Purpose:
Hamstring strain injuries (HSIs) are highly prevalent in sports. While the Nordic Hamstring Exercise (NHE) is used for prevention, and the Askling L-Protocol is employed for rehabilitation, their evidence has been examined in isolation.

Methods:
This systematic review evaluates and contrasts these protocols to clarify their distinct roles. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines (PROSPERO: CRD420251128030), a systematic search of four databases identified randomised controlled trials (RCT) and quasi-experimental studies (2010–2025) in athletic populations. The risk of bias was assessed using Cochrane Risk-of-Bias 2 (RoB 2) tool and the Risk of Bias in Non-Randomised Studies of Interventions (ROBINS-I) tools, and results were narratively synthesised.

Results:
Twenty-five studies involving 2,613 athletes were included. For prevention, a large cluster-RCT reported a substantial reduction in acute HSI incidence following an NHE programme [adjusted risk ratio (RR) = 0.293, 95% confidence interval (CI) 0.150–0.572], and a 10-week NHE trial reported a large gain in peak eccentric hamstring strength (ECC-PHS +62.3 N; p = 0.006; Cohen’s d = 0.92). For rehabilitation, two Askling trials reported shorter mean return-to-sport time with the L-Protocol than with conventional programmes (mean differences 23 and 37 days; p < 0.001 in both trials; 95% CIs not reported)

Conclusions:
Evidence from the included trials suggests that the NHE-based programmes can support prevention strategies, with several studies reporting improvements in eccentric strength and muscle architecture, and that the Askling L-Protocol is supported primarily by rehabilitation trials reporting shorter return-to-sport times. Overall, these findings indicate that the two protocols may serve different clinical purposes and should be selected according to the athlete’s stage on the injury continuum.