Muscle failure is defined as the point during an exercise at which the muscle has fully fatigued and is unable to perform an additional repetition of the exercise in good form.
Most of the power lifters use this technique to increase strength. However, there were studies made by Australian researchers which discovered that doing more than one set to failure on bench press for eight weeks offered no additional increase in strength gains, and the reason may be that doing only one set to failure allows enough stimulus to be delivered to the muscle fibres without the risk of overtraining.
Obviously, this method should not be used for those who train alone in the gym – unless it’s done with machine-based exercises such as Smith machine squats. One should never attempt to do barbell presses, barbell squats or leg presses to failure. All these exercises require an adequate spotter to ensure that the last rep is done accurately and safely.
You may choose to perform just the last set of every exercise in your routine (except abdominals) to muscle failure as a boost to your workout over a period of eight weeks, just to manipulate the routine. Just ensure that you only perform on the last set of the exercise.