1. Partial Reps:
do reps over only a partial range of motion - at the top, in the middle or at the bottom - of a movement. best options: power-rack bench press and smith-machine upright row.
2. Drop Sets:
after completing your reps in a heavy set, quickly strip an equal amount of weight from each side of the bar or select lighter dumbbells and continue repping until you fail. then strip off more weight to complete even more reps. best option: any selectorized machine, such as the let extension or leg curl, as well as cables and all dumbbell moves in which going from one weight to the next is seamless.
resist the downward motion of a very heavy weight. for example, on the barbell curl, use a weight that's 15-25% heavier than you can typically handle and fight the negative as you slowly lower the bar to the start position. have your partner assist with the positive portion of the rep. best options: smith-machine decline press and bench press.
4. Forced Reps:
have a training partner assist you with reps at the end of the set to help you work past initial failure. your training partner should help lift the bar with only the force necessary for you to keep moving and get past the sticking point, no more than that. best option: preacher curls and barbell curl. the best exercises for forced reps allow your workout partner the most leverage to help you through those post-failure reps.
take brief rest periods during a set of a given exercise to squeeze out more reps. use a heavy weight you can lift 2-3 reps, rest up to 20 seconds, then try for another 2-3 reps. rest again briefly, then try for as many reps as you can handle and repeat once more. best option: plate-loaded leg press and T-bar row.
Source: Failing to Grow, by: Jimmy Pena, MS, CSCS
REPS Magazine ~ Winter 2010