Measure of efficiency and knee isokinetic strength in bike messengers and non-cyclist athletes

Introduction: Gross efficiency (GE) appears to be correlated with strength. The purpose of this study was to investigate GE at 4 different pedaling rates (60, 70, 90, 100 rpm) and its relationship with maximal strength in a population of 8 bike messengers (BMs) and 8 experienced non-bicycle messenger (NBMs) athletes. Methods: Each of the 8 BMs, (mean age, 25.2 years ±3,2), who work in at a delivery company, who ride 218.7 (±65.1) km/week, and participate in an average of 19.6 (±11.1) hours of sport related exercise per week, and the 8 NBMs, (mean age 25.4 years ±2.2), who ride an average of 5 (+ 14.1) km/week and participate in an average of 6.5 (±3.8) hours of sport related exercise per week underwent 2 laboratory sessions. The first laboratory session determined Maximum Aerobic Power (MAP) and maximal oxygen consumption (VO2max) with steps of 30W/min. The second session included an efficiency test at 50% of MAP. GE, oxygen consumption (VO2), heart rate (HR) and Blood Lactate Concentration (BLC) were measured at four randomly selected cadences (60,70,90,100 rpm). The subjects then underwent an isokinetic test, 5 repetitions at 60°/sec and 20 repetitions at 120°/sec, to measure concentric strength for extension and flexion of both knees. Fatigability and peak torque/body weight ratio were then calculated. Results: A difference in GE (at 60, 90 100rpm), BLC (all cadences) and MAP/kg in favor of BMs was found (all P-value<0.05). No difference in VO2/VO2max (all cadences) was found (p-value>0.05). The most efficient cadence was 60 rpm in both groups. Increased cadence resulted in decreased GE and increased HR and VO2 in both groups. BLC only increased in the NBMs group. In both groups, a clear relationship between MAP/kg and low BLC was found. NBMs were found to have stronger hamstring muscles than BMs (p-value: 0.038). Few relationships between GE at different cadences, peak-torque/Bw or muscle fatigability were found. Discussion/Conclusion: BMs had a higher GE than NBMs. These results are in line with previously described analyses and are explained by higher aerobic capacity, better training status, different muscle fiber type, and better pedaling technique. At the same power output, anaerobic glycolysis, which is linked to lower economic GE, plays a greater role for NBMs. Stronger hamstring muscles of the NBMs might be explained by the diversity of their practiced sports and therefore their use of a greater diversity of muscle groups. Isokinetic knee maximal strength and fatigability was not linked with GE. Thus, isokinetic strength testing is not a good choice for evaluating GE in cycling