Strength Increase after Whole-Body Vibration Compared with Resistance Training

Abstract

The aim of this study was to investigate and to compare the effect of a 12-wk period of whole-body vibration training and resistance training on human knee-extensor strength.

Methods

Sixty-seven untrained females participated in the study. The whole-body vibration group (WBV) and the placebo group performed static and dynamic knee-extensor exercises on a vibration platform. The acceleration of the vibration platform was between 2.28 g and 5.09 g, whereas only 0.4 g for the PL condition. Vibration (35- 40 Hz) resulted in increased EMG activity, but the EMG signal remained unchanged in the PL condition. The resistance-training group trained knee extensors by dynamic leg-press and leg-extension exercises

The control group did not participate in any training. Pre- and postisometric, dynamic, and ballistic knee-extensor strength

were measured by means of a motor-driven dynamometer. Explosive strength was determined by means of a counter-movement jump.

Results

Isometric and dynamic knee-extensor strength increased significantly in both the WBV group respectively, whereas the PL and CO group showed no significant increase. Counter-movement jump height enhanced significantly in the WBV group only. There was no effect of any of the interventions on maximal speed of movement, as measured by means of ballistic tests. Conclusions: WBV, and the reflexive muscle contraction it provokes, has the potential to induce strength gain in knee extensors of previously untrained

females to the same extent as resistance training at moderate intensity. It was clearly shown that strength increases after WBV training are not attributable to a placebo effect. Key Words: MUSCLE STRENGTH, TONIC VIBRATION REFLEX, COUNTER-MOVEMENT JUMP, STRENGTH TRAINING

from the vibration induced muscle activation. Additionally,

there are no studies available to compare the effect of WBV

and resistance training on muscle strength.

This is the first long-term study to differentiate between

the effects resulting from the exercises performed on the

platform with vibration and without vibration (placebo) and

to compare the effects of WBV training and resistance

training by means of weight machines at moderate intensity.

Therefore, the changes in isometric, dynamic, ballistic knee-

extensor strength, and counter-movement jump (CMJ)

height were analyzed in young female adults after a 12-wk

training period.

As WBV elicits a high degree of muscle activation, it was

hypothesized that WBV would result in strength increase in

previously untrained persons. These strength increases

should be significantly larger than the training effects re-

sulting from an identical exercise program performed in

absence of vibration (placebo condition). As the tonic vi-

bration reflex facilitates the activation of high-threshold

motor units and the reflex sensitivity (1,18), WBV training

may be more efficient to improve ballistic strength and jump

performance compared with resistance training at moderate

intensity.

Methods

Experimental Approach to the Problem

A four group prepost design was used in this study to

determine whether a 12-wk period of WBV-training (3

times/wk) would result in a considerable increase in knee-

extensor strength, and whether WBV training, compared

with moderate resistance training, would be more efficient

to improve ballistic and explosive strength in previously

untrained subjects. The four groups included a WBV group,

a resistance-training group, a control group, and a placebo

group. This latter group was added to determine whether the

expected training effect in the WBV group resulted from the

exercises that are performed on the platform or from the

vibration induced muscle activity. Isometric strength, dy-

namic strength, and ballistic strength of the knee extensors

were measured in pre- and post-test conditions. Explosive

strength was measured by means of a CMJ.

Subjects and Study Design

A group of 74 young female adults volunteered to participate in the study. None of them were engaged in regular organized physical activities nor in sports or strength training. Reasons for exclusion were pregnancy, acute hernia, and any history of severe musculoskeletal

problems. Subjects with a history of diabetes or epilepsy

were also excluded from the study. All subjects were in-

formed about the training and test protocol and about the

possible risks and benefits of the study. They all gave

written informed consent to participate. This study was

approved by the University's Human Ethics Committee

according to the declaration of Helsinki.

Power analysis revealed that a sample size of 17 subjects

in the experimental groups was necessary to achieve a

power of 0.80 with

0.05. In anticipation of inevitable

dropout, it was decided to select a minimum of 20 subjects

in the experimental groups.

Whatever may be the mechanisms behind it, it is clear

that WBV elicits muscle contraction involuntary and it

induces strength gain in previously untrained subjects

within a short period of time and without much effort. The

subjects did not experience the WBV training as exhausting

training sessions. This suggests that WBV has a great po-

tential in a therapeutic context where it may enhance mus-

cular performance in patients and elderly, who are not

attracted to or who are not able to perform standard exercise

programs. It may also enhance performance of athletes in a

stretch-shortening cycle, as suggested by the results on the

CMJ.

Conclusion

This is the first study that demonstrates that

the stimulation of propriospinal pathways provoked by

WBV and the resulting increase in muscle activity have the

potential to induce strength gain in the knee extensors of

previously untrained subjects to the same extent as resis-

tance training at moderate intensity. The findings of this

study clearly indicate that strength increases after 12 wk of

WBV training are not attributable to a placebo effect. The

CMJ height increased significantly in the WBV group only.

The results of this study suggest that strength increases

recorded in the WBV group are mainly resulting from neural

adaptations and can be ascribed to a more efficient use of

sensory information in the production of force. It is clear

that more research on WBV is needed to clarify the mech-

anisms of muscle contractions and strength gain.

This research was technically supported by Power Plate

(r)

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