Variability of Respiration and Metabolism: Responses to Submaximal Cycling and Running

Abstract The purpose of this investigation was to examine day-to-day variations in metabolic measurements during submaximal exercise. Ten male subjects (five cyclists, five runners) randomly performed four cycling (CYC) and four running (RUN) trials. CYC trials were conducted on a bicycle ergometer at 100 W, 150 W, and 200 W; and RUN trials at treadmill velocities of 170, 200, and 230 m/min. Oxygen consumption (VdotO 2 ) and minute ventilation (VdotE) were recorded each minute by a computer-based system. Blood lactic acid (HLA) was sampled from an antecubital vein at 3-min post exercise. No significant differences (p > .05) were found between cyclists and runners in VdotO 2 , VdotE, or HLA at any workload. The mean coefficients of total variation (CVt = SD/Xdot · 100%) for VdotO 2 were 4.42% (CYC) and 3.80% (RUN); mean CVt for VdotE were 3.86% (CYC) and 4.82% (RUN); mean CVt for HLA were 13.4% (CYC) and 16.3% (RUN). Significant day-to-day differences (p < .05) were found in VdotO 2 of cyclists during CYC and RUN, VdotO 2 of runners while CYC and RUN, and VdotE of cyclists during RUN. No significant day-to-day differences were observed for HLA. These data demonstrate the importance of considering VdotO 2 , VdotE, and HLA variability in reporting the results of experimental protocols.