Should you fail before you even really get started? At least two scientific studies say yes. In the first, published in the July 2015 issue of the European Journal of Applied Physiology, subjects performed one set of leg extensions, using 20 percent of their one-rep max (1RM) and repping to failure. They then did three sets of eight to 12 reps at 75 percent of their 1RM, a routine they repeated twice per week.
After eight weeks, the pre-exhaust group increased their 1RM, the cross-sectional area of their quadriceps, and their muscular endurance more so than the control group who just did the three sets of eight to 12. Research published in the January/February 2016 issue of The Journal of Sports Medicine and Physical Fitness backed those results, but at a higher weight. Subjects in that study did a pre-exhaust leg-extension set at 80 percent of 1RM to failure to lead off their twice-weekly workouts, which consisted of three sets of 15 to 20 reps at 50 percent of 1RM.
After eight weeks, those who added the additional pre-exhaust set experienced greater increases in one-rep strength, endurance, and work efficiency—although the quads did not grow more as a result. Still, though, a leadoff set to failure could give you a leg up in your training efforts.