If you’re looking for a down-and-dirty workout that gives a high payoff for a minimal time commitment (a.k.a. the busy parent’s dream), high-intensity interval training (HIIT) is the way to go. Designed to get your heart rate up to between 85% and 95% of its max effort for 15- to 20-minute spurts, HIIT is ideal when you want results but don’t have an hour a day to devote to the gym. There are many variations on the HIIT workout, but they all entail a short burst of serious effort followed by a short rest. Basically, you’re cramming an hour’s worth of moderate effort into high-output sprints, generally a 1:1 work-to-rest ratio. But if you find it impossible to finish a HIIT routine within that arrangement, you’re free to double the rest to get the most from your session. Either way, it’s one of the best short-on-time big-on-results workouts around.