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Comparison of EMG Muscle Activity and Turn Times Using Orthosis and Stock Insoles During Skiing: 199 Board #40 May 30 9

PURPOSE: Anchoring exercise intensity with ratings of perceived exertion (RPE) can be used to examine the mechanisms underlying the perception of effort during fatiguing tasks. The purpose of the present study was to examine the fatigue-related patterns of responses for force and electromyographic amplitude (EMG AMP) during sustained isometric, leg extension muscle actions anchored by RPE. METHODS: Ten recreationally active men (mean ± SD: 22.9 ± 2.7 yr) performed 3 randomly ordered, sustained submaximal isometric leg extension muscle actions (knee joint = 120°) anchored at RPE values of 2, 5, and 8 (OMNI-RES 10-point scale) to volitional exhaustion or a maximal time limit of 5-min. Maximal voluntary isometric contractions (MVIC) were performed prior to and immediately following each sustained isometric muscle action and bipolar surface EMG signals were recorded from the vastus lateralis muscle during the sustained muscle actions. Linear regression analyses were used to examine the force and EMG AMP vs. time relationships during each sustained isometric muscle action. RESULTS: The pretest MVIC values (62.1 ± 14.4, 62.6 ± 14.7, and 63.5 ± 12.7 kg) were highly reliable (ICC= 0.90) and were not significantly (p=0.930) different. The posttest MVICs were significantly (p<0.001) less than pretest for each sustained isometric muscle action. There were significant (p<0.001) differences between all the mean times for the sustained muscle actions (RPE 2 = 300.0 ± 0.0 s; RPE 5 = 202.0 ± 95.5 s; RPE 8 = 72.7 ± 27.6 s). Furthermore, the percent decline in force decreased (p<0.001) with each increase in RPE (percent decline for RPE 2 = 61.0 ± 18.5%; RPE 5 = 47.4 ± 19.6%; RPE 8 = 24.9 ± 13.2%). For normalized EMG AMP, there were significant negative, linear relationships for RPE=2 (p=0.006) and RPE=5 (p=0.003) vs. time of the sustained isometric leg extension. CONCLUSION: For the RPE=2 and RPE=5 trials, EMG AMP and force decreased and, therefore, were dissociated from RPE. At RPE=8, however, EMG AMP was unchanged, but force decreased. Thus, EMG AMP tracked RPE, but was dissociated from force. Together, these findings suggested that the perception of effort during sustained, submaximal isometric leg extension muscle actions were not mediated by fatigue-related changes in force or EMG AMP.