Keese, F, Farinatti, P, Massaferri, R, Matos-Santos, L, Silva, N, and Monteiro, W. Acute effect of proprioceptive neuromuscular facilitation stretching on the number of repetitions performed during a multiple set resistance exercise protocol. J Strength Cond Res 27(11): 3028–3032, 2013—It has been proposed that fatigue during strength exercise is negatively influenced by prior proprioceptive neuromuscular facilitation (PNF) stretching. However, it is possible that the effects of PNF on muscle endurance are affected by stretching duration. This study investigated the influence of PNF on the number of repetitions of the leg curl exercise performed with multiple sets and submaximal load. Nineteen men (age 25 ± 1 years, weight 75.8 ± 4.2 kg, height 178.1 ± 3.8 cm, 10-repetition maximum [RM] 78.3 ± 6.9 kg) performed 4 sets of leg curl with 10RM load with and without previous PNF (3 sets of hip flexion either with knees extended or flexed, duration ∼2.5 minutes). The total number of repetitions decreased along sets in both situations (38.6% in control and 41.0% in PNF sessions, p < 0.001). However, no difference between control and PNF was detected for the number of repetitions in each set (first set, p = 0.330; second set, p = 0.072; third set, p = 0.061; fourth set, p = 0.150). In conclusion, the number of repetitions performed in multiple sets of the leg curl was not decreased by prior PNF stretching. Therefore, it appears that a moderate level of PNF could be used before resistance exercise with a minimal negative effect.