged by a quick release button and the subject was placed on the chair or on the jumping plate, respectively. Testing began exactly 10 s after termination of the exercise.

Data analysis Signals from the contact plate, the hammer strain gauge, knee extension torque, and the electromyogram of the m. vastus lateralis were amplified and digitized with a 12-bit resolution and a sampling rate of 1000 Hz. The neuromuscular test variables were averaged over epochs of 10 s, yielding three consecutive epochs for each test condition

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