How Does Localized Vibration Training (LVT) Work?
There are 5 main physiological mechanisms that are proposed at LV works to improve muscle performance during acute bouts. These are outlined below.
1. Tonic Vibratory Reflex Mechanism.
2. An increase in corticospinal excitability
3. A reduction in reciprocal inhibition.
4. Increase in Muscle Temperature
5. Increased Attentional Focus (Mind-Muscle Connection)
Tonic Vibration Reflex
When high-frequency vibration is applied to the muscle belly or its tendon, it elicits a reflex muscle contraction that has the potential to increase muscle function. Studies performed on the muscle– tendon site have reported a strong proprioceptive stimulus that elicits the primary somatosensory and motor cortices and influences the primary afferent firing rate.
Increased Corticospinal and Motor Neuron Excitability
This increase in force production during submaximal contractions can be attributed to an increase in corticospinal excitability (the strength of the response of cortical neurons to a given stimulation, reflects neuron reactivity) and has been demonstrated in both upper and lower limbs by an increase in motor evoked potential and lower resting motor threshold. This excitability seems to occur at different frequencies between muscle groups depending on muscle spindle density although this relationship seems to be inverted u shaped with too low or too high a frequency being sub-optimal. Too low a frequency provides insufficient temporal summation of Ia afferent discharge to lead to a change in corticospinal excitability and too high is an overstimulation of Ia afferents. The sweet-spot for most muscles based on optimal firing rate of Ia afferents seems to be between 50-110Hz. This increase in excitability seems to present whether the vibration is applied during contraction or at rest. Pulse therefore can be used as a priming exercise before performance.
Another reason for the improvement in muscle force is the reduction in excitability of the muscles that are opposing the movement (antagonists) and a longer cortical silent period in antagonist muscles. Muscle opposing the movements are turned off for longer. This is known as reciprocal inhibition and is a noticeable reason why we see an increase in strength early in training programs when muscles become better co-ordinated to produce movements.
Increase in Muscle Temperature
There has been a number of reports of increases in muscle temperature especially with WBV training attributing an increase of 0.3oC per minute of use, this is roughly double that of cycling (0.15oC per minute) and a hot bath (0.09oC per min). This was conducted using a Galileo machine (6mm amplitude, 26Hz Frequency) in the squatting position. This increase in muscle temperature can increase muscle force and contractility with increases in performance (2-5%) with every 1 degree increase in muscle temperature.
Mind-Muscle Connection (attentional focus)
Mind-muscle connection is a psychological aspect of training in which you focus on feeling each and every rep and recruiting specific muscles. It is about more than just going through the motions of each movement, but rather, focussing on a conscious and deliberate muscular contraction. This may particularly useful during rehabilitation in helping to re-train co-ordination patterns.
Attentional focus can be operationally defined as what an individual thinks about when carrying out a given movement or activity. There are two basic attentional focus strategies during performance of a task: internal and external. An internal focus involves thinking about a given bodily movement during performance while an external focus (i.e. pulse/LV) involves shifting performance- oriented concentration to the environment. In particular, this external focus has been demonstrated to show greater motor learning benefits.
All in all, the Pulse Device is the first LVT device that also incorporates attentional cues to help improve proprioception and the mind-muscle connection. It's a great tool for anyone trying to improve their performance or recovery.