Background: Stretching may promote detrimental effects on power output and maximal strength, but its direct effect on strength endurance remains unclear, as well as the influence of stretching duration. Objective: We aimed to evaluate the direct effect of static stretching of the quadriceps muscle, as well as the stretching duration, on the strength endurance during a unilateral knee extension exercise. Methods: Fifteen strength-trained men (age 28 ± 3 years, height 1.70 ± 0.09 m, body mass 70 ± 5 kg, training experience 5 ± 1 years) took part in a randomized counterbalanced cross-over study. Participants' total number of repetitions was assessed during strength endurance tests (four sets until failure at 70% of one-repetition maximum) performed under three different conditions in separate days: control - no stretching (CON), short-duration stretching (SDS) and long-duration stretching (LDS). Three stretching exercises, with 3 sets lasting 30 seconds each, were performed during SDS, while the number of sets during LDS was doubled. Data were analyzed using mixed models and magnitude-based inferences (MBI). Results: Despite of a significant decrease in the number of repetitions during the strength endurance test performed across the exercise sets (main Set effect p < .001), neither the number of repetitions in each set (main Condition effect p = .95) nor the total number of repetitions (main Condition effect p = .86) were significantly different between the conditions. MBI analysis revealed that changes in the total number of repetitions after SDS and LDS were mainly trivial compared to CON. Conclusions: Regardless of its duration, an acute session of static stretching did not influence strength endurance.
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