The Influence of Electrode Placement on the Physical Working Capacity At the Fatigue Threshold

Abstract

PURPOSE: To examine the influence of electrode placement on the physical working capacity at the fatigue threshold (PWCFT). The PWCFT test estimates the highest power output that can be maintained without neuromuscular evidence of fatigue and is determined from the rate of increase in the amplitude of the electromyographic (EMG) signal. METHODS: Fifteen college-aged males and females (mean age ± SD = 22.6 ± 3.4 yr; BW = 74.3 ± 11.2 kg; HT = 176.1 ± 9.0 cm) performed an incremental test to exhaustion on a cycle ergometer. A linear electrode array was utilized to determine the location of the innervation zone (IZ) and muscle fiber pennation angle (MFPA) of the vastus lateralis (VL). For determination of the PWCFT values, surface EMG signals were recorded from 3 bipolar electrode arrangements at different locations over the VL during the incremental tests. The first electrode arrangement was placed on the VL at one-third of the distance between the lateral border of the patella and the anterior superior iliac spine, and oriented parallel to the MFPA. The second electrode arrangement contained the same center point as the first electrode arrangement, but was oriented parallel to the long axis of the femur. A third electrode arrangement was placed over the IZ and oriented parallel to the MFPA. RESULTS: The results of a one-way ANOVA indicated there were no significant (p < 0.05) mean differences in PWCFT values among the 3 electrode placements (parallel to the MFPA = 181 ± 40 W; parallel to the long axis of the femur = 185 ± 44 W; and over the IZ = 189 ± 54 W). In addition, there were significant correlations in PWCFT values for the electrode placement parallel to the MPFA vs. parallel to the long axis of the femur (r = 0.94) and over the IZ (r = 0.88), as well as for the electrode placement parallel to the long axis of the femur vs. over the IZ (r = 0.81). CONCLUSIONS: These findings indicated that the PWCFT test is not influenced by the placement of a bipolar electrode arrangement in relation to the MFPA or over the IZ. Practical Applications: The results of the current study suggested that the onset of neuromuscular fatigue (PWCFT) can be estimated without identification of the MFPA or IZ.