Failure training is a popular technique for maximizing muscle protein synthesis and muscle size. Failure training is not necessary for optimal adaptations to weight training— according to John Sampson and colleagues from the University of Wollongong in Australia. They compared training responses to failure, non-failure rapid shortening, and non-failure stretch shortening using the elbow flexors (biceps) during a 12-week program. All of the groups experienced improvements in strength, one-repetition maximum curl, muscle size and muscle activation. However, there were no differences between training methods. This was a small study involving recreationally active students, so the results are difficult to generalize to strength athletes.
Source: Scandinavian Journal Medicine & Science in Sports, published online March 24, 2015