Localized ankle plantarflexor and dorsiflexor fatigue following volitional exhaustion using the Bruce protocol

BACKGROUND: There have been conflicting findings regarding the relationship between ankle muscle fatigue and a fatiguing run due to different selections of running protocol. Bruce protocol is strongly established as a maximum graded exercise test for volitional fatigue. OBJECTIVE: To determine if volitional exhaustion utilizing the Bruce protocol would result in localized ankle plantarflexor (PF) and dorsiflexor (DF) fatigue. METHODS: Twenty-three healthy individuals participated. Participants ran on a treadmill until they reached volitional exhaustion during performance of the Bruce protocol. Before and after volitional exhaustion, participants performed 3 maximum voluntary isometric contractions for both PF and DF with electromyography (EMG) assessing activation of the tibialis anterior, peroneus longus, and medial gastrocnemius muscles. RESULTS: Volitional exhaustion resulted in ankle PF fatigue (moment: [Formula: see text] 0.001), ankle DF fatigue (moment: [Formula: see text] 0.001), median frequency ([Formula: see text] 0.021) and mean amplitude ([Formula: see text] 0.001) of the tibialis anterior (TA). CONCLUSIONS: That the general fatigue induced by the Bruce protocol caused ankle PF and DF fatigue. Identifying and understanding the neuromuscular responses to volitional fatigue following running are helpful in not only improving the comfort and enjoyment of physical activities, but also in enhancing training and safety of injuries associated of these activities.