Effect of age and pedalling rate on cycling efficiency and internal power in humans

Abstract.

The present study was undertaken to examine the effect of age and pedalling frequency on metabolic internal power (MP_int) and delta efficiency (ΔE), defined as the ratio of the change in external work accomplished to the change in energy expended, during sub-maximal exercise on a cycle ergometer. A group of 11 children [mean age (SD)][10.6 (1.0) years] and 12 adults [23.6 (3.0) years], all cyclists, performed two incremental tests at 60 rpm and 90 rpm in a randomised order. External power (EP) was measured as the product of friction load and pedalling frequency. Oxygen consumption ($\dot V{\rm O}_{\rm 2}$ ) was measured using the Douglas bag method and an energy equivalent of 20.6 kJ·lO₂ ^–1 was used to convert $\dot V{\rm O}_{\rm 2}$ into metabolic power (MP). Linear relationships were drawn between MP and EP (MP=aEP+b) to enable the calculation of ΔE (1/a) and MP_int (b). All coefficients of determination were greater than 0.97. The results showed that children and adults increased their ΔE with the increase in pedalling rate [27 (6)% to 36 (5)%, P<0.05 in children and 27 (3)% to 30 (2)%, P<0.05 in adults]. Likewise, net MP_int (MP_int minus basal metabolism) expressed relative to total leg volume was higher at 90 rpm compared to 60 rpm [16.5 (5.0) W·l^–1 and 4.2 (2.0) W·l^–1, P<0.05, respectively, in children and 7.4 (3.0) W·l^–1 and 5.0 (2.5) W·l^–1, NS, respectively, in adults]. At 60 rpm, children and adults showed the same ΔE and net MP_int values. At 90 rpm, children showed significantly higher ΔE and net MP_int compared to adults. This study demonstrated that ΔE and net MP_int are equally influenced by increasing pedalling rate in children and adults. Furthermore, it was hypothesized that differences between children and adults at 90 rpm could be related to different anthropometric characteristics.