Energy Costs of Walking and Running Gaits and Their Aerobic Limits in Golden-Mantled Ground Squirrels

We studied locomotion of field-caught golden-mantled ground squirrels (Spermophilus saturatus) on a motorized treadmill that was incorporated into a respirometry system. The animals shifted gaits, from walking to trotting, at about 0.8 m/s and from trotting to galloping at 1.2 m/s; they ran as fast as 3 m/s (10.8 km/h) on our treadmill. Because we were able to determine oxygen consumption instantaneously, we observed rates of energy expenditure that accompany brief bouts of locomotion at speeds higher than those of previous studies. The slope of equations describing oxygen consumption (V̇o2, in ml/g· h) in relation to speed (m/s) differ significantly (P < .02) for walking and running (running = trot and gallop combined): walking (V̇o2 = 2.91 + 3.80 × speed), running (V̇o2 = 5.76 + 1.41 × speed). The animals thereby experience less incremental increase in rate of energy expenditure with increased speed when running than when walking. We conclude that with a maximum aerobic metabolic rate (V̇o2max) of about 10 ml/g · h, which occurs at a speed of 3 m/s, most of the spontaneous running by the ground squirrels observed under natural conditions should occur without the use of anaerobic respiration.