A life-history perspective on exercise

Exercise has been extensively studied in humans because of its multiple benefits, yet it is unclear how relevant 'exercise' is to non-human animals and whether the effects of exercise are identical to those in humans. One main difference is that humans rarely have chronic limited resources when exercising, whereas wild animals do. Nevertheless, because other species from fish to lizards have been shown to have similar responses to exercise, the generalized response is almost certainly very old evolutionarily. This means that the response to exercise evolved under conditions of limited resources, and the modern conditions under which humans use exercise are novel. If we view 'exercise' as increased locomotor activity above baseline levels, then locomotor performance and the response to exercise play a crucial role within the larger life-history strategies of animals. We consider exercise from a life-history perspective, where allocating finite resources towards the exercise response can create trade-offs with other traits. In this Review, we synthesize our work on green anole lizards (Anolis carolinensis) to show how complex trade-offs can occur when resources are forced to be allocated to performance via specialized exercise training. There is still much we do not know about the exercise response of vertebrates, and future studies would benefit by considering exercise from a life-history perspective.