Effects Of Cycling Cadence And Power Output Oscillation On Performance, Lactate And Acid-base Status

Expert cyclists prefer cadences (RPM) of 80-110 RPM, while research suggests 50-80 RPM to be more efficient. A higher RPM causes greater changes in plasma lactate (PLC) and acid-base status and stimulates a faster response in ventilation. Laboratory studies assessing the effects of RPM commonly use constant power profiles (C). C does not represent realistic performance requirements, where power output shows oscillations (OSC). OSC increase the freely chosen RPM. Thus, a higher RPM may be advantageous in terms of time to exhaustion (TTE) at high intensity power output during OSC. PURPOSE: To test the hypothesis that a higher RPM reduces an OSC-related decrease in TTE due to a more effective respiratory compensation of the corresponding metabolic acidosis at higher PLC. METHODS: 14 male cyclists (age 27.7±4.9 yrs; height 183±6.3 cm; body mass 77.7±8.3 kg) performed one incremental (INC) and four TTE trials at an average of 100% power output corresponding to the peak oxygen uptake (P-VO2PEAK) as calculated from the INC. TTE trials were performed at 50 and 90 RPM using a C (TTE50_C and TTE90_C) or OSC (TTE50_OSC and TTE90_OSC) load protocol. For OSC P-VO2PEAK fluctuated between 75 and 125% every 15 s. Capillary blood samples were collected from the ear lobe for PLC and acid-base status assessment. RESULTS: Main effects showed longer TTE for C (p=0.026) and 90 RPM (p=0.004) than OSC and 50 RPM, respectively (TTE50_C 389±91 s; TTE90_C 440±155 s; TTE50_OSC 333±103 s; TTE90_OSC 398±113 s). There was no interaction between RPM and load protocol. PLC was higher (p<0.001) and pH, HCO3- and pCO2 were lower (p<0.001; p<0.001; p=0.008) at TTE after 90 RPM trials (Tab.1). No difference between C and OSC or interaction with RPM was found. CONCLUSIONS: OSC and an RPM of 50 min-1 decreased TTE. Higher PLC, lower pH and higher respiratory compensation of the corresponding metabolic acidosis does not explain the observed advantage in performance at higher RPM in terms of TTE at C and OSC. Table 1 - : PLC and acid-base status at TTE; a: different from RPM 50, p < 0.05 TTE50_C TTE90_C TTE50_OSC TTE90_OSC PLC (mmol l-1) 17.3 ± 3.1 18.9 ± 2.2a 16.9 ± 3.6 19.2 ± 3.4a pH 7.177 ± 0.057 7.152 ± 0.053a 7.180 ± 0.069 7.149 ± 0.064a HCO3 - 12.3 ± 2.0 11.2 ± 1.3a 13.1 ± 2.7 11.2 ± 1.9a pCO2 33.0 ± 2.7 31.8 ± 4.1a 34.7 ± 4.1 32.0 ± 3.2a