Load and Velocity of Contraction Influence Gross and Delta Mechanical Efficiency

Abstract

The effects of three different cadences and five different work rates on Gross (GE) and Delta Efficiency (DE) during cycle ergometry were studied. Fifteen well-trained cyclists exercised for 30 minutes at 60, 80, or 100 RPM on three different occasions. On each occasion, the load was increased every five minutes and corresponded to approximately 50, 60, 70, 80 and 90% of V̇O₂max. During the last three minutes of each stage, steady-state energy expenditure was calculated while work rate was recorded. In addition, the oxygen cost of unloaded cycling (CUC) was also measured. GE was calculated as the ratio of work rate to the rate of energy expenditure, whereas DE was calculated as the reciprocal of the slope of this relationship at work rates between 50 and 90% of V̇O₂max. The CUC corresponded to 0.66±0.03 l/min, 0.77±0.04 l/min and 1.04±0.04 l/min at 60 RPM, 80 RPM and 100 RPM, respectively (p<0.01 for all comparisons). GE was similar at all cadences when cycling at 80 and 90% V̇O₂max. DE increased with increasing rpm and corresponded to 20.6±0.4%, 21.8±0.6%, and 23.8±0.4% at 60 RPM, 80 RPM and 100 RPM, respectively (p<0.01 for all comparisons). Therefore, when trained cyclists exercise intensely (80-90% V̇O₂max), GE is similar at cadences of 60, 80 and 100 RPM, despite the significant increase in the CUC. Thus, it is possible that delta efficiency increases with increasing cadence.

Key words

Physical exercise - muscle energetics - actin - myosin - series elastic elements - caloric expenditure