Cadence Dependent Carbohydrate Management at Prolonged Constant Workload

Abstract

Competitive cyclists prefer cadences above 90 revolutions per minute (RPM) during racing, testing in the laboratory and training although metabolic rate and blood lactate concentration (BLC) are increased compared to 50 to 60RPM. The maximal lactate steady state (MLSS) depicts the BLC that can be maintained over time without a continual accumulation at constant prolonged workload. In cycling no difference in the MLSS was combined with lower power output related to peak workload (IMLSS) at 100 than at 50RPM. MLSS coincides with a respiratory exchange ratio (RER) close to 1. Recently, at incremental exercise an RER of 1 was found at similar workload and similar intensity but higher BLC at 100 compared with 50RPM. PURPOSE: To re-assess a potential effect of cycling cadences on the MLSS and test the hypothesis that the MLSS is higher at 105 than at 60RPM with no difference in IMLSS as input parameters for modelling potential cadence effects on whole body carbohydrate management at MLSS and endurance training relevant lactate concentrations. METHODS: MLSS and IMLSS were determined in a between-subject design (n=16; age:25.1±1.9yrs, height:178.4±6.5cm, body mass:70.3±6.5kg vs. n=16; 23.6±3.0yrs, 181.4±5.6cm, 72.5±6.2kg; Study I) and confirmed using a within-subject design (n=12; 25.3±2.1yrs, 175.9±7.7cm, 67.8±8.9kg; Study II). Modelling IMLSS and cycling at a BLC of 2.0mmol l/1 revealed cadence specific fractions of aerobic rates used for carbohydrate consumption (relCHO). RESULTS: In Study I the MLSS was lower at 60 than at 105RPM (4.3±0.7 vs. 5.4±1.0mmol/l; p=0.003) with no difference in IMLSS (68.7±5.3 vs. 71.8±5.9%. Study II confirmed these findings on MLSS (3.4±0.8 vs. 4.5±1.0mmol/l; p=0.001) and IMLSS (65.0±6.8 vs. 63.5±6.3%; p=0.421). Modelling revealed that for a given relCHO a higher BLC is required at 105 than at 60RPM indicating that steady state cycling at a BLC of 2.0mmol/l at 60RPM resulted in a relCHO of 76% compared to 58% at 105RPM. CONCLUSIONS: The higher MLSS at 105 than at 60RPM combined with an invariance of IMLSS and RER close to 1 at MLSS support the hypothesis that higher cadences can induce a preservation of carbohydrate at given BLC levels during low intensity high volume training sessions.