Relationship between pedal force asymmetry and performance in cycling time trial.

AIM: It remains unclear if cyclists with better performance have less asymmetry. Therefore, this study aimed at assessing the relationship between cycling time trial performance and bilateral asymmetries in pedal forces.
METHODS: Ten cyclists/triathletes performed an incremental cycling test to exhaustion to measure maximal oxygen uptake and power output. In a second session, bilateral pedal forces were acquired during a 4-km cycling time trial on the stationary cycle ergometer. Resultant and effective forces were computed along with the index of effectiveness at 500 m sections of the time trial using instrumented pedals. Intra-limb variability and the asymmetry index were calculated for each force variable.
RESULTS: Multivariate analysis assessed bilateral differences in pedal forces accounting for power output, pedalling cadence and oxygen uptake of each cyclist. Force variables did not change throughout the test (effective - P=0.98, resultant - P=0.90 and index of effectiveness - P=0.99) with larger force applied by the dominant limb (11-21%). The relationship between asymmetries and performances was strong for the effective force (r=-0.72) but weak for the resultant force (r = 0.01) and for the index of effectiveness (r=-0.29). Substantial asymmetries were observed for the effective force (36-54%), resultant force (11-21%) and for the index of effectiveness (21-32%) at greater range than intra-limb variability (effective force =8-22%, resultant force =5-10% and index of effectiveness =1-3%).
CONCLUSION: Larger asymmetries in effective force were related to better performances during the 4-km time trial with low intra-limb variability for force measures suggesting consistence in asymmetries for individual cyclists.