The effects of acute muscular fatigue on the functional ability of the knee joint
Brown, Tyler Nolan.
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Results of preliminary data collection indicate an increase of electromyography (EMG) amplitude in fatiguing isokinetic contractions of the knee extensors. The primary purpose of this study was to determine if the EMG/Torque relationship of vastus lateralis changes as a result of fatigue. The second purpose of this study was to determine if tests of functional ability are affected by fatigue. Twenty-two subjects (13 males and 9 females) were sampled from two populations with different types of training (strength versus endurance) experience. The procedures included a five-minute self-selected warmup on a cycle ergometer, pre-fatigue functional ability tests, fatigue protocol and postfatigue functional ability tests. The functional ability test protocol included four singleleg hopping drills to assess the functional performance of the knee joint. Torque was measured on an isokinetic dynamometer at 60 degrees per second through a functional range of motion until acute fatigue was reached during the fatigue protocol. Surface EMG electrodes were placed over the vastus lateralis to develop an EMG/Torque ratio during the dynamic contractions. The results indicate training type did not significantly affect torque production (p = 0.373) or the EMG/Torque ratio (p = 0.744) during isokinetic knee extensions in response to acute muscular fatigue. The strength-trained sample tended to have a greater increase of the EMG/Torque ratio during the fatigue protocol. The results did indicate that there were two significantly different types of response to acute muscular fatigue (p < 0.001). There were significant differences between the preand post-fatigue functional ability tests for the M/L (p < 0.001) and Up/Down (p = 0.011) but not for 3-Forward (p = 0.408) or Figure-8 (p = 0.286). One group doubled their activation magnitude during the fatigue protocol, while another group did not increase their activation magnitude during the fatigue protocol. It is possible that the increase of activation magnitude seen during the fatigue protocol is a result of transition of fiber type utilization. Further study is needed to determine what is the primary cause of the muscleαs response to acute muscular fatigue.