Mikkelsen BM1, Zuniga JM2, Herron WK1, Frauso FE1, Pulliam AN1. The Effect of Cardiorespiratory Fitness on the Assessment of the Physical Working Capacity at the Fatigue Threshold. 1Department of Exercise Science and Pre-Health Professions, Creighton University, Omaha, NE, USA. 2Department of Biomechanics, University of Nebraska Omaha, Omaha, NE, USA.


Purpose: The purpose of this study was to determine if different cardiorespiratory fitness levels (maximal oxygen uptake or VO2max) affect neuromuscular fatigue as measured by the physical working capacity at the fatigue threshold (PWCFT). Methods: Fourteen adults (14 men; mean ± SD; age = 20.79 ± 0.89 years; body weight = 80.7 ± 10.91 kg; height = 178.4 ± 5.29 cm) volunteered to participate in the investigation. Each participant performed an incremental cycle ergometry test to fatigue while electromyographic (EMG) signals were measured from the vastus lateralis (VL) muscle. Mean, standard deviation, and range values were calculated for the power outputs determined by the PWCFT. The relationships for EMG amplitude and power output for each participant were examined using linear regression (SPSS software program, Chicago, IL). An alpha level of p ≤ 0.05 was considered significant for all statistical analyses. Results: Participants were divided in a low and high fitness levels according to their VO2max values. A paired dependent t-test was used to determine if there were significant mean differences in power outputs associated to the PWCFT test for the low (Mean ± SD 162.5 ± 90.14 W) and high (173.21 ± 49.70 W) VO2max groups. The results of the dependent t-test indicated that there were no significant mean differences (p > 0.05) between the high and low VO2max groups. The zero-order correlation for the power outputs between groups were not significantly correlated (r = 0.23). Conclusion: The results of the present investigation indicated that the cardiorespiratory fitness level does not affect neuromuscular fatigue assessment during cycling.