What's not to love about circuit training? Combining heart-pumping elements of cardio with strength-training moves means you torch calories while toning muscles. It's just so efficient.
Here's a fun yet challenging circuit workout from Equinox trainer Lauren Fairbanks. Have a stopwatch handy for this one since you perform each exercise for 60 seconds. Don't be daunted by the time - you can do anything for a minute. Plus, it's nice to have the luxury of not needing to count all those reps.