This would have been my prior about aerobics ...

"The Economics of Aerobics"
Economic Inquiry, Vol. 52, Issue 1, pp. 201-204, 2014

KEMPER MORELAND, Eastern Michigan University
Department of Economics

This study presents a simple model that weighs the benefits and costs of aerobic exercise to the individual. The model assumes that adding years to life serves as the primary benefit of exercise, and that hours of exercise over a lifetime serve as the cost. Given previous estimates of individual rates of time preference this study finds that people act rationally when they choose to watch a track event rather than choose to run themselves.

Gated version here.