This page provides a technical overview of how to calculate the force a vaulter experiences during a fall, including an introduction to g-force calculations with references and sources, an official test method that uses readily available tools, comparisons to other sports, and finally, recommendations specific to vaulting.
Formulas taken from Brauer, Roger L. "11-2: Falls" Safety and Health for Engineers. 2nd ed. Hoboken, NJ: John Wiley, 2006. 142-43. Print.
Velocity Upon Impact (v)
Rate of Deceleration (a)
When combining the above formulas we can reduce / cancel out all the way to just:
Both Height and StopDist must be in the same units of measurement, so if using a Height of Meters and a StopDist of Centimeters, the final formula is:
Test Metric for these formulas provided by www.HazardControl.com :
From example on Page 7 of http://www.hazardcontrol.com/factsheets/pdfs/falling-objects-calculations.pdf
This test method will only work with sand, or mostly sand based footing. It may or may not be feasible to develop affordable and simple test methods for other footing materials in the future.
To calculate the Height input, measure the distance from the ground to the highest potential a given vaulter / horse combination could attain for the vaulter's center-of-gravity with the potential skills being performed.
To calculate the StopDist input, use a 4.5 kg metal kettle bell weight (not the larger sand filled type.) Such kettle bell weights are readily available at any store that sells consumer weights for home use. Drop the kettle bell weight from the input Height. Measure the impact dent with two rulers: one ruler only to span the dent as a marker and the other ruler to measure the depth of the dent. The depth of the dent should be used as the StopDist input. In very deep sand it may not be possible to pull the kettle bell weight out of the sand without the hole it created filling in again. In such a case carefully rotate the ball to vertical and then mark the kettle bell weight at the sand line before lifting it out of the sand; then measure the height of the mark from the base of the kettle bell.
As a point of reference, research published by the Journal of Athletic Training has ascertained that the "approximation of fall height bellow which a life-threatening head impact injury would not be expected to occur" onto a traditional wood gym floor is 1.4 m, not much higher than that of a mature athlete's center-of-balance to begin with. Although straight-drop falls in most gym sports are not the norm, they clearly do not cause grave concern. Given an estimated absorption of such a floor of no more than 0.5 cm (probably less) we can compare the output of this guideline of 280g (or more) to other measurements.
A long-time member of the ASTM's equestrian protective-headgear committee is quoted that "The threshold at which the most serious head injuries occur is 300g, so all helmets must be under that -- and not even the tiniest bit over." http://www.equisearch.com/tack_apparel/english-tack_apparel/safety100703/
However, the NHTSA standard (automotive) for a sudden impact acceleration on a human that would cause severe injury or death is 75g's for a "50th percentile male", 65g's for a "50th percentile female", and 50g's for a "50th percentile child". These figures assume worst case scenario for taking the impact on the chest/stomach, the back, side, or the head.
A note for the reader to consider: The reason severe injuries due to head impact are not more common in gym sports, despite the potential for very high g-forces is that the participant’s reflexes from lifelong experience protect the head from hitting the ground with the full potential force. Because these reflexes don’t naturally transfer to falls from higher heights, learning and practicing vaulting “bailout” rolls is critical for reducing the exposure a vaulter has to full-force falls.
Any vaulter who experiences an uncontrolled fall without a clean roll that keeps the head off the ground should always be assessed for concussions. Look for the Concussion heading on the Resources page of http://parachutecanada.org . If there is any suspicion of a concussion the vaulter must not continue with physical activities and seek medical assessment; it requires very little force to sustain compounded concussions with more severe symptoms.
Vaulting must be conducted a safe distance from walls and other vertical objects; a minimum of 2.5 meters with a consistent circle, and preferably more. Other than mats and safe vaulting barrel(s), the arena should be free of objects that participants would be injured by if fallen on.
"Bailout" training of vaulters to develop protective roll reflexes must be to a level that corresponds with the level of risk that vaulter will experience from the skill selection being trained.
Helmets should not be used for vaulting, due to the straps of a helmet being designed and tested to not stretch or break, they then become a hanging hazard in a vaulting environment for all but the most basic positions, or when multiple people are on the horse. Helmets with break-away straps (if such a thing existed) are not workable due to a dislodged helmet from an otherwise minor fall could cause a sever neck injury. No helmet manufacturer today makes a helmet that is designed or certified for vaulting. However, all persons riding a horse, instead of vaulting, must wear a helmet since riding occurs near walls and other hard objects, and not on a consistent circle. In any vaulting situation were abnormal hazards exist a helmet must also be used, but with the vaulting then limited to only the most basic skills (head must not be near any tack) and never with multiple people on the horse.
These calculations and the methods presented here are not to be considered perfect; they are approximations due to unknowns and reasonable assumptions. The variables and factors they ignore are not expected to adversely affect the final outcome of the tests to determine the suitability of the footing. The purpose of these calculations, methods, and guidelines are not to guarantee that a life threatening injury is impossible, but instead to be in line with expectations from other sports and life activities. Without these, we would be blindly accepting an unknown level of risk.