vibration G-force impact on Human Body

How Vibration G-force Physically Affects Human Body

To properly use vibration plate for health improvement, we need to understand its intensity, movement pattern and how it affects our body.

Vibration plate pushes our body to move with acceleration. This pushing force is the mechanical stimulation that we are interested in. We can learn the attributes of this pushing force through learning the acceleration.

According to Newton’s second law, the pushing force is calculated with the equation F = ma.

m: the mass of our body
a: the acceleration of the platform movement

We know the mass of our body is our weight (when on earth). Acceleration is the factor that decides the attribute of the pushing force.

G-force is usually used to express acceleration when it comes to the topic about the acceleration's influence on human body.

Then F = ma can be interpreted as

Pushing Force = Body Mass x G-force

G-force (acceleration) represents the magnitude of the pushing force on our body. It indicates the intensity of a vibration plate, and is used to compare different vibration plates.

G-force of vibration motion has unique characteristics that makes vibration stimulation special. In this article, we will examine vibration G-force about its characteristics and its physical influence on our body.

in this article
  • G-force & Pushing Force
  • Vibration G-force has unique characteristics
  • How G-force physically affects the human body
    • Blood flux and turbulence
    • Mechanical impact
    • Skeletal muscle contraction
  • Vibration hazards
  • G-force range of various vibration plates

G-force & Pushing Force

G-force is acceleration that uses the acceleration of gravity(G) as the unit. It is not a force, but an acceleration, or an acceleration ratio to be exact.

gravity G

The reason of using G as the unit is because we can easily perceive and comprehend the acceleration with the reference of the acceleration of gravity which we experience all day long when on earth.

When we stay put on the earth ground, we are subject to 1G acceleration, 1G=9.8m/s2.

We can say an astronaut is subjected to 3G (3 times of the acceleration of gravity) during his rocket launch, instead of saying that the astronaut is subject to 29.4m/s2 acceleration, which is a little difficult to comprehend its magnitude.

Beoing 747 Take-Off

Let's get a better sense of G-force through riding an airplane.

A Beoing 747 airplane needs to achieve a speed of about 160 knots to take off. On the runway, it takes about 30 seconds for the airplane to get to this speed. The acceleration of the take-off period is about 0.28G.

G-force = 160x1.85x1000/3600/30/9.8 = 0.28

Since G-force is an acceleration, how it is translated to the pushing force that we want to learn.

As we talked a little earlier:

Pushing Force = Body Mass x G‑force

Let's use an example to explain how easy it is to convert G-force to force.

bone tissue

Say you are a 200Lb payload on a rocket. During the launch, you are subject to 3G acceleration. You will get a pulling-down force of 200Lb x 3 = 600Lb. You feel as if your body weighs 600Lb.

Using G as the unit makes the calculation easy.

Please note that the G-force for rocket launch is usually defined as the G-force that astronauts are subject to, which includes the acceleration of gravity (1G). In this example, the actual G-force of the rocket created from the velocity change during the launch is 2G. The impact on the payload becomes 3G after adding the acceleration of gravity. For rocket launch, the acceleration of gravity (1G) can be simply added to the G-force of the rocket, because both acceleration vectors are on vertical direction.

For a vibration plate, acceleration of gravity should not be included in its G-force calculation, but when it comes to the calculation of the G-force on the user, acceleration of gravity needs to be included. On the vertical direction, we can simply add 1G.

Inside the Beoing 747

Back to your experience in riding the Beoing 747.

During the take-off, you get a 0.28G forward acceleration. Let's say your chest weighs 50Lb. You get a 50Lb x 0.28 = 14Lb force pulling your chest to the seatback.

In this case, the acceleration of gravity is not added. At the take-off, the airplane creates horizontal G-force. The acceleration of gravity is on the vertical direction. The gravity does not add to the force that pulls you to the seatback.

Now that we have learned about the G-force and how to calculate the pushing force it created, it will be easy for us to look at the G-force of vibration and how it behave differently.

What we want to get from using a vibration plate is the vertical upward G-force, which creates a pull‑down force on our body.

