Summary

Occupationally used high-frequency vibration is supposed to have negative effects on blood flow and muscle strength. Conversely, low-frequency vibration used as a training tool appears to increase muscle strength, but nothing is known about its effects on peripheral circulation. The aim of this investigation was to quantify alterations in muscle blood volume after whole muscle vibration ± after exercising on the

training device Galileo 2000 (Novotec GmbH, Pforzheim, Germany). Twenty healthy adults performed a 9-min standing test. They stood with both feet on a platform, producing oscillating mechanical vibrations of 26 Hz. Alterations in muscle blood volume of the quadriceps and gastrocnemius muscles were assessed with power Doppler sonography and arterial blood flow of the popliteal artery with a Doppler ultrasound machine. Measurements were performed before and immediately after exercising. Power Doppler indices indicative of muscular blood circulation in the calf and thigh signi(r)cantly increased after exercise. The mean blood flow velocity in the popliteal artery increased from 6á5 to 13á0 cm s ±1and its resistive index was signi(r)cantlyreduced. The results indicate that low-frequency

vibration does not have the negative effects on peripheral circulation known from occupational high-frequency vibration.

Keywords: arterial blood flow, muscle contraction,tissue blood flow, vibration.Introduction As early as in 1949, Whedon et al. (1949) reported the positive effect of passive exercise, by means of an oscillating bed, on metabolic abnormalities in plasterimmobilized patients. In an experimental study it has been shown that the application of 50 Hz, 10 g vibration for 2±5 h daily increased the cross-section of muscle (r)bres and reduced the fat content of muscle tissue (Hettinger, 1956). A randomized study showed

that, in athletes, 3 weeks of strength training (sitting benchpress) with superimposed vibratory stimulation

led to an almost 50% increase in the one-repetition maximum compared with an average gain of 16%

with conventional training and no gain for the control

group (Issurin et al., 1994). On the other hand, investigating forestry operators, Bovenzi et al. (1991) showed that a loss in grip strength may occur after prolonged occupational vibration exposure. Workers who use hand-held vibrating tools may also experience (r)nger blanching attacks as a result of episodic vasospasm in the digital vessels (Bovenzi & Grif(r)n, 1997). An experimental study with rats attached to a

vibrating table.

The power Doppler sonography technique allows quanti(r)cation of relative moving blood volume (Rubin et al., 1995). MR imaging and conventional colour Doppler imaging correlate well with other physiological measures of exercise-induced changes in blood flow (Hirsch et al., 1995; Pena et al., 1996). Fleckenstein et al. (1988) showed that a few minutes of muscle activity led to signal intensity changes on

MR images, which correlated moderately with the level of exertion. When standing on a vibrating platform, one tends

to attenuate the imposed vibration and misalignment

of stance by physical activity. The rhythmic muscle contractions evoked by standing on a vibrating platform may be bene(r)cial in counteracting the lack of other physical exercise, but its effects on peripheral circulation are not thoroughly examined yet. So far, most studies investigating the effect of vibration on blood ¯ow have used frequencies

common among tools used in industry which generally means 80±100 Hz (LundstroÈm & BurstoÈm, 1984).

In this study this range of frequency is summarized as `high frequency' and frequencies below that are called`low frequency'. A comparison of different magnitudes

Subjects

Healthy volunteers between 25 and 35 years of age were allowed to participate in the study. With respect to regular physical activity they were required not to have a sedentary lifestyle but also not to engage in regular strenuous physical activity, especially weightlifting exercises. Informed consent was given by all participants and the protocol conformed to the Declaration of Helsinki.

Training

Prior to the experiment, the subjects' age, height and weight were recorded. The level of regular occupational and recreational physical activities were assessed according to the American Heart Association (1975). The subjects were exposed to whole-body vibration using the Galileo 2000 device (Novotec GmbH, Pforzheim, Germany). They stood on a platform (r)xed on a sagittal axle which alternately pushes the right and left leg upwards and downwards at a frequency

of 26 Hz (amplitude ˆ 3 mm, peak acceleration ˆ 78 m s)2

). Three sets of different positions were used. During the (r)rst set, the subjects stood with their legs straight and their forefeet parallel to each other on the platform. The second bout was performed with the entire feet standing on the platform and moderately (60±70°) bent knees. Position 3 was the same as position 2 but the legs were rotated externally by about 30° and the knees were bent by about

60±70°. Each of the three positions was held for 3 min and

the exercise was continued without break between the positions. Thus, the total work out was 9 min. The subjects stood barefoot in order to avoid footware-dependent attenuation of the vibrations. To avoid biorhythmic changes, all subjects performed the experiment at the same time of the day between 10 a.m. and 12 p.m.

Outcome measurements

Heart rate was monitored with suitable devices (Polar beat, Polar Electro Oy, Kempele, Finland) and blood pressure was measured using conventional mano-meter technique (Heintel Rudolf, GesmbH, Vienna, Austria). Using a diagnostic ultrasound machine (Ultramark 9, ATL Advanced Technology Laboratories, Inc., Bothell, WA, USA) with colour Doppler

and power Doppler, relative moving blood volume was quanti(r)ed according to Newman's method (Newman et al., 1997). During the measuring procedure the subjects were standing. First, measuring Vibration exercise ± muscle blood volume K. Kerschan-Schindl et al.

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