Are you all about saving time, getting more bang for your buck, and blasting calories? Go for sweat-dripping, fast-paced cardio sessions. If you've only got 20 minutes, then opt for one of these intense strategies instead of your normal workout.

Instead of: zoning out on the treadmill
Go for: intervals

Not only do high-intensity interval training (HIIT) workouts help you burn more calories in a shorter amount of time, but also, mixing up your pace helps you become a better, faster runner. If it's calorie burn you're after, then take note: going at your max for even just a little bit can help you burn a substantial amount of calories in the same amount of time, no matter what your running level. Alternating a steady 10-minute mile (6 mph) pace on the treadmill with five 60-second intervals at 7.5 minutes per mile (8 mph), for example, will burn 16 more calories in 20 minutes [1] for a 130-pound person than just running at a steady 10-minute-mile pace — 196 vs. 180 calories. Mix up your pace and timing as much as you want; just make sure you are pushing it for those intervals. If you've never done intervals before, here's a beginner interval treadmill workout to try [2].

Instead of: your regular circuit workout
Go for: Tabata

Tabata is a form of HIIT you can do with almost any circuit workout. It consists of four-minute blocks of intense exercises (eight rounds at 20-second intervals followed by 10 seconds of rest), and while it can make you feel ready to quit, the payoff is worth it. At 13.5 calories burned per minute [3], you'll blast through 270 calories in just 20 minutes. Try one of our Tabata workouts here [4].

Instead of: heading for the dumbbell rack
Go for: kettlebells

Need even more of a burn? A recent study by the American Council on Exercise found that the average person burns a whopping 400 calories in just 20 minutes when using the kettlebell. While it takes a little time to learn how to use kettlebells safely, swinging the weights around can save you a lot of time in the gym. Get going with these kettlebell exercises [5], and put it all together with this basic beginner kettlebell workout [6].