Spontaneous running increases VO2max and running performance in rats.

The effect of spontaneous running activity on maximal O2 consumption (VO2max), running performance, and submaximal O2 consumption (VO2submax, running economy) was studied in rats to determine whether this exercise mode can produce significant training adaptations. Twenty male Long-Evans rats (300 +/- 20 g) were housed in spontaneous activity running wheels, and after 8 wk they were divided into high-, average-, and low-performing groups according to the average spontaneous running distance and tested for maximal running performance, VO2max, and VO2submax. The average-performing rats ran 52% longer than the control rats (P less than 0.01) and 19% longer than the low-performing rats (P less than 0.05). There was no difference in maximum running time to exhaustion between the average- and high-performing rats. The low-performing rats ran 28% longer than the control rats (P less than 0.05). The VO2max of the average-performing rats was 12% greater than in the control rats (P less than 0.01). There were no differences in VO2max between either low-performing and control rats or between average- and high-performing rats. Although the VO2submax was not different between low-, average-, and high-performing rats, in all three groups it was lower than in the control rats (P less than 0.01). Accordingly, we recommend that only those Long-Evans rats that, on average, spontaneously run greater than 11.6 km/wk for a minimum of 8 wk be considered to have undergone a training effect. Rats that perform poorly can be identified as early as 2 wk after the start of training.