DIFFERENT STRATEGIES TO COMPENSATE FOR THE EFFECTS OF FATIGUE REVEALED BY NEUROMUSCULAR ADAPTATION PROCESSES IN HUMANS

An initially submaximal hopping task was maintained with the same glob al power output until it became the maximal performance; since there w as no decrease in performance, any change in behavior occurring with f atigue characterizes the strategies allowing to compensate for the eff ects of fatigue. In a prolonged hopping task, fatigue is likely to be most prominent in the ankle extensor muscles since they are the main c ontributors to vertical propulsion in the hop. With fatigue, all subje cts landed with more flexed knees and with an increased activity in th e biarticular rectus femoris muscle indicating some compensation betwe en the knee and ankle joint. Furthermore, two different strategies app eared to further compensate for the important fatigue of the ankle ext ensor muscles: one was organized across joints and consisted in a heav ier reliance of the knee extensor vastus lateralis, and the other was organized within the fatigued joint and consisted in an earlier preact ivation of the gastrocnemius. As a consequence, two different adaptati ons of the ground reaction force profiles appeared at the end of the s ession; each being related to one of these two strategies.