Relationship between Mechanical & Neuromuscular indices of Fatigue during Resistance Exercise: 1832 Board #93 May 31 3 30 PM - 5 00 PM

Methods for monitoring resistance exercise (RE) loads have been popularized through new technologies. However, little is known about the use of these technologies to explore the relationship between mechanical & neuromuscular indices of muscle fatigue during RE. PURPOSE: (1) To examine the relationship between changes in external mechanical variables such as Work (W), Power (P) & Velocity (V) & EMG of the quadriceps muscles during 1 set of 1-leg knee extension (RE) to failure. (2) To determine if external mechanical variables can be used as a proxy to predict EMG-based acute muscle fatigue during RE. METHODS: 28 males familiar with resistance training volunteered. Body composition (air plethysmography) & 1-RM for a 1-leg knee extension RE was completed. After at least 96 hours, subjects performed as many reps (5.4+/-1.1) as possible at 90% 1-RM until failure. EMG was collected from the vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF) of the exercise leg & VM of the non-exercise leg. Total Power (TP), Mean frequency (MF) & Area (A) spectral/amplitude data were used for EMG analysis. Mechanical data was collected via an ultrasound sensor & custom- built software to measure weight-stack movement (time & distance). 1 X 4(Reps) ANOVA & 3(Muscle) X 5(Reps) MANOVA with Repeated Measures, and a-priori contrasts were used to make specific pairwise comparisons. RESULTS: V & P for Reps1&2 (V=23.6+/-15.5 cm/s; P=182.5+/-125.4 J/s) was significantly greater than Reps3-5 (V=14.3+/-9.4 cm/s; P=107.3+/-77.8 J/s); p<0.05. W was not statistically different across Reps1-5. EMG for VM, VL & RF exhibited similar patterns of activation (no between muscle differences or interactions). TP, M & A during Reps1&2 (TP=118758+/-18066mV2/Hz; MF=254.0+/-20.7 Hz; A=571.2+/-84.5 uV/s) were significantly less than Rep3-5 (TP=229874+/-66374 mV2/Hz; MF=318.8+/-21.2 Hz; A=994.0+/-155.5 uV/s); p<0.05). CONCLUSION: Quadriceps EMG responses representative of local neuromuscular fatigue begins to occur after Rep2 during 90% of 1-RM RE. Similarly, V & P during the concentric phase of the muscles’ action significantly decrease after Rep2, without a decrease in W. These data suggest that measures of V & P can be used as proxy measures of local neuromuscular fatigue during localized high-intensity knee extension RE.