Aerobic and Anaerobic Energy Expenditure During Exhaustive Ramp Exercise

Ramp tests are often manipulated so that oxygen uptake is able to interpret energy expenditure in its entirety. We hypothesized that oxygen deficits during ramp exercise to exhaustion would be significant, providing a more complete description of the types of energy expenditure available for this mode of testing. Oxygen deficits were obtained during a slow ramp (681 ± 71 s) and a fast ramp (275 ± 33 s) to exhaustion. Twelve healthy men (age 35 ± 3 yrs; VO₂max 51 ± 10 ml x kg^-1 x min^-1) performed several 10 min submaximal bike rides (at or below ventilatory threshold) to determine work rate -O₂ uptake demands. Estimated O₂ demands were compared to measured O₂ uptake during each ramp test, the difference representing an oxygen deficit. Work levels were controlled and measurements collected with a commercially available electrically braked bike ergometer and metabolic testing system (MedGraphics, Minn., MN). Data were collected and averaged in 30 s time periods, power in watts (W), energy expenditure in cumulative O₂ (L). Using a paired t-test, cumulative O₂ uptakes were significantly lower (p = 0.0001) when measured O₂ uptakes (26.0 L ± 4.5 for slow ramp; 10.8 L ± 2.8 for fast ramp) were compared to estimated O2 demands (29.0 L ± 3.7 for slow ramp; 14.1 L ± 3.5 for fast ramp). Anaerobic energy expenditures (oxygen deficits) represented 10.8 % and 23.4 % of total energy expenditure for slow ramps and fast ramps, respectively. Comparisons of the slopes for each test condition revealed significant differences (steady state > slow ramp > fast ramp; p = 0.0001, ANOVA). We conclude that the oxygen deficit during ramp testing represents a significant part of total energy expenditure.

Key words

Anaerobic energy expenditure - energy expenditure - bioenergetics