Last month, I talked about temporary muscle failure. To recap—TMF is the point at which you absolutely cannot complete one last rep. While many people choose to employ this technique, it isn't necessary. As long as your last few reps are difficult, you're golden. That said, training to failure can make a difference if you need to push through a plateau. And if you've mastered that method, you may even want to consider pushing beyond failure—but it's a difficult way to train because it puts an immense amount of pressure on the body. You must, must, must use proper form at all times in order to avoid injury. And just like training to TMF, you should never push a muscle group beyond failure more than once a week.
In fact, I only recommend you fail harder if you are completely familiar with the rules and regulations of training to failure. And if you are, I'd recommend you try the following:
1) FORCED REPETITIONS: If you are training with a partner, you can enlist their help to push past the point at which you can't move the weight anymore. Or, if you're doing single-arm moves, assist your working arm with your resting hand. Either way, you may be able to squeeze out one or two more reps.
2) PARTIAL REPETITIONS: If you can't complete another full rep, try lifting the weight through one or two partial repetitions. For example, if you're lifting a barbell for bicep curls, lift until your arms are bent at 90 degrees. Lower and repeat a few more times if possible.
3) DROP SETS: Quite possibly the easiest way to push beyond TMF. When your muscles fail, change your weight to something lighter and complete full repetitions until your muscles fail again. Lighten the weight again, or just call it quits. Note that cable machines make this technique super easy to do.
Remember, training to temporary muscle failure requires that you closely observe your form every second that you are lifting. And again, never use these techniques more than once a week per muscle group. I know I sound like a tape deck on repeat with this one—but good form means less injuries.