Abstract Introduction: The Nordic Hamstring exercise (NHE) increases hamstring strength, but muscle soreness and excessive fatigue may hinder adoption. The assisted NHE (A-NHE), with an elastic band around the chest lowering the force in the eccentric lowering phase, may be a less demanding alternative. We investigated the effectiveness of A-NHE versus NHE on hamstring strength, muscle soreness, and perceived exertion. Methods: We randomized 31 youth elite football players (under-14 and -15) from a single professional football academy to either NHE or A-NHE, who performed the same supervised 8-week program. The A-NHE was performed with an elastic band, progressing from heavy to light assistance. A blinded tester assessed Nordic hamstring strength, while hamstring muscle soreness and perceived exertion were assessed during each session. Results: Intention-to-treat analysis showed no group by time interaction (p = 0.61) for Nordic hamstring strength. Both groups improved significantly (A-NHE mean difference: 3.7 kg, 95% CI [2.1; 5.3]; NHE mean difference: 3.2 kg, 95% CI [1.2; 5.2]) corresponding to approximately 20%. The NHE group reported significantly higher hamstring muscle soreness (beta = 1.77, p < 0.01) and perceived exertion (beta = 1.54, p < 0.01). Conclusion: Eight weeks of assisted-versus regular Nordic Hamstring training led to similar strength gains, but with lower hamstring muscle soreness and perceived exertion. Highlights In this randomized controlled trial, we compare, for the first time, the assisted and non-assisted Nordic Hamstring Exercise. In youth elite footballers, we analyzed Nordic Hamstring strength, hamstring muscle soreness, and rating of perceived exertion across 8 weeks. No between-group difference in Nordic Hamstring strength was observed, with each group increasing strength by ~20 %. The assisted Nordic Hamstring group reported lower hamstring muscle soreness and rating of perceived exertion. These findings may improve adoption and compliance rates in settings where fear of muscle soreness and excessive fatigue are dominant barriers.
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