A quasi-static three-dimensional model of the rear foot was developed
to enable calculation of joint motion and net torque with respect to t
alocrural and subtalar joint axes. The functional behaviour of these j
oints was analysed during single-limb stance. Six female soccer player
s with unilateral functional instability of the ankle joint were exami
ned. Recordings were performed both with eyes open and eyes closed. Th
e rear-foot model was implemented into an optoelectronic motion analys
is system together with a force plate. The subtalar torque precedes th
e angular movement by 0.1-0.2 s, indicating active postural correction
s. Up to a certain limit of subtalar joint inversion, the external eve
rting torque increases. If the inversion is further increased an exter
nal inverting torque is obtained. With eyes closed the amplitudes incr
eased for joint motions, torques, centre of pressure trajectories, she
ar forces, and vertical forces. All events found with external inverti
ng torques occurred when standing on the injured foot with the eyes cl
osed.