Vibration G-force Impact
Impact of Vibration G-force on Human Body
In vibration therapy, our purpose is to utilize the influence of vibration acceleration as a treatment intervention. However, does the vibration acceleration also negatively impact our body?
First of all, we need to understand the vibration acceleration.
When you are on a running whole-body vibration plate, your body is subjected to the acceleration created by the vibration motion. Acceleration is created when the velocity of an object changes. In vibration motion, the velocity of the object keeps changing in reverse directions. So the vibration acceleration also keeps changing between the maximum positive value and the maximum negative value. Such a dynamic pattern makes vibration intervention unique. Let's examine the magnitude and the pattern of the vibration acceleration, and learn how it may impact our body.
Vibration acceleration is usually expressed using G-force.
For topics related to the impact of acceleration on human body, people usually use gravity G (9.8 m/s2) as the unit to express the acceleration. It is easier to comprehend the acceleration magnitude using the gravity G, because on the earth we are subjected to the gravity all the time.
The acceleration rate using the G as the unit is called G-force.
It makes more sense if an astronaut tells you that she experienced 3G at the launch of her rocket. If she tells you she experienced an acceleration rate of 29.4 m/s2, you will probably not have much idea about the magnitude.
When you stand on the ground, the earth gravity tends to pull you downward, but the ground stops the tendency.
Let's say you weigh 200LB. At 1G, there is a 1x200LB acceleration force pulling you down. Your body overcomes the 200LB gravity, and you feel your weight is 200LB.
Our body systems, organs and tissues are all used to the 1G acceleration environment in which we live on this earth.
Now you step on to a running vibration plate. At a moment, it pushes you up at an acceleration of 3G, your body will need to overcome 3x200LB=600LB downward acceleration force.
In this situation, you feel your body weight is 600LB.
In vibration motion, the upward acceleration motion only happens in the 4th phase of a vibration circle. If the vibration frequency is 30Hz, each vibration cycle takes 1/30 second. The upward acceleration is only 1/4 circle. That mean, in one vibration circle, the time period you experience 600LB is a tiny 1/120 second (0.008 second).
To summarize, if you weigh 200LB and you use a vertical movement vibration plate that vibrates at 30 Hz with the G-force of 3. In every second, you experience your body weight surging to 600LB for 30 times, each time lasts 0.008 second.
This explains the vibration impact that occurs in a vibration exercise. It is in a pattern of repeated short pulses of intensive mechanical impact.
In realty, the 600LB acceleration force is only at the bottom of your feet against the vibration plate surface. Above the feet, your flexible body absorbs some vibration, so the G-force is reduced.
Impact of High G-force
The G-force of vibration plates varies by design, but mostly fall into the range between 2G and 8G. For example, the VT007 vibration plate has the maximum G-force of 3.8.
For the comparison, a powerful fighter jet can reach an acceleration rate as high as 9G. A human payload rocket has a 3G at launch and up to 8G at re-entry.
Blood flux and blood turbulence
Vertical direction G-force on a upright human causes blood to flux from the head to the feet, or reverse direction in case of negative G-force.
Prolonged high G-force can cause blood supply problems at brain and eyes, and can cause loss of consciousness (G-LOC) or loss of vision.
For flying a high performance fighter jet, extended high G exposure can be fatal.
In vibration exercise, the high G situation only lasts for a tiny fraction of a second, then the movement direction is reversed.
This quick reverse G-force pattern only causes blood turbulence, not blood flux in one direction. It should not cause serious problem for brain blood supply.
Some people can get dizzy when vibration is transmitted to their heads. It can be either blood supply issue or nerve issue, or, a combined effect.
There are cases that people experience loss of vision when vibration is transmitted to the head. 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.
Vibration's impact on eyes has not been well studied. Negative reports on vision loss are very few.
Generally, people can get blurred vision during vibration. That is mainly because it is difficult to focus while eyes are in motion.
The other impact of high G in vibration exercise is the acceleration force's mechanical impact on our body.
Because the acceleration force takes the form of repeated short pulse and immediately released when the movement direction reversed. Our body can take this type of repeated short pulses of intensive mechanical stimulation well.
In fact, this intensive mechanical stimulation is an unique attribute of vibration therapy. Scientists consider it valuable in their exploration of utilizing this unique stimulation for health benefits.
Vibration hazards may not be exactly relevant to the discussion of G-force in this article, but it makes sense to put this information here because it is also safety related.
Extended exposure to vibration can be hazards. This mainly pertains to profession related exposure like operating tools and machinery that produce intensive vibration.
In the US, there is not a set of regulated safety standard for profession related vibration exposure. US Labor Department and National Institute for Occupational Safety and Health (NIOSH) published advisory information on hand-arm vibration exposure. NIOSH published more detailed recommendation for the standard.
Hand-arm vibration syndrome or “white fingers” is related to consecutive hours of using certain electric hand tools. This includes damage to nerves, soft tissue or joints of the hand, wrist and arm.
In other publications, researchers try to find relationship between vibration hazards and the frequency, but there have seemed no consistent results achieved.
In 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 extended exposure, but users should be aware the potential hazards of extended exposure in vibration.
In conclusion, in vibration exercise, G-force usually does not have negative impact on human body.
On the other hand, the short pulses of intensive acceleration force may create the needed mechanical stimulation for health benefits.
In regular vibration exercise, if it is not excessive, vibration is not considered as a hazard. In many clinical trials conducted to test vibration therapy's efficacy, scientists did not find prove of side effect, and their conclusion is vibration exercise is safe.
People with serious medical condition especially those with implants, should do thorough research and consult medical professionals for advise before performing vibration exercise.
- Jay Tang
Interpreting life science from a mechanical engineering perspective.