The purpose of this study was to investigate the effect of localised tibialis posterior muscle fatigue on foot kinematics during walking. It was hypothesised that following fatigue, subjects would demonstrate greater forefoot and rearfoot motion during walking. It was also postulated that the magnitude of the change in rearfoot motion would be associated with standing anatomical rearfoot posture.
Twenty-nine subjects underwent an exercise fatigue protocol aimed at reducing the force output of tibialis posterior. An eight camera motion analysis system was used to evaluate 3D foot kinematics during treadmill walking both pre- and post-fatigue. The anatomical rearfoot angle was measured during standing prior to the fatigue protocol using a goniometer.
Peak rearfoot eversion remained unchanged following the fatigue protocol. Although increases in rearfoot eversion excursion were observed following fatigue, these changes were of a magnitude of questionable clinical significance (<1.0°). The magnitude of the change in rearfoot eversion due to fatigue was not associated with the anatomical measurement of standing rearfoot angle. No substantial changes in forefoot kinematics were observed following the fatigue protocol.
These data indicate that reduced force output of the tibialis posterior muscle did not alter rearfoot and forefoot motion during gait. The anatomical structure of the rearfoot was not associated with the dependence of muscular activity that an individual requires to maintain normal rearfoot kinematics during gait.