Can't get outside or to a treadmill? This circuit is your perfect solution; it alternates running-inspired cardio moves (low- and high-intensity) with resistance exercises to deliver even better results than you'd get from pounding pavement (or burning rubber) for an hour.
How it works: Each 5-minute set is broken down into three parts: a 3-minute, moderate-intensity jog, followed by a 1-minute, higher-intensity interval, and then a 1-minute strength move as an active recovery. Do each interval set twice. Try this workout up to 4 non-consecutive days per week, alternating it with your favorite strength plan (like this great resistance routine for runners) and/or flexibility training sessions.
If you're short on time, just do each interval once for an effective 25-minute cardio session.
You'll need: Nothing, but we recommend a timer to help keep track of the intervals.