One stride (heel strike to heel strike of one leg) of normal gait has been divided into the stance (62%) and swing (38%) phases. The stance phase is further divided into heel strike, foot flat, and toe off. Proper gait requires coordinated contraction of the leg muscles. The tibialis anterior (TA) muscle fires eccentrically at heel strike to lower the foot to the ground, while the gasto-soleus (GS) complex is dormant. The TA then relaxes, while the GS eccentrically contracts as the body’s weight is transferred forward over the foot during foot-flat. As the foot propels the body forward during toe-off, the GS contracts concentrically, while the TA remains dormant. As swing commences, the TA then fires concentrically producing dorsiflexion to clear the foot over the ground while the GS relaxes. Certain conditions like cerebral palsy result in improper firing of the muscles during the gait cycle, resulting in altered gait mechanics.
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