A gait is a pattern of limb movements made during locomotion. Human gaits are the various ways in which humans can move, either naturally or as a result of specialized training. Human gait is defined as bipedal, biphasic forward propulsion of the center of gravity of the human body, in which there are alternate sinuous movements of different segments of the body with least expenditure of energy. Gait patterns are characterized by differences in limb-movement patterns, overall velocity, forces, kinetic and potential energy cycles, and changes in contact with the ground. Classification Human gaits are classified in various ways. Each gait can be generally categorized as either natural (one that humans use instinctively) or trained (a non-instinctive gait learned via training). Examples of the latter include hand walking and specialized gaits used in martial arts. Gaits can also be categorized according to whether the person remains in continuous contact with the ground. Foot strike One variable in gait is foot strike – how the foot contacts the ground, specifically which part of the foot first contacts the ground. forefoot strike – toe-heel: ball of foot lands first mid-foot strike – heel and ball land simultaneously heel strike – heel-toe: heel of foot lands, then plantar flexes to ball In sprinting, gait typically features a forefoot strike, but the heel does not contact the ground. Some researchers classify foot strike by the initial center of pressure; this is mostly applicable to shod running (running while wearing shoes). In this classification: a forefoot strike has the initial center of pressure in the front one-third of shoe length; a mid-foot strike is in the middle third; a rear-foot strike (heel strike) is in the rear third. Foot strike varies to some degree between strides, and between individuals. It varies significantly and notably between walking and running, and between wearing shoes (shod) and not wearing shoes (barefoot). Typically, barefoot walking features heel or mid-foot strike, while barefoot running features mid-foot or forefoot strike. Barefoot running rarely features heel strike because the impact can be painful, the human heel pad not absorbing much of the force of impact. By contrast, 75% of runners wearing modern running shoes heel strike; running shoes are characterized by a padded sole, stiff soles and arch support, and slope down from a more-padded heel to a less-padded forefoot. The cause of this change in gait in shoe running is unknown,