Rochelle Ivana De SilvaYou’re likely familiar with the idea of a circadian rhythm – your body’s 24-hour cycle that governs sleep and wakefulness. It turns out that resting heart rate also follows mysterious, long rhythms that run independently of the outside world. Resting heart rate is measured by how many beats per minute your heart makes while you’re calm and inactive. This measure is linked to stress, fatigue and fitness. Our new study, publ…