Muscle fatigue, pedalling technique and the VO2 slow component during cycling

Above the first lactate threshold, the steady-state V-O2 is delayed or prevented due to the V-O2 slow component (V-O2SC). This phenomenon has been associated with muscle fatigue, but evidence for a causal relationship is equivocal. Moreover, little is known about the contribution of pedalling technique adjustments to V-O2SC during fatiguing cycling exercise. Eleven participants completed constant power trials at 10% above the second lactate threshold. Muscle fatigue was assessed, utilizing femoral nerve stimulation and instrumented pedals, while V-O2, quadriceps oxygenation, electromyography (EMG) and pedal force components were measured. Correlations between physiological and mechanical variables were estimated at group and individual levels. Group correlations revealed moderate values for V-O2SC with quadriceps twitch force (r = -0.51) and muscle oxygenation (r = -0.52), while weak correlations were observed for EMG amplitude (r = 0.26) and EMG mean power frequency (r = -0.16), and with pedalling mechanical variables such as peak total downstroke force (r = -0.16), minimum total upstroke force (r = -0.16) and upstroke index of effectiveness (r = 0.16). The findings here align with prior literature reporting significant correlations between the magnitude of muscle fatigue and that of V-O2SC, although there was large interindividual variability for all the reported correlations. Considering the heterogeneity in the data, it is difficult to determine the relative impact of pedalling technique adjustments on V-O2SC overall, but the present study opens the possibility that in some cases, increases in V-O2 secondary to technical adjustments may be 'superimposed' on the underlying V-O2SC.