This is an interesting enquiry. The response can be illustrated by the following comparison. A six-foot tall man who was a student of mine fell and broke his forearm. A woman about 5’6″ fell and broke her forearm. One slipped forward and tried to break the fall with the left arm. The other fell backwards and tried to break the fall with her left arm. Both had no training on how to fall.
Both slipped and fell. That would indicate that bones can break on impact from slipping from above knee height, or about 3 1/2 feet. A body falling flat on impact could suffer broken bones from shoulder height. This can be surmised by observing the FIFA women’s games. A normal shoulder height would be 5 feet.
A rib bone, a leg bone, a shoulder bone or the spinal cord might possibly break in a flat fall from shoulder height or from 5 feet. According to at least one report, a passenger who jumped from the wing of a crashed airplane broke a bone. The height of the wing to the ground was reported at 14 feet. There have also been reports of passengers sliding down an emergency chute and breaking a bone. The end of an emergency chute would be about 3 feet off the ground. An older person rolling off a bed might break a bone. A normal height of a bed frame on wheels, box spring and mattress would be about 2 1/2 feet to 3 feet. A wheelchair bound person falling forward could break a bone on impact. That would be from about knee height at 1 1/2 feet to about shoulder height at 4 1/2 feet. A person falling from the first step of a ladder may also break an arm bone if he or she tried to break the fall with the arm. That would be from 4 feet.
Whether bones break also depends on the surface on impact. Concrete, cement, pavement would most likely result in broken bones but a bean bag, a canopy, a trampoline would not likely result in broken bones unless the acrobat falls off the trampoline onto a hard surface. A trampoline is usually 4 to 5 feet off the ground depending on how taut it is. Children’s trampolines may only be 1 foot to 2 feet off the ground.
In the Puma (Mexico) and FC Dallas soccer game (August 17, 2011), Puma player Sandoval was in the air on top of the shoulders and the back of the head and neck of an FC Dallas player. The Puma player was in the air in a horizontal position facing the sky. He fell onto the turf on his buttocks with his torso at about 30 degrees to the ground. As soon as he hit the ground, he rolled sideways and rested face down with arms and legs extended straight. This is a good illustration of a good fall from shoulder and neck height, a minimum of 5 feet in the air. Soccer players are generally quite tall at an average of 5’11” to 6’1″. So the Puma player’s fall was from at least 5 feet in the air.