ZANI, P.A.*; SIDENBLAD, K.; VAN DIJCK, A.; GLEESON, T.T.; KRAM, R.; University of Colorado: Low metabolic cost of level locomotion in box turtles (Terrapene ornata): why so inexpensive?

One species of semi-aquatic turtle has been shown recently to walk with remarkable metabolic economy. We have begun to investigate if turtles in general are economical walkers and if so why. We measured the metabolic cost of locomotion in ornate box turtles, Terrapene ornata. Over a period of two weeks we trained turtles to walk steadily on a treadmill for 10-20 minutes while wearing a mask. We then measured steady-state oxygen consumption for 5-10 trials of level walking (avg. speed � 1 S.D. = 0.07 � 0.005 m/s). Minimum cost of transport (8.0 � 2.97 J/kg/m) was roughly one-half the expected value (15.9 � 1.50 J/kg/m) for animals of similar size. We also collected data from animals walking up a 24� incline. Turtles walked much slower (0.04 � 0.016 m/s) and with a much higher cost of transport (15.0 � 7.10 J/kg/m). By matching level and incline trials of similar speed we were able to calculate locomotor efficiency (20.2 � 9.16 %). This value is comparable to terrestrial mammals and birds of similar size. Thus, the low cost of transport during level walking does not appear to be due to high efficiency of turtle muscle, although tortoise muscle in vitro is uniquely efficient (35 %). We also collected the ground-reaction forces of these same individuals walking on a force platform. These data will determine whether economical walking in box turtles is due to mechanisms of energy conservation (inverted pendulum).

Supported by NIH F32 AR08615 to PAZ.