Muscle Damage and the Repeated-bout Effect After a Typical Nordic Hamstring Exercise Session

The present study investigated muscle damage and the repeated-bout effect after a typical Nordic hamstring exercise session. Thirteen trained male adults were recruited. Muscle damage was monitored through eccentric strength, passive range of motion, muscle soreness, and muscle swelling. Assessments were performed at baseline and 1 (day 1), 2 (day 2), 3 (day 3), and 4 (day 4) days after 24 Nordic hamstring exercise repetitions. The procedures were replicated after 4 weeks to examine the repeated-bout effect. After the first bout, the hamstring eccentric strength decreased up to day 3 (effect size range:-2.28/-1.95). The passive range of motion decreased up to day 4 (effect size range:-1.62/-0.64), while the muscle soreness increased on day 2 (effect size=1.63) and day 3 (effect size=1.53). No change in muscle swelling was observed. After the second bout, the hamstring eccentric strength (effect size=- 1.20) decreased only on day 1. The passive range of motion decreased up to day 3 (effect size=- 0.85/-0.34). These changes were by a smaller magnitude compared to the first bout. The first Nordic hamstring exercise bout impaired hamstring strength and passive range of motion, with muscle soreness also perceived, while the second bout reduced muscle damage symptoms and shortened the time to recovery. While recovery is needed when a Nordic hamstring exercise session is performed for the first time, following Nordic hamstring exercise sessions may scarcely interfere with the training routine.