The influence of the muscle fiber pennation angle and innervation zone on the identification of neuromuscular fatigue during cycle ergometry

The purpose of the present investigation was to compare the electromyographic (EMG) responses and the estimated physical working capacity at the fatigue threshold (PWCFT) values recorded from electrode arrangements placed: (1) parallel to the muscle fiber pennation angle (MFPA), (2) parallel to the long axis of the femur, and (3) over the innervation zone (IZ) during incremental cycle ergometry. Thirteen college-aged males and females (mean age ± SD = 22.4 ± 3.4 years) performed an incremental test to exhaustion on a cycle ergometer. A linear electrode array was utilized to determine the MFPA and location of the IZ of the vastus lateralis (VL). For determination of the PWCFT values, EMG signals were recorded from three bipolar electrode arrangements at different locations over the VL. The results of a one-way repeated measures ANOVA indicated there were no significant (p < 0.05) mean differences in PWCFT values among the electrode arrangements (parallel to the MFPA = 190 ± 36 W; parallel to the long axis of the femur = 194 ± 40 W; and over the IZ = 199 ± 51 W) or the EMG amplitude and MPF values at the common power outputs. There were also significant correlations (r = 0.75-0.91) among the three electrode arrangements for PWCFT values. These findings suggested that the PWCFT, like absolute EMG amplitude and MPF, is robust to the influence of electrode placement over the IZ as well as the orientation with respect to the MFPA during cycle ergometry.