In this article, we only examine the vertical upward G-force.

Vibration G-force has unique characteristics

In the above rocket-ride example, your body is subject to a sustained 3G acceleration during the rocket launch. You get a sustained 600Lb push-up force for several minutes.

On a vibration plate, however, it has a different scenario. The G‑force of vibration motion is not a sustained value. As vibration plate moves up and down, its G‑force fluctuates between the max positive value and the max negative value in each movement cycle which lasts only a fraction of a second.

The G‑force defined for vibration plate is the G-force of the 4th phase of a vibration cycle, when the vibration plate accelerates upwards. It lasts only 1/4 of a vibration cycle.

example: ride a vibration plate

Now, assume that you ride a vertical vibration plate running at 30Hz frequency with 2G acceleration. Your body mass is 200Lb.

When vibrated, your body moves up and down 30 cycles per second.  In each cycle, only for 1/4 of the cycle your body is accelerated upwards.  That means you are pushed up with acceleration for 1/120 second (0.008 second) in each vibration cycle.

Therefore, in each vibration cycle, you get a push up force of 400Lb (200Lb x 2) for 0.008 second. Adding your body weight, your body takes 600Lb pull-down counter force.

0.008 second is so short a period that you don’t even perceive you ever experience the 600Lb force, but you do get this magnitude of mechanical stimulation 30 times per second, each occurrence lasting 0.008 second.

Vibration G-force creates a dynamic force pattern - rapidly repeated short pulses of pull‑down force on your body.

As you can see that vibration G-force is in a rapidly repeated short pulse pattern. It can put a big pull‑down force on your body, but you don’t perceive that magnitude because of its short pulse pattern.

Vibration plates can provide high magnitude mechanical stimulation pulses to your body without stressing your musculoskeletal system.

How G-force physically affects the human body

In term of the impact on human body, the short pulse pattern vibration G-force is different from the sustained G‑force. We can get a better understanding by comparing the impacts from these two forms of acceleration.

Blood flux and blood turbulence

When you are upright and subject to a vertical upwards G-force, you will experience blood flux from your head to feet, causing blood supply issue at your head.

Sustained upwards G-force can cause sustained blood supply problems at brain and eyes, and can even cause loss of consciousness (G‑LOC) or loss of vision.

g-force of fighter jet

Extended high G-force exposure, like from performing a fighter jet stunt, can be fatal for people that is not properly trained.

On a vibration plate, the upwards G-force only lasts for a tiny fraction of a second, then the movement direction is reversed.

This quickly reversed G-force does not cause blood to flux in one direction. Rather it causes blood turbulence, which does not cause brain blood supply issue.

Some people may get dizziness when their their heads are vibrated. This usually is not because of brain blood supply issue, but a natural reflex related to the sense on abnormal hearing and sight due to vibration motion, like in motion sickness.

Vibration's influence on eyes has not been studied, but negative feedbacks are rare.

People can get blurred vision during vibration, because it is difficult to focus while eyes are in motion. Just like you can not read when you ride a bumpy car. Once vibration stops, the vision resumes.

Eye retina is very sensitive to low blood pressure. Insufficient blood supply can cause the retina not to function properly. Prolonged insufficient blood supply can cause permanent damage to retina.

Without knowing the potential impact of vibration on your brain and eyes, you should adjust your exercise pose to avoid vibration from being transmitted to your head.

Mechanical impact

Another influence of upwards G-force is the pull‑down force on our body.

On a vibration plate, as vibration force pushes you up, your body feel a pull-down counter force. The force has a repeated short pulse pattern. It is immediately released when the acceleration direction reversed. In such a pattern, our body does not perceive high mechanical impact even on a high G‑force.

If you stand straight on the vibration plate, your knee joints are subject to repetitive mechanical impact. It is unclear if the repeated short pulses of high magnitude impact can harm your knee cartilage. You should keep your knees bent (squat pose) so that your flexible knee joints and muscles can absorb and resist the pull‑down force, reducing the mechanical impact on the cartilage.

