Aerobic capacity estimated by exercise vs cold-exposure: endurance training effects in rats

Two widely used measures of aerobic capacity, the maximal rate of oxygen consumption elicited by exercise (VO2max(ex)) and that induced by cold-exposure (VO2max(cold)), were compared before and after a six-week endurance training period in rats. A laddermill was used to elicit by running VO2max(ex) in a few attempts without training. Endurance training was incremented to achieve 85% of the weekly measured VO2max(ex) during the 25 min/day, 5 days/week sessions. Additional rats were left untrained either as controls or for weekly VO2max(ex) measurement. Mean VO2max(ex) was significantly greater by 34% and 20% (VO2max(ex)Mb, 29% and 9%) in the trained and weekly run groups, respectively, but no differences were found in either VO2max(cold) or body mass. Both training and the measurement of VO2max by exercise were sufficient to elevate VO2max(ex) but the enhancement of cold-exposure VO2 reported by others after endurance training was not apparent in VO2max(cold). Thus, the thermogenically-based VO2max(cold) did not reflect the adaptation to endurance training shown by exercise-elicited VO2max. We conclude that VO2max(ex) and VO2max(cold) cannot be used interchangeably as measures of aerobic capacity.