HANCOCK, T.V.*; GLEESON, T. T.: The tradeoff between endurance and metabolic costs using intermittent locomotion in the desert iguana (Dipsosaurus dorsalis).

The elevated O₂ consumption (VO₂) observed during recovery from activity incurs additional metabolic costs to the animal beyond that seen during activity. These costs are also realized during intermittent activity, alternating exercise and rest, where VO₂ is high during rest. Utilizing a rapid fatiguing exercise intensity (4x maximum aerobic speed=1.08 m/s), Dipsosaurus (n=10) were run for varying durations (5, 15 or 30 sec) and pauses (1, 2, 4 or 8 x the activity period). Distance capacity, the total distance summed from all activity intervals and reflecting endurance, increased significantly versus continuous locomotion for most protocols. The largest increases were seen when the activity period was limited to 5 sec and the pause period was extended to 5, 20 and 40 sec (55, 118 and 193 m). To assess the metabolic costs incurred from these regimens enabling increased endurance, VO₂ was measured for six periods of 5 sec activity separated by either 5, 20, or 40 sec (n=8). The total excess oxygen consumption (TEOC) was measured as the sum of additional O₂ consumption during activity, pauses and recovery. TEOC increased significantly from 0.08 to 0.09 and 0.12 ml O₂/g, respectively. As animals traveled the same distance for all 3 regimens, the most expensive strategy per distance traveled was also the one which provided the greatest endurance. The increase in TEOC was primarily due to a significant increase in O₂ consumed during pause intervals as pause duration increased, while recovery VO₂ did not differ significantly. The concomitant increase in endurance seen is possibly due to a larger repletion of metabolites or elimination of end products during longer rest periods allowing additional bouts of activity to be performed. NSF#97240140.