Is there a conflict between minimizing effort and energy expenditure with increasing velocities of muscle contraction in humans?

Abstract

1. The present study examined the possibility that minimizing effort conflicts with minimizing energy expenditure at different velocities of muscle contraction during cycling. 2. Six normal subjects underwent incremental exercise on an electrically stabilized cycle ergometer. Power output increased by 45 W every 3 min to exhaustion at pedalling frequencies of 40, 60, 80 and 100 r.p.m. on separate days. Energy expenditure (oxygen uptake), leg effort and dyspnoea (Borg 0-10 scale) were measured in parallel at the end of each minute. 3. All six subjects completed 10 min of exercise achieving 180 W for all four pedalling frequencies. Two-way analysis of variance indicated that oxygen uptake (P < 0.0001), leg effort (P < 0.0001) and dyspnoea (P < 0.0001) increased with duration of exercise and power output; oxygen uptake (P < 0.0001) and leg effort (P < 0.05) were significantly different between pedalling frequencies; the interactions were not significant. Oxygen uptake was minimal at 60 r.p.m., and increased at both higher and lower pedalling frequencies. Both leg effort and dyspnoea were minimal at 80 r.p.m.; leg effort intensified at higher and lower pedalling frequencies; and dyspnoea was most intense at 100 r.p.m. 4. There was a conflict between minimization of energy expenditure and leg effort at power outputs less than 180 W. Minimizing effort occurred at the expense of an increase in energy expenditure.