Millions of people now start their day with a number—a "readiness" score, a "body battery"" level or a measure of "strain""—delivered by the wearable device on their wrist or finger. But how much ...

You check your smartwatch after a run. Your fitness score has dropped. You've burned hardly any calories. Your recovery score ...

Men’s Fitness aims to feature only the best products and services. If you buy something via one of our links, we may earn a ...

Men’s Fitness aims to feature only the best products and services. If you buy something via one of our links, we may earn a commission. Heart rate variability, or HRV, is quickly becoming one of the ...