DURING INTENSE EXERCISE, OBESE WOMEN RELY MORE THAN LEAN WOMEN ON AEROBIC ENERGY

A series of untrained, healthy, obese women (body mass index 32.5 +/- 0.9 kg.m(-2)) were subjected to a protocol of intense exercise on a cy cloergometer and compared with lean controls (body mass index 20.9 +/- 0.5 kg.m(-2)). Physiological parameters, blood lactate, bicarbonate, plasma metabolites, oxygen consumption and CO2 production were measure d. Impedance-derived extracellular water and plasma changes in lactate and bicarbonate were used to determine changes in bicarbonate pools a nd lactate-displaced CO2. From these and respiratory gases, the respir atory quotient was calculated and thence overall fuel consumption. Ana erobic energy during exercise accounted for about 1.8% of all energy c onsumed in the lean but only 0.7% in the obese. Obese women fatigued a t lower workloads and energy expenditure levels than did the lean, and their lactate buildup was similar when compared on the basis of fat-f ree mass. The data support the postulation of fatigue being triggered by a combination of factors: stretched cardiovascular work would be th e main factor for obese women, in part limiting lactate production. Fo r lean women, the triggering factor for fatigue could be the loss of b uffering capacity; but it is the combination of stretching cardiovascu lar capacity, exhaustion of glycogen and available glucose and increas e in lactate/loss of bicarbonate buffer that determines the onset of f atigue.