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

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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How to Improve Sprint Performance Using Strength Training?

Strength is a fitness component that crucial for sports requiring high-speed and short term effort. This includes sprinting on the track (athletics) and on the field (rugby, soccer, etc.)

Greater muscular strength can improve the ability to produce power and rate of force development (RFD), which are prerequisites for enhancing sprint performance.

Power and RFD are the qualities that clearly separate between sprinters of different sprinting ability levels.

Interestingly, a recent review also suggests that having a sufficient strength level may also helpful for injury prevention.

Furthermore, one must consider an appropriate strength development in order to maximize its transfer into sports performance. Good programming is, therefore, necessary (this requires another thread of discussion!).

Regardless of training strategies (periodization), the force-velocity curve must be understood, which is the relationship between velocity and force that can determine the selection of load intensity and exercise. Thus, several strength qualities need to be considered by a coach when developing a sprinter, as follows:

a) Basic strength
Associated with an increased ability to produce force. Basic strength can be developed all year round although some weeks (microcycle) or months (mesocycles) may not the number one priority.
Examples of basic strength development for sprinters as follows:

Reps: 5-8 reps
Sets: 3-4 sets
Percent: 85-90%
tempo: Fast contraction
Exercises: Power clean, back squat, bench press

b) Maximal strength
Similar to basic strength, performed as the progress of basic strength. The goal of maximal strength training is to improve the ability of muscles to produce high force production, which is necessary to improve high-level power and RFD. The key when performing maximal strength is executing "high contraction velocity" (felt like as performing fast movement) during the lifting, against a very high external load.

Reps: 2-4 reps
Sets: 4-6 sets
Percent: 90-95%
Tempo: Fast contraction
Exercises: Power clean, half squat, bench press

c) Strength-speed
The goal in strength-speed exercise is to perform the exercise as fast as possible, against a heavy load. This should be utilized after completing a phase when maximal strength was the focus.

Reps: 5-6
Sets: 3-4
Percent: 70-80%
Tempo: Fast contraction
Exercises: Power clean, half squat, bench press

d) Speed-strength / explosive strength
The goal in speed-strength exercise is to perform the exercise as fast as possible, against a lighter load. The key when performing speed-strength is "vigorous extension" of joints (or extremely fast action). This strength quality must be considered in order to develop a powerful athlete (sprinter).

Reps: 6-8
Sets: 3-5
Percent: 20-30%
Tempo: Fast contraction
Exercises: Countermovement clean, jump squats, hang snatch, arm swing with a light load

e) Reactive strength
This is another priority when developing a sprinter. Reactive strength is the ability to change quickly from eccentric to concentric, or stretch-shortening cycle. Having a good reactive strength is associated with the ability to produce high force within a short period. In sprinting, the higher force one develops within 100 milliseconds (typical ground contact during late acceleration, as an example) the better (faster) the athlete. Hence, improving reactive strength can enhance rebound performance or fast ground contact - and sprint performance.

Reps: 6-10 
Sets: 3-4
Percent: Bodyweight or with very lightweight
Tempo: Fast contact on the ground
Exercises: drop jump, bounding

Read more about explosive and reactive strength here.

Meanwhile, specific strength development (e.g. sled pulling, hill run, etc.) must also be considered in order to maximize the transfer of strength into functional power, which are crucial for sports performance. However, this is another topic that requires another post.

One commonly asked question in strength development is related to how much load one must lift in order to be deemed sufficient, particularly for sprinting.

A quick answer is "depend on sports". Broadly speaking, one who has a relative strength value of 2.00 in the back squat is considered "strong" and able to take advantage of optimized the potentiation effect.

In layman, stronger athletes can be more powerful and sprint faster.

Meanwhile, exercise selection can be determined by understanding the segment of force-velocity interaction. Some exercise is high-velocity in nature and some others can be customized to be high-velocity or force based on training goals, or desired adaptations.

a) High-velocity exercise (low load) - jump squat, drop jump, power hurdling, assistance (band) training

b) High-force exercise (high load) - deadlift, back squat, power clean, overhead press

c) High-velocity or high-force exercise (customizable) - power clean, power clean, snatch, overhead press

Practically speaking, one can enhance power production by improving either force or velocity, or both.

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