Introduction
Vibration stimulation is gaining popularity as a neuromuscular training method with the potential to elicit muscular performance adaptations similar to those produced by explosive strength training. Studies on vibration have shown transient increases in muscle power output and chronic strength enhancement and significantly improved gait and body balance in elderly people. In addition, whole body vibration induced positive adaptations in peripheral blood circulation (increased blood volume and speed of blood flow), probably due to decreased blood viscosity and peripheral resistance and arterial vasodilatation. Additionally, vibration has the potential to activate large amounts of musculature during a movement, and appears to inhibit activation of antagonist muscles which would decrease the braking force during a movement. Other studies have shown that vibration may be able to
influence the excitatory state of the peripheral and central structures of the brain, which could facilitate subsequent voluntary movements.
Targeted Vibration Training
Due to the conflicting results and potential side-effects of whole-body vibration, applying the vibration directly to the exercising muscle only has demonstrated performance gains more than 300% greater than conventional training. Therefore, researchers Dr Mileva and Dr Bowtell hypothesised that vibration applied during a single resistance-training session would promote larger acute increases in strength than those induced by an identical session performed in the absence of vibration. It was further hypothesized that vibration stimulus would provoke a greater response when training at lower contraction intensity, where a smaller percentage of muscle fibers would be voluntarily activated. To accomplish this, researchers compared the acute effects of vibration stimulus during and after high- (70% of one-repetition maximum (1RM) and low intensity (35% 1RM) knee extension exercise.
Methods
Nine healthy male adults completed four trials on a knee extension machine (Technogym UK Ltd) either with (Vibrex, Exoscience Ltd) or without superimposed vibration at low (35% 1RM) and high (70% 1RM) contraction intensities.
Results
The main finding of the study was that vibration applied during knee extension exercise improved the mechanical performance of the quadriceps muscles, as manifested by increased dynamic muscle strength and power. Additionally, peak torque was significantly higher during the vibrated than the nonvibrated trials.
The improvement in strength and power after vibration training could be explained by the finding that the median frequency of the quadriceps muscle electrical activity was significantly higher in the vibrated than nonvibrated trials. This suggests that vibration increases muscle fiber conduction velocity and/or increased recruitment of muscle fibers with faster conduction velocities such as fast powerful muscle fibres.
A very novel finding from this study is that superimposing the vibration-like stimulus during low-intensity exercise simulates the response induced by higher-intensity exercise, evidenced by increased electrical activity in the quadriceps muscle.
The increase in contraction force implies that reflex feedback from the muscle receptors in contracting muscle is increased. One might expect such increases in exercising muscle activation level to elevate the oxygen requirement, and vibration tended to increase the rate of muscle deoxygenation during exercise, which is indicative of increased oxygen utilization.
Conclusions
Neural adaptations are the earliest changes that occur in the exercised muscle (first 3–5 wk of a training
program), permitting gains in strength and power without significant increase in muscle cross-sectional area. The acute enhancement of neuromuscular performance following vibration is probably related to an increase in the sensitivity of the stretch reflex. This would result in more rapid activation and training of a larger number of high-threshold motor units. Vibration-induced discharge of the muscle receptors also recruits previously inactive motor units into the contraction, as well as re-recruiting motor units that are already fatigued, and even increasing their firing patterns.
It is also an intriguing possibility that a chronic vibration training program may potentially increase the neuromuscular adaptations arising from light/moderate training. This would be of importance for individuals, such as the elderly, osteoporosis and rehabilitation where people are unable to complete more intense exercise programs.
Monday, 17 December 2007
Tuesday, 4 December 2007
Breathing vibration - can it make us stronger?
Introduction
Acute vibration stimulation enhances skeletal muscle activity and strength performance (Issurin & Tenenbaum, 1989; Bosco et al., 1999; Mileva et al., 2006). Vibration stimulation has also been applied to the respiratory musculature with demonstrable increases in respiratory activity in rabbits (Jammes et al., 2000), reduced breathlessness at rest in healthy humans (Edo et al., 1998), and reduced breathlessness during exercise in chronic obstructive pulmonary disease patients (Fujie et al., 2002).
