Next time you go to the gym, instead of doing your regular reps, just stop in the middle of the first one and hold it as long as you can. Seriously, just get in the position and hold it. Imagine a bench press where you push the weight up off your chest and hold it halfway up. Just hold it in a curl. Hold it in a shoulder press. Hold the squat. You'll hate it for a while, but it'll tear you up. You can actually go into the gym and never move. It's unbelievable how much you sweat.