 Resting heart rate, RHR, is a reliable indicator of cardiovascular health and can be used to assess overall fitness levels. Studies show that RHR decreases with increasing levels of physical activity and increases with age. Additionally, RHR is affected by body fat percentage and weight, suggesting that it may be a useful tool for population-level monitoring. This article was authored by Tomas I. Gonzalez, Justin Y. John, Timothy Lindsay, and others.