1.) Shorten Rest Periods.
Progressively shaving seconds off your rest period can help to raise your metabolism. Just don't go too low, warns Joe Stankowski, C.P.T., a trainer in Grand Rapids, Mich. "You need a minimum of 30 seconds' rest or you risk burning out," he says. The one exception: circuit training, which requires no rest between sets.
2.) Train the Whole Body.
If you've been following a split routine — upper-body exercises one day, lower body the next — condense both into one day. Your growth hormone levels will spike, and that burns fat.
3.) Alternate Sets.
Do a set of a lower-body exercise followed by an upper-body one, such as a squat and then a row. This way, one muscle group has time to recover while you train another one.
4.) Increase Lifting Speed.
You can more calories by doing explosive exercises like plyo pushups (where you push yourself into the air) and box jumps, or by using lighter weights and lifting them more explosively on the upward phase of the movement.
5.) Decrease Reps.
Most guys' workouts are based around the idea of 10 reps per set. But according to Jim Smith, C.S.C.S., a strength coach in Sayre, Pa., you'll get a much bigger spike in metabolism by reducing your reps and tacking on an additional set. Try sets of six to eight reps.