High cycling cadence reduces carbohydrate oxidation at given low intensity metabolic rate

Cycling cadence (RPM)-related differences in blood lactate concentration (BLC) increase with increasing exercise intensity, whilst corresponding divergences in oxygen uptake (VO₂) and carbon dioxde production (VCO₂) decrease. We tested the hypothesis, that a higher RPM reduces the fraction (%) of the VO₂ used for carbohydrate oxidation (relCHO) at a given BLC. Eight males (23.9 +/- 1.6 yrs; 177 +/- 3 cm; 70.3 +/- 3.4 kg) performed incremental load tests at 50 and 100 RPM. BLC, VO₂ and VCO₂ were measured. At respiratory exchange ratios (RER) <1, relCHO were calculated and the constant determining 50% relCHO (k_CHO) was approximated as a function of the BLC. At submaximal workload, VO₂ and RER were lower (p<0.001) at 50 than at 100 RPM. No differences were observed in VO_2peak (3.96 +/- 0.22 vs. 4.00 +/ 0.25 l min^-1) and RER_peak (1.18 +/- 0.02 vs. 1.15 +/- 0.02). BLC was lower (p<0.001) at 50 than at 100 RPM irrespective of cycling intensity. At 50 RPM, k_CHO (4.2 +/- 1.4 (mmol l^-1)³) was lower (p<0.05) than at 100 RPM (5.9 +/- 1.9 (mmol l^-1)³). This difference in k_CHO reflects a reduced CHO oxidation at a given BLC at 100 than at 50 RPM. At a low exercise intensity, a higher cycling cadence can substantially reduce the reliance on CHO at a given metabolic rate and/or BLC.