Energetics of sinusoidal exercise below and across critical power and the effects of fatigue.

PURPOSE

Previous studies investigating sinusoidal exercise were not devoted to an analysis of its energetics and of the effects of fatigue. We aimed to determine the contribution of aerobic and anaerobic lactic metabolism to the energy balance and investigate the fatigue effects on the cardiorespiratory and metabolic responses to sinusoidal protocols, across and below critical power (CP).

METHODS

Eight males (26.6 ± 6.2 years; 75.6 ± 8.7 kg; maximum oxygen uptake 52.8 ± 7.9 ml·min·kg; CP 218 ± 13 W) underwent exhausting sinusoidal cycloergometric exercises, with sinusoid midpoint (MP) at CP (CP) and 50 W below CP (CP-50). Sinusoid amplitude (AMP) and period were 50 W and 4 min, respectively. MP, AMP, and time-delay (t) between mechanical and metabolic signals of expiratory ventilation ( ), oxygen uptake ( ), and heart rate ( ) were assessed sinusoid-by-sinusoid. Blood lactate ([La]) and rate of perceived exertion (RPE) were determined at each sinusoid.

RESULTS

AMP was 304 ± 11 and 488 ± 36 ml·min in CP and CP-50, respectively. Asymmetries between rising and declining sinusoid phases occurred in CP (36.1 ± 7.7 vs. 41.4 ± 9.7 s for t and t, respectively; P < 0.01), with unchanged ts. MP and RPE increased progressively during CP. [La] increased by 2.1 mM in CP but remained stable during CP-50. Anaerobic contribution was larger in CP than CP-50.

CONCLUSION

The lower aerobic component during CP than CP-50 associated with lactate accumulation explained lower AMP in CP. The asymmetries in CP suggest progressive decline of muscle phosphocreatine concentration, leading to fatigue, as witnessed by RPE.