More Refreshing Than: High-Intensity Interval Training (HIIT)
The idea behind this type of lifting is that building muscles requires pushing them to failure, says Adam Zickerman, ACSM, author of Power of 10: The Once-A-Week Slow Motion Fitness Revolution and owner of InForm Fitness gyms. He doesn't mean just "feel the burn"; he wants you to go one rep beyond what you ever thought you could do. Zickerman's head-to-toe program involves six exercises: adduction squeezes (for the hips), chest presses, lat pull-downs and lateral raises or overhead presses (for the shoulders).
DIY and Stay Cool: For chest presses, you'll push the weight up for 10 seconds, then down for 10 seconds, without locking your elbows at the top or resting at the bottom. Each set of three to five reps (whatever it takes for you to feel like you absolutely can't do another) will take about 90 seconds, Zickerman says. Completing all six exercises shouldn't take longer than 20 minutes—so as soon as you break a sweat, you're done.