In fact, squat exercise on a vibration plate creates less mechanical impact on your knee cartilage than jogging does, because your knees always keep in bending posture on the vibration plate.

Squat is also the right pose to allow vibration to induce skeletal muscle contraction around your knees and hips, which can effectively exercise your muscles, tendons, ligaments, bones and nerves.

Skeletal muscle contraction

Vibration G-force induces rapidly repeated skeletal muscle contraction due to our instinct muscle stretch reflex response.

This influence is unique to vibration stimulation. Skeletal muscle contraction is usually voluntary, commanded by the brain. Vibration-induced skeletal muscle contraction, on the other hand, is involuntary. It responds to vibration frequency in a rapidly repeated pattern.

The rapidly repeated muscle contraction effectively activates and exercises muscles and the connecting tissues. The contraction force is the needed mechanical stimulation that promotes cell regeneration for muscles, tendons, ligaments, bones and nerves.

Skeletal muscle contraction also improve circulation of blood and lymph due to the skeletal muscle pump effect. The dynamic muscle contraction induced by vibration makes the skeletal muscle pump more effective and efficient.

The rapidly repeated skeletal muscle contraction is the core treatment intervention of vibration therapy.

Vibration hazards

Vibration hazards may also relate to vibration G-force.

vibration hazards

Prolonged exposure to vibration can be hazardous. Vibration hazards mainly pertain to occupation related exposure like operating power tools and machineries that produce intensive vibration.

Hand-arm vibration syndrome is probably the one significant concern that US Labor Department and NIOSH published advisory information for vibration exposure. 

Hand-arm vibration syndrome or “white fingers” is related to consecutive hours of using certain electric hand tools. The syndrome includes damage to nerves, soft tissue or joints of the hand, wrist and arm. The mechanism of the cause is unclear.

In the US, there is not a set of regulated safety standard for occupation related vibration exposure.

In other publications, researchers try to find relationship between vibration hazards and the frequency, but there have not been any consistent results.

For vibration exercise, the use of vibration plate is usually less than 20 minutes a time, one or two times a day. This  is not considered as a prolonged exposure. Anyway, users should be aware about the potential hazards of prolonged exposure of vibration and not to use vibration plate excessively.

In the limited clinical trials conducted to test the efficacy of various vibration therapy applications, scientists did not observe any health hazard from using vibration plates.

However, improper use of vibration plate, like improper use of any other exercise equipment, may cause injury. The rapidly repeated G‑force can amplify the negative effects.

People with serious medical condition should do thorough research and seek professional advice for using vibration plate.

People with hip or knee replacement should not use vibration plates. The rapidly repeated mechanical impact from vibration may loosen the bond between the implant and the underlying bone. There is no scientific study in this regard, but it is right to take a risk‑averse strategy until we have better understanding of the influence.

G-force range of various vibration plates

G-force is an important indictor of vibration intensity for comparing various vibration plates.

If the product information does not include G-force, you can get the frequency and the amplitude to calculate the G-force using the formula below:

Vibration G-force = 8πf2A/9.81

vibration G-force formula

In this article, we only discuss the vertical direction G-force.

For most vibration plate models in the market, their vertical G-force are in the range from 0.1G to 4G.

Almost all pivotal oscillation type of vibration plates are designed with adjustable frequency, so their G-force are adjustable, usually in the range from 0.1G to 2.5G.

Some linear vibration plates are designed with fixed frequency and fixed amplitude, so they offer a narrow range G-force. For linear vibration plate, the amplitude yields to the body weight, so is the G-force.

Some other linear vibration plate are designed with adjustable frequency and amplitude, so they offer a wide range G-force. For example, VT007 and VT003F has an adjustable frequency from 15Hz to 40Hz and two amplitude settings. They offer G-force range from 0.1G to 3G.

Galileo models, the German made pivotal oscillation type of vibration plate, can achieve G-force up to 10G. Galileo machines are extremely high intensity models.

Marodyne and Juvant models work at very low G-force, about 0.1-0.2G. These two are extremely low intensity models.

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