Performing a low-resistance set to failure (20 percent of your one-repetition maximum, or 1RM) before doing traditional weight training for a muscle group results in greater muscle hypertrophy— according to Brazilian researchers. Young men trained for eight weeks on a knee-extension machine. The program consisted of three sets of eight to 12 repetitions at 75 percent of 1RM. Before each workout, one pre-exhaustion group did a single set of knee extensions to exhaustion using light weights. The pre-exhaustion group gained more muscle mass, strength and muscle endurance than the group training with traditional methods. It is unclear whether this technique works with more experienced weight trainers practicing multi-joint exercises.
Source: European Journal of Applied Physiology, published online March 10, 2015; Annals of Internal Medicine, 162: 326-334, 2015