Power output and mechanical efficiency of human muscle in maximal cycle ergometer efforts at different pedalling rates

Abstract

The aim of this work was to verify the hypothesis that the lowering of the pedalling rate (elicited by the increase of the exterior load) during maximal efforts performed with identical work amount causes the growth of the generated power (until the maximal values are reached) and next its fall and does not influence the gross and net mechanical efficiency changes. The above experiment was conducted with 13 untrained students who performed 5 maximal efforts with the same work amount. The first was the 30 s maximal effort (Wingate test) with the load equal 7.5% of the body weight (BW). The amount of work performed in this test was accepted as the model value for following tests to achieve. Every 3 days, each examined had next trials consisting of maximal efforts on the cycle ergometer with loads of: 2.5, 5, 10, 12.5% BW and lasting until the value of power reached in the 30 s Wingate test occurred. Changing of the external load elicited various pedalling velocity. The force-velocity (F-v) and power-velocity (P-v) dependence was calculated for every examined subject basing on the results of performed maximal efforts. The maximal power (Pmax) and optimal velocity (vo) were calculated basing on the P-v relationship depicted with the second order polynomial equation. The gas analyser (SensorMedics) equipped with the 2900/2900c Metabolic Measurements Cart/System software was used as for the oxygen output measuring during maximal efforts performance and in the resting phase. The ventilation and gas variable changes were monitored breath-by-breath in the open ventilation system. The POLAR-SportTester was used for the heart retraction (HR) measurement during both: efforts and resting. The capillary blood was taken from the fingertip before the test and: immediately after it, every 2 min for the first 10 min of the rest and in the 20th min of resting. The blood was used for the acid-base balance determination with the use of the blood gas analyser – Ciba-Corning 248. The average pedalling rate decreased during effort from 151.5 rpm to 80 rpm and the power grew from 293.5 W to 761 W along with the increase of the load from 2.5% to 12.5% BW. Powers varied among specific trials with the exception of values obtained with load equal 10 and 12.5% BW. The increase of the gross and net mechanical efficiency from 5.9 to 8.1% and from 12.2 to 19.0% respectively was also observed. The gross mechanical efficiency values reached by the load of 2.5% BW differed significantly in relation to values obtained in efforts with loads of 7.5, 10 and 12.5% BW. In the case of HRd (difference between HRmax and HR measured in relaxation), crucial disagreements were noticed between efforts with load of 2.5% and 12.5% BW. HRmax values did not differentiate performed trials. The mechanical efficiency and HRd did not vary significantly in trials with 5, 7.5, 10, 12.5% BW loads. Maximal efforts conducted with loads of 5% and 7.5% BW elicited similar changes of the acid-base balance in all measurements.