Exercising at 70 – 80% of max HR is the optimal zone for maximum endorphin release.

Aerobic exercise is known to activate the body’s stress response, the hypothalamic-pituitary-adrenal (HPA) axis, and yet many people engage in sports like running because they perceive its effects as relaxing. Solving this apparent contradiction calls for a distinction between “good stress” and “bad stress,”…
Full article 😺 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4703784/