Can Random Signal and Noise (Stochastic Resonance) Improve Human Function and Athletic Performance?

>> November 26, 2016

For this unique topic, the best for me to start is by explaining how vibration can improve athletic performance.

I think that the Soviet coaches and scientists were the first to use vibration as a means to improve functional movements or even athletic performance. This could be traced back in the 1960s, when coaches in the Eastern Bloc started to use "contraction" type exercises such as oscillation training in their training ("secretly") to gain performance advantage in different circumstances (e.g. rehabilitation, normal training, conditioning).

Oscillation training involves a powerful muscular contraction, which enhances muscular strength and power. So this is basically sort of "vibrating the muscle" areas under tension (loaded) you wish to develop, or so.

Fast forward, in the 1980s, Vladimir Nazarov assessed the feasibility of vibration to maintain strength and muscle mass among cosmonauts. The reason for this was when in space, the reduced gravitational force might affect bone density, strength, and muscle mass. As a result, cosmonauts might be susceptible to having bone fractures, muscle atrophy, and weakening of strength very quickly upon returning to earth.

It is not practical to have "gym" in space and what can possibly be done is to use vibration for the said purposes. This way the duration of stay in space could be extended as well.
The commercially available vibratory platforms, and their types of vibration, from left: Power Plate (sine wave), Galileo (sine wave), and SRT (stochastic resonance)

Effects of vibration on performance

Vibration has been used to elicit a stretch reflex in the muscles in order to "potentiate" the following performance. Of note, any preconditioning stimulus (such as using heavy resistance as well as vibration) could have the potential to improve subsequent tasks (performance). This is called "post-activation potentiation".

More recently, a training study provided evidence supporting the suitability of vibration training (Perez-Turpin et al., 2014). The authors described its effectiveness that provided rapid gains in performance, more than conventional training (i.e. increased leg strength and jump performance in 6 weeks).

According to the authors ... activation of muscle spindles from vibration could stimulate alpha motor neurons and promote stretch reflexes. They further clarified that long-term vibration training gained via neural adaptation was similar to the effects of resistance training, that is the enhancement of motor unit firing, motor unit synchronization, synergist muscle contraction, antagonist muscle inhibition, and adaptation of the reflex response.

They postulated that strength increases following vibration training are of hormonal modulation (ie. changes), that is essential for muscle hypertrophy and force production.

Stochastic resonance vibration 

Basically, there are two main types of vibration: sinusoidal and stochastic resonance vibration (see "vibratory platforms" above).

The sinusoidal has a constant vibration frequency, which distinguishes its "character" from stochastic resonance, which has random vibration frequencies.

Most of (if not all?) the previous studies investigating vibration and performance (jump, power, speed, sprint, agility, strength, etc.) have used the sinusoidal type vibration.
This Image shows Sine Wave-type vibration; the repetition of each vibration shows a linear combination of Sinusoidal waves in harmonic motion

This Image shows the noise and signal of Stochastic Resonance
However, the nature of the sine wave is that the stimulus is constant and therefore, predictable by the body. This is not collateral with training aims that appreciate the idea of progressive overload and variety in order to create a new stimulus required for improvement.

The fact is that humans can easily habituate (or adapted) with constant information or stimulus!

In contrast, stochastic resonance is a phenomenon in which noise is added to improve response, through vibration. The generated vibration contains random noise, which can promote unpredictable stimulus (i.e. random signal and noise), and as a result, will increase sensory sensitivity. In short, the cells are more easily excited under stochastic conditions.
Vibratory Shoe Insoles... "Stochastic resonance was delivered to the soles of the feet via controlled vibratory stimuli. Vibrations were generated by piezo-electric actuators mounted within the insoles and driven by a control unit (black box) secured to the outside top of the shoe "...Junhong Zhou et al., 2016.
The potential use of stochastic resonance training to improve athletic performance

To date, stochastic resonance is mostly used in a rehabilitation setting, such as restoration of normal functions of patients (stroke, Parkinson disease, etc.) and musculoskeletal pains - back, knee, neck, shoulder, arm, ankle, foot, and hip (see Elferig et al., 2011).

Stochastic resonance vibration has also been used to improve postural control in the older adult using 'vibratory shoe insole' (see above), apart from enhancing the perception of information essential to support motor performance, while offsetting a reduced sensory sensitivity through injury, aging and so on (see Davids et al., 2004).

Bear in mind that our body has a certain level (threshold) of detection capability and this is influenced by various factors (aging, injury etc.).

Aging people are synonymous with aging-associated diseases, illnesses, and injuries. With aging as well, sensations may be changed, which is increased weak sensory signals, which in turn, decrease detection capability.

Hence, stochastic resonance can be exploited in order to increase the detection capability (i.e. it adds up to the body's existing or present signal, that is weak due to, for example, injury/aging).

The "noise" can be mistakenly understood as the perturbation (i.e. undesirable), but the stochastic resonance should be viewed as "essential noise," see below.

In order to improve the transmission of neural signals (and detection capability), the noise must be optimal, not too high, and not too weak. If the noise is too strong for example, it cannot be discriminated against the"general noise."
Stochastic resonance is observed in added random noise (optimal/good), in contrast to high noise (detrimental)
From the above, it seems that the perception of information can be increased by the noise as a result of sensitization of the weak sensory signal (sub-threshold signal), which could have potential in sports performance settings.

If the detection capability can be amplified by an added signal to improve human function; it certainly has the potential to improve certain areas of sports performance. German scientists and athletes have been trying to utilize stochastic resonance to improve sports performance (watch SRT Zeptor Vibration Training below; SRT = stochastic resonance training/therapy).

In addition, if vibration can be used to potentiate or improve athletic performance, a combination of vibration and random noise (i.e. stochastic resonance) for athletic performance enhancement seems promising.

Further research is necessary to understand its roles for performance enhancement (e.g. jumping, strength, and speed) and in which way it can be utilized to improve training quality.

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