Joint Angle And Anchoring Scheme Affects Performance Fatigability And Electromyographic Responses Following Fatiguing Isometric Tasks

PURPOSE: The purpose of this study was to examine the effects of joint angle and anchoring scheme on MVIC and electromyographic (EMG) responses at task failure following sustained, isometric forearm flexion tasks in women. METHODS: Ten women (age: 21.0 ± 2.8 yrs; height: 168.5 ± 7.2 cm; body mass: 68.0 ± 7.2 kg) performed 2, 3 s MVICs at joint angles (JA) of 75°, 100°, and 125° (randomized) before and after sustained, fatiguing isometric forearm flexion tasks to failure at joint angles (FJA) of 75° and 125° (dominant arm), anchored to a rating of perceived exertion (RPE) of 8 (RPE = 8) and the initial torque that corresponded to RPE = 8 (TRQ), while EMG signals were recorded from the biceps brachii. For the RPE = 8 visits, task failure was defined as RPE > 8 or torque reduced to zero. For the TRQ visits, task failure was defined as the inability to maintain the target torque. Separate 2 (Anchoring Scheme: RPE = 8 and TRQ) x 2 (Fatiguing Joint Angle: 75° and 125°) x 3 (MVIC Joint Angle: 75°, 100°, and 125°) repeated measures ANOVAs were performed for percent changes in MVIC, EMG amplitude (AMP), and EMG mean power frequency (MPF). RESULTS: The pre-test MVIC at JA100 was significantly greater than both JA75 (p = 0.001) and JA125 (p = 0.002). There was no significant (p = 0.369) mean difference in time to task failure (TTF) for FJA75 (73.9 ± 38.4 s) versus FJA125 (80.8 ± 76.5 s) when anchored to TRQ, but when anchored to RPE = 8, FJA75 (361.7 ± 260.0 s) was significantly greater (p = 0.009) than FJA125 (152.3 ± 90.4 s). For the percent change in MVIC, MVIC JA125 (23.7%) was significantly greater (p < 0.001) than MVIC JA75 (15.3%), but not MVIC JA100 (19.6%, p = 0.038). During the fatiguing tasks at FJA75, EMG AMP decreased for MVIC JA100 (16.7%) and MVIC JA125 (16.3%), but MVIC JA100 had a significantly greater (16.7%, p = 0.004) percent change than MVIC JA75 (-1.5%). For EMG MPF, there were decreases for both anchoring schemes, but TRQ had a significantly greater (11.5%, p = 0.003) percent change than RPE = 8 (2.7%). CONCLUSIONS: Following the fatiguing tasks at FJA75 (RPE = 8 and TRQ), the decreases in EMG AMP and MVIC at MVIC JA100 and MVIC JA125 suggested that both central and peripheral fatigue contributed to the decline in MVIC. For MVIC JA75, however, the decline in MVIC, but increase in EMG AMP were likely due to peripheral fatigue.