PURPOSE: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.