Thursday, June 12, 2008
Foot mechanics in sport
In the domain of nonsense and sports prowess predictions, it is widely believed if the great toe is longer than the second toe (often the longest) then you will become a champion skier or sprinter. Absolutely no evidence to support this premise but it may have some scientific substance, nonetheless. The great toe is the end of the most important pivot of the foot and together with the ankle, gives a superb mechanical advantage to propel the weight bearing foot through space, which takes care of sprinting. A sound first metatarsophalangeal joint also offers lateral stability to the foot, which would be critical in skiing. The key to the foot's secret is the ability to lock and unlock the forefoot against the rear foot. Simply moving the heel from side to side does this. External turning of the heel (pronation) unlocks the forefoot and causes the extremity to become a mobile adaptor. This is useful when contacting the ground. Internal rotation of the heel (supination) causes the foot to lock giving a rigid lever to propel the foot forward. The stance phase of gait comprises of a complex unlocking and locking of the forefoot against the rear foot most of which is determined by turns and twist from above the foot and ground reaction forces. Feet form the foundation of most sports, whether acting as hydrodynamic rudders in swimming, stable pedestals in archery or shooting, springs and levers that propel track and field athletes, jinkers and weavers in soccer and hockey or mobile adaptors in cycling. In basketball and handball the feet are launching pads for leaps and landings and in tennis and gymnastics they act as brakes, balances and pivots for side to side motions. In Taekwondo, feet are formidable weapons whereas in rowing and equestrian sports they act as grippers and levers. The unique structure and function of feet simultaneously support body mass, balance and propel the body whilst absorbing shock during locomotion. The real success of feet is in their arch construction. We are more familiar with the medial arch but there is also one on the outside of the foot, and an anterior arch, across the ball of the foot. Some experts say this transverse arch is a morbid arch and only becomes apparent after we die but together they give feet a unique advantage over all other living creatures. William Rossi reported the intersection of the arches during locomotion corresponded precisely to the area of the calcaneo-cuboid joint on the lateral column of the foot. The significance of which is the foundation for bipedal locomotion. Biomechanists and anthropologists agree this is the critical difference between the feet of hominids and other primates and gives humans the ability to bear weight on both feet. Feet respond constantly to changes in the strength and direction of downward forces as we move as well as the upward reactions from ground contact. The medial arch stores energy during full foot contact before releasing it as the heel lifts off the ground. Mobility of their joints helps many athletes but an unstable foot or flat foot might give considerable leverage to a long distance runner. Repetitive activities require unusual muscle strength but provided the feet are protected in appropriate footwear, and the athlete toned to perfection, then stress related injuries are minimized. Sprinters and jumpers need rigidity and may be further advantaged by equinus feet (horse like) with the forefoot sitting lower than the heel. In this way the physical make up of an athlete determines the kind of sport they have a natural aptitude for. Field sports like soccer, and tennis with short runs, constant changes in direction, turns and twists prefer mobile feet, which form stable, contact with the ground. Gymnasts prefer feet that are both tactile and mobile adaptors. Competition shoes should not impede the natural ability of feet to locomote and hence the emphasis on comfort. The function of sports shoes has much to do with protecting the body from trauma and pathological compensations brought about by persistent and extreme activities.