EFFECTS OF EXERCISE AND DIET ON ...

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Crompton, A. W. Harvard University; Cambridge, MA. USA. The argument, that ectotherms cannot grow and remodel their bones to the extent that endotherms do ...
EFFECTS OF EXERCISE AND DIET ON BONEBUILDING: A MONITOR CASE. Owerkowicz, T and Crompton, A. W. Harvard University; Cambridge, MA. USA

The argument, that ectotherms cannot grow and remodel their bones to the extent that endotherms do, was investigated in monitor lizards (Varanus exanthematicus). When maintained at a constant 35- 37°C on ad libitum diet, monitor lizards are capable of sustained growth at rates of

1 O g/day, equal to those of similarly sized endotherms. As highlighted by fluorescent dyes, deposition rates (5--8 µm/day) of highly vascular, circumlamellar bone are equivalent to fibrolamellar bone of large endotherms. Recordings from multiple rosette strain gauges reveal that long bones of monitors, mammals and birds incur comparable levels of strain during moderate activity (s 1500 µstrain), with torsion more pronounced in a sprawling gait. Daily exercise results in faster growth, denser vascularity and thicker cortices: increased intensity of secondary remodelling correlates with lower growth rates of exercised animals on a restricted diet. Therefore, in monitor lizards, the relative amount of bone growth versus remodelling in response to increased strain is affected by diet In contrast to cursorial endotherms, the locomotory cost of moving limb elements is not important in lizards. This, coupled with higher safety factors and an indeterminate growth pattern, may explain why reptiles need not remodel their bones at the rates of endotherms.

1997 ICVM Conference