Yep—resting heart rate is a good proxy, and readily measurable from Apple Watch.<p>A definitive study would randomly assign people to an exercise routine, follow them for 20-30 years, and then measure hard outcomes like heart attacks, strokes, and all-cause mortality.<p>Since that&#x27;s pretty challenging, all of the studies on exercise (and nutrition, for that matter) make two types of approximation:<p>1. analyze correlations in data rather than randomize, and&#x2F;or<p>2. analyze proxy metrics like resting heart rate or blood pressure rather than hard endpoints.<p>That&#x27;s part of what makes research on health so complex!