EPOC AND THE ENERGETICS OF BRIEF LOCOMOTOR-ACTIVITY IN MUS-DOMESTICUS

Excess post-exercise oxygen consumption (EPOC) is normally not conside red in determinations of the metabolic cost of activity. This approach overlooks an important energetic cost that an animal incurs as a resu lt of activity. To examine the importance of EPOC, we determined I-low the energetic cost of locomotion was affected by activity of short du ration and high intensity. Mice were run at maximum speed on a treadmi ll while enclosed in an open-flow respirometry system. After sprinting for 5, 15, 30, or 60 sec, each mouse was allowed to recover while rem aining enclosed in the respirometry chamber. Exercise oxygen consumpti on (EOC), the volume of oxygen consumed during the exercise, increased linearly with sprint duration. EPOC was determined as the volume of o xygen consumed after exercise ended until rest was reached. EPOC volum es were found to be constant following 5-60 sec of activity and accoun ted for greater than or equal to 90% of the total metabolic cost. The average EPOC volume of all treatments was 0.76 +/- 0.456 ml O-2 . gm(- 1). The net cost of activity (C-act), which considers both EOC and EPO C, decreased as sprint duration increased and varied between 500 ml O- 2 . g(-1) . km(-1) for 5 sec to 30 ml O-2 . 1 g(-1) km(-1) for 60 sec of activity. The values for C-act were 15 to 250 times higher than tra ditional estimates of locomotor casts. From these data, it can be conc luded that (1) EPOC is not affected by short exercise durations; (2) E POC is an important energetic consideration when exercise durations ar e short; and (3) the metabolic costs of brief, vigorous locomotion may be much higher than previously estimated. (C) 1998 Wiley-Liss, Inc.