Sustained swimming al: 0.9 BL s(-1), where BL is fork body length, followin
g a bout of exhaustive exercise enhanced recovery of metabolite;and acid-ba
se status in rainbow trout compared with fish held in still water. The most
striking effect of an active recovery was a total absence of the elevation
cortisol concentration typically associated with exhaustive exercise. In f
ish swimming at 0.9 BL s(-1), plasma cortisol levels averaged 20-25 ng ml(-
1) throughout the 6h recovery period. In contrast, plasma cortisol increase
d to a peak level of 128.4+/-11.2 ng ml(-1) (mean +/- S.E.M., N=6) in fish
recovering in still water. Muscle glycogen was completely resynthesized and
lactate cleared within 2h of exercise in swimming fish compared with more
than 6h required in the fish held in still water. Similarly, blood lactate
level and acid-base status were restored more quickly in the swimming fish.
These observations suggest that the prolonged recovery usually associated
with exhaustive exercise in rainbow trout is due to elevations in plasma co
rtisol concentration and that the stimulus for cortisol release is not exer
cise ger se, but rather postexercise inactivity.