Alteration of the position sense at the ankle induced by muscular fatigue in humans

The purpose of this study was to investigate how an isometric exhaustion test affects the position sense at the ankle using an active matching task. Eight male subjects with a mean age 24.6 yr participated in the study. Subjects' ability to match the right ankle with the position of the left reference ankle position-determined using signed and absolute errors and variability-was investigated. This task was realized for four ankle angular values (in degrees), two in dorsiflexion (P(-20), P(-10)) and two in plantarflexion (P(20), P(10)) and for two experimental conditions: 1) normal and 2) fatigue. Muscular fatigue was induced in tibialis anterior (TA) of the right leg (ankle dorsiflexor) by using an isometric test. Subjects were instructed to maintain a workload of 70% of their maximal voluntary contraction in series of 40 s. With fatigue, subjects produced ankle movements characterized by greater absolute errors for movements of large amplitude in dorsiflexion and for movements of small amplitude in plantarflexion. In addition, using a "worst-case scenario" analysis, results showed that errors were significantly greater than the normal functioning range for 20 degrees dorsiflexion and 10 degrees plantarflexion positioning. The acuity of the position sense at the ankle is reduced subsequent to a fatigue protocol. The influence and the potential deleterious effects of muscular fatigue on position sense are discussed.