Assessment of methods for assigning treadmill exercise workloads for lean and obese women.

The use of relative oxygen consumption (% VO2 max) to equate workloads between trained and untrained subjects is considered appropriate. Whether this method (% VO2 max) is correct when testing lean versus obese subjects has not been studied. Using three experimental sessions separated by at least one week we studied seven obese, nondiabetic women weighting 140 +/- 21 kg (mean +/- s.d.) and 10 lean women of similar age weighing 51 +/- 5 kg during treadmill walking. Body fat determined by hydrostatic weighing was 50 +/- 7 and 23 +/- 7 percent in obese and lean groups, respectively (P less than 0.05). Absolute maximal VO2 (VO2 max) in obese women (3.18 +/- 0.28 l/min) significantly exceeded VO2 max for lean women (2.45 +/- 0.31 l/min, P less than 0.05). However, in obese women VO2 max relative to total body weight (TBW) was lower (P less than 0.05) while VO2 max relative to fat-free weight (FFW) was similar to corresponding values for lean women. Submaximal treadmill exercise at 75m/min with 0, 5 and 10 percent inclines resulted in higher VO2 (l/min) and heart rate (HR) in the obese group (P less than 0.05). At each incline VO2 relative to BW was significantly lower in the obese (P less than 0.05) yet significantly higher when expressed relative to FFW (P less than 0.05). The relationship between HR and %VO2 max was similar for lean and obese. Ten minutes of walking at 70% VO2 max resulted in no significant differences between the groups in the 10 min values for HR, total work done, rise in rectal temperature, plasma lactic acid, perceived exertion and oxygen consumption relative to FFW. We conclude that either fixed absolute workloads or fixed oxygen consumption (absolute or relative to BW or FFW) are inappropriate methods for equating workloads when lean and obese subjects are compared. Relative VO2 accurately defines physiologically comparable exercise intensities for these groups and this should be the method of preference when studies are designed to investigate metabolic, endocrine or cardiovascular similarities and/or differences between these groups.