Author(s): MACDOUGALL, K., ABOODARDA, S., WESTERGARD, P., MACINTOSH, B., Institution: UNIVERSITY OF CALGARY, Country: CANADA, Abstract-ID: 618

INTRODUCTION:
During constant power cycling in the heavy and severe domains, the steady-state VO2 is delayed or prevented due to the VO2 slow component (SC). The rising oxygen uptake has been assumed to represent a progressive loss of muscle efficiency, resulting primarily from skeletal muscle fatigue, however evidence for a causal relationship is equivocal. Notably, it has also been demonstrated that alterations in pedaling technique may occur during fatiguing cycling exercise. If these alterations impair cycling efficiency, this could represent a moderating factor between the development of fatigue and the increase in oxygen cost observed with the SC. However, little is known about the existence of pedaling technique adjustments during fatiguing cycling exercise in association with the SC. Therefore, the purpose of this study was to explore the association between the VO2 SC and skeletal muscle fatigue, and the impact that changes in pedaling technique may have on the development of the VO2 SC.
METHODS:
Eleven participants completed an incremental exercise test to determine lactate threshold, followed by constant power trials to exhaustion at 10% above lactate threshold (power output 194 ± 55W). Utilizing femoral nerve stimulation and instrumented pedals, muscle fatigue was assessed, along with oxygen uptake, quadriceps oxygenation, electromyography (EMG), and pedal force components. To explore the temporal relationship between muscle fatigue and the appearance of the SC, Pearson’s correlation coefficient was calculated between the relative reductions in twitch force across the first 2.5 min of exercise and the time of onset of the SC. To explore the association between the SC and alterations in pedaling technique, repeated measures correlations between physiological and mechanical variables were estimated at both a group and individual level.
RESULTS:
There was no significant correlation between the time of onset of the VO2 SC and initial reductions in twitch force (r = -0.076, p = 0.852). At a group level, the SC (387 ± 172 ml/min at peak) was significantly correlated with quadriceps twitch force (r = -0.48, p < 0.001), root mean square EMG (r = 0.18, p = 0.016), and muscle oxygenation (r = -0.50, p < 0.001), as well as with pedaling mechanical variables such as peak total downstroke force (r = -0.16, p = 0.022), minimum total upstroke force (r = -0.15, p = 0.029), and upstroke index of effectiveness (r = 0.18, p = 0.012). However, there was large interindividual variability for all these correlations. At an individual level, repeated measures correlations between twitch force and the SC ranged from -0.03 to -0.87, while correlations between the SC and some pedaling mechanical variables were seen to be as high as 0.80 for some individuals.
CONCLUSION:
From the heterogeneity of the data, we question a direct causal link between fatigue and the SC, and suggest that alterations in pedaling technique may also be a factor in its development.