Recruitment Patterns of The Adductor Muscles During Incremental Fatiguing Pedaling

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PURPOSE: It has been reported that the adductor magnus (AM) muscle, a member of the adductor (AD) muscle group, showed higher activation and the degree of activation of this muscle was correlated with power output during sprint pedaling based on muscle functional magnetic resonance imaging (mfMRI) finding. However, it isn't well understood, so far, how this muscle acts in pedaling. Therefore, the purpose of this study was to investigate detailed activation patterns in the AD muscle group, i.e. the AM and adductor longus (AL) muscles, during incremental fatiguing pedaling using surface electromyography (EMG). METHODS: Seventeen healthy men performed incremental pedaling on a bicycle ergometer until exhaustion. The workload increased by 30 W every 2 min starting from 60 W at 60 rpm of cadence. The surface EMG was recorded from the AM, AL and vastus lateralis (VL) muscles. The electrode location of the AM and AL muscles was identified by ultrasonography. Exhaustion time (ET) was divided into ten stages; the root mean square (RMS) of raw EMG activity was calculated for each stage. All EMG activity data was expressed as the relative value to that of the first stage, i.e. RMS at 10%ET was the baseline. To analyze crank phase dependent activation patterns, one crank cycle was divided into the extension and flexion phases based on the hip and knee joints angle, EMG activity of the AD muscles was measured each phase. RESULTS: The ET and power output at exhaustion was 10.9 ± 1.9 min and 209.1 ± 35.7 W, respectively. EMG activity of the AM, AL and VL muscles significantly (p<0.05) increased after 50%ET, 70%ET and 30%ET, respectively. At 100%ET, there was no significant difference in EMG activity between the AM (1.9 ± 0.6) and VL (2.2 ± 0.7) muscles; however, that of the AL muscle (1.6 ± 0.6) was significantly lower than that of the VL muscle. In analysis of crank phase dependent activation, EMG activity of the AM muscle during extension phase significantly increased after 70%ET compared with flexion phase (p<0.05). CONCLUSIONS: These results suggested that the level of activation in the AM muscle did not differ to the VL muscle during incremental fatiguing pedaling and that the AM muscle would contribute to power output of pedaling during extension phase.