We therefore investigated whether a vibration stimulus applied through air as it passes into the airways elicits increments of maximal breathing performance.
Methods
We recruited 12 healthy subjects (8 female, 4 male; 22-50 years old) from the University and they completed 3 maximal inspirations followed by 10 inspirations against a vibration stimulus (VIB; youbreathe, Exoscience Ltd., London, UK), an inspiratory resistive-load training device (RES) or resting breathing (CON; no load). 3 forced inspirations were repeated and compared to pre-training for maximal breathing power.
Results
Maximal breathing power was significantly greater (15%) after 10 breaths of vibrated resistance (VIB) when compared to PRE (VIB) and POST control (CON) and POST resistive-loading training device (RES). There was no effect of either resistance or control breathing on maximal breathing power.
Discussion
10 breaths of vibration lead to increased maximal breathing power suggesting that applying a vibration stimulus increases the voluntary force generating capacity of the inspiratory muscles, in a similar manner observed when vibration is applied to other skeletal muscles (Mileva et al., 2006).
The mechanisms underlying the changes in maximal breathing power require further study, however mechanisms such as shifts in neuromuscular recruitment via increases in stretch reflex sensitivity may have a role (Cardinale, 2003). This would enhance recruitment of higher-threshold motor units and the activation of previously inactive motor units. Confirmation of the mechanisms involved will require the acquisition of respiratory muscle EMG, transcranial magnetic stimulation and testing of peripheral reflexes.
Thus, vibration leads to an increased maximal breathing power suggesting there is an increase in neural inspiratory drive possibly via upregulation of the respiratory motoneurones.
Acute vibration stimulation enhances skeletal muscle activity and strength performance (Issurin & Tenenbaum, 1989; Bosco et al., 1999; Mileva et al., 2006). Vibration stimulation has also been applied to the respiratory musculature with demonstrable increases in respiratory activity in rabbits (Jammes et al., 2000), reduced breathlessness at rest in healthy humans (Edo et al., 1998), and reduced breathlessness during exercise in chronic obstructive pulmonary disease patients (Fujie et al., 2002).
We therefore investigated whether a vibration stimulus applied through air as it passes into the airways elicits increments of maximal breathing performance.
Methods
We recruited 12 healthy subjects (8 female, 4 male; 22-50 years old) from the University and they completed 3 maximal inspirations followed by 10 inspirations against a vibration stimulus (VIB; youbreathe, Exoscience Ltd., London, UK), an inspiratory resistive-load training device (RES) or resting breathing (CON; no load). 3 forced inspirations were repeated and compared to pre-training for maximal breathing power.
Results
Maximal breathing power was significantly greater (15%) after 10 breaths of vibrated resistance (VIB) when compared to PRE (VIB) and POST control (CON) and POST resistive-loading training device (RES). There was no effect of either resistance or control breathing on maximal breathing power.
Discussion
10 breaths of vibration lead to increased maximal breathing power suggesting that applying a vibration stimulus increases the voluntary force generating capacity of the inspiratory muscles, in a similar manner observed when vibration is applied to other skeletal muscles (Mileva et al., 2006).
The mechanisms underlying the changes in maximal breathing power require further study, however mechanisms such as shifts in neuromuscular recruitment via increases in stretch reflex sensitivity may have a role (Cardinale, 2003). This would enhance recruitment of higher-threshold motor units and the activation of previously inactive motor units. Confirmation of the mechanisms involved will require the acquisition of respiratory muscle EMG, transcranial magnetic stimulation and testing of peripheral reflexes.
Thus, vibration leads to an increased maximal breathing power suggesting there is an increase in neural inspiratory drive possibly via upregulation of the respiratory motoneurones.
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