Evidence is mounting that even tiny amounts of intense exercise can aid health.Credit...Getty Images9. Comically brief weight training could make you stronger.In a small-scale new study, men and women who contracted their arm muscles as hard as possible for a total of three seconds a day increased their bicep strength by as much as 12 percent after a month.They repeated this routine once a day, five times a week, for a month, for a grand total of 60 seconds of weight training. It changed their biceps in ways that were slight but biologically meaningful, especially for people new to weight training.The findings add to mounting evidence that even tiny amounts of intense exercise, like four seconds of strenuous biking or 10 seconds of all-out sprinting, can aid health.

Multiply that number by 85 percent to roughly approximate an effort cap for easy runs (though adjusting to a different percentage if you feel like that’s a bit too hard or too easy).