You can burn 8-10 calories per minute just by pumping iron.
Compare that to running or bicycling, where you burn 10-12 calories a minute, and that’s not too bad. But wait, it gets better.
Lifting weights gives you a metabolic spike which lasts for approximately an hour after your workout. This is due to the fact that your body is trying to help your muscles recover from the workout. During this spike, your body will continue to burn calories even though you have finished your strength training session … and even while you are relaxing. And, because muscles use a lot of energy to sustain themselves, for every 3 pounds of muscle you build, your body will burn an additional 120 calories per day.