Photography Byron Martin / James Leighton Burns / Daniel Repeti / jphnnie4k / Getty Images
Tracking your fitness progress is a pretty straightforward business if you record the weights you lift or take advantage of specially designed watches or apps. But the type of data you can get isn’t quite as good at showing how healthy you are. Visceral fat, the type that is around your organs, for example, isn’t easily detected, and cholesterol can be high regardless of how often you exercise.