Muscle damage and repeated-bout effect after a typical Nordic hamstring exercise session

The present study investigated muscle damage and repeated-bout effect after a typical Nordic hamstring exercise (NHE) session. Thirteen trained male adults were recruited. Muscle damage was monitored through eccentric strength, passive range of motion (ROM), muscle soreness, and muscle swelling. Assessments were performed at baseline and one (day-1), two (day-2), three (day-3), and four (day-4) days after 24 NHE repetitions. The procedures were replicated after four weeks to examine the repeated-bout effect. After the first bout, hamstring eccentric strength decreased up to day-3 [effect size (ES) range: -2.28/-1.95]. Passive ROM decreased up to day-4 (ES range: -1.62/-0.64), while muscle soreness increased on day-2 (ES=1.63) and day-3 (ES=1.53). No change in muscle swelling was observed. After the second bout, hamstring eccentric strength (ES=-1,20) decreased only on day-1. Passive ROM decreased up to day-3 (ES -0.85/-0.34). These changes were by a smaller magnitude compared to the first bout. The first NHE bout impaired hamstring strength and passive ROM, with muscle soreness also perceived, while the second bout reduced muscle damage symptoms and shortened the time to recovery. While recovery is needed when an NHE session is performed for the first time, following NHE sessions may scarcely interfere with the training routine.