Science & Research

Abstract

The aim of this study was to evaluate the influence of vibration on the mechanical properties of arms of 12 international level boxers, all members of the Italian national team, voluntarily participated in the experiment: all were engaged in regular boxing training. At the beginning of the study they were tested whilst performing forearm ¯exion with an extra

load equal to 5% of the subjects' body mass. Following

this, one arm was given the experimental treatment (E;

mechanical vibration) and the other was the control (no

treatment). The E treatment consisted of (r)ve repetitions

lasting 1-min each of mechanical vibration applied

during arm ¯exion in isometric conditions with 1 min

rest between them. Further tests were performed 5 min

immediately after the treatment on both limbs. The

results showed statistically signi(r)cant enhancement of

the average power in the arm treated with vibrations.

The root mean square electromyogram had

not changed following the treatment but, when divided

by mechanical power, (P) as an index of neural e-

ciency, it showed statistically signi(r)cant increases. It

was concluded that mechanical vibrations enhanced

muscle P and decreased the related EMG/P relationship

in elite athletes. Moreover, the analysis of EMG

rms recorded before the treatment and during the treatment

itself showed an enormous increase in neural activity

during vibration up to more than twice the baseline

values. This would indicate that this type of treatment is

able to stimulate the neuromuscular system more than

other treatments used to improve neuromuscular

properties.

Key words Vibrations á Mechanical Power

Introduction

Introduction

The influence of resistance exercise on the neuromuscular properties of human skeletal muscles has been

studied over the years; as a result it has been observed

that, in response to such a stimulus, changes within the

muscle itself constitute the most important adaptation

(Sale 1988; Behm 1995). Neural adaptations have been

indicated as the (r)rst changes occurring in the muscle,

permitting gains in muscle strength and power in the

early stages of a resistance exercise programme in the

absence of increases in cross-sectional area of the muscle

(Behm 1995; Costill et al. 1979; Moritani and DeVries

1979). The (r)rst phase of adaptation has in fact been

universally attributed to an improvement in neural fac-

tors, the myogenic factors becoming more important as

the adaptations continue over several months (e.g.

McDonagh and Davies 1984). Research conducted on

the e�ects of resistance training have shown that speci(r)c

adaptations occur depending upon the training pro-

gramme employed (Sale and MacDougall 1981).

In this respect it is important to consider the impor-

tance of speci(r)city of training in producing particular

adaptations. When dealing with a sporting performance

such as the punch in boxing the aim of a resistance

training programme would need to be speci(r)c in im-

proving the segmental velocities of the arm, increasing in

this way the speed of this unloaded movement which is

the most important technical skill in boxing. Previous

studies have shown that training with heavy loads, with

low velocities of execution, primarily produces changes

in the force part of the force-velocity curve, while

training with light loads a�ects primarily the velocity

part (Kaneko et al. 1983). The mechanisms underlying

this e�ect of velocity speci(r)city have not been clearly

de(r)ned, most importance however has been given to

neural adaptations such as improved coordination, in-

creased activation of prime mover muscles (Moritani

and DeVries 1979), recruitment and synchronization.

It has been suggested that muscle stimulation by vi-

bration may induce improvements in the mechanical

power of the lower limbs in elite athletes (Bosco et al.

1998) through a neural adaptation. Moreover, Burke

et al. (1996) have shown that facilitation of the excit-

ability of the patellar tendon re�ex can be elicited

through vibration applied to the quadriceps muscle. It

has been shown that mechanical vibration (10�200 Hz)

administered to tendons or muscles can cause a re�ex

response (Hagbarth and Eklund 1965). This particular

re�ex activity has been named the ``tonic vibration re-

�ex''. It is still controversial as to whether it can be

elicited by low vibration treatment (30 Hz) or just from

frequencies of about 100 Hz and an amplitude of 1 mm

(Latash 1998), even if it has been suggested to occur

during whole body vibration at frequencies ranging from

1 to 30 Hz (Seidel 1988).

The aim of this study was to analyse the e�ects of

vibration on the neuromuscular behaviour of arm �ex-

ors in elite boxers and to gain knowledge from this to

verify its possible use as a means of training for improving explosive arm movements through an improvement of neuromuscular efficiency.

Method

A group of national level boxers (Italian national team) volun-

teered as subjects for the present study. All of them had been

competing for several years and were participating regularly in boxing training programmes. Full advice was given to the volunteers regarding the possible risk and discomfort that might be involved and all the subjects gave their written informed consent to participate in the experiment, which had been approved by the Ethics Committee of the Italian Society of Sport Science. Subjects with a previous history of fractures or bone injuries were excluded from the study. None of the subjects smoked and no medication

was being taken by the athletes which would have been expected to affect physical performance. Mechanical power measurements

Each subject was tested during forearm �exion with an extra load

equal to 5% of their body mass (mb). All the subjects performed a maximal dynamic elbow �exion with each limb. Five attempts were made with 1-min intervals between each. Since two or three trials

were needed to reach a plateau in performance, the last two trails of each set of measurements recorded from each limb were averaged and used for statistical analysis as has been recommended by Tornvall (1963) and Bosco et al. (1995). Both limbs were tested separately, with a 5-min interval between tests. After this evaluation, the arms were randomly assigned to receive the treatment (E)

or to be the control (C). After the vibration treatment both limbs were retested (post) using the same procedure as before (pre). During each elbow �exion, the mechanical power (P) was calculated, and electromyogram (EMG) activity was recorded from the biceps brachii muscle. The movement of the elbow �exion was monitored with a sensor (encoder) machine (MuscleLab�Bosco System, Ergotest Technology A.S., Langensund, Norway), interfaced to a personal computer

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