Razor hamstring curl and Nordic hamstring exercise architectural adaptations: Impact of exercise selection and intensity

Objectives To investigate knee flexor strength and biceps femoris long head (BFlh) architectural adaptations following two different Nordic hamstring exercise (NHE) interventions and one razor hamstring curl (RHC) intervention. Methods Thirty recreationally active males performed a total of 128 reps of NHE bodyweight (n = 10), NHE weighted (n = 10), or RHC weighted training (n = 10) across 6 weeks. Following the intervention, participants avoided any eccentric training for 4 weeks (detraining period). Strength results during the NHE and RHC were recorded pre‐ and post‐intervention, as well as following detraining. Architectural characteristics of the BFlh were assessed weekly throughout the intervention and detraining periods. Results For the NHE weighted group, NHE strength increased (+81N, P = 0.044, d = 0.90) and BFlh fascicles lengthened (+1.57 cm, P < 0.001, d = 1.41) after 6 weeks of training. After 1 week of detraining, BFlh fascicle lengths shortened, with the largest reductions seen in the NHE weighted group (−0.96 cm, P = 0.021, d = −0.90). Comparatively, BFlh fascicle length and NHE strength responses were moderate in the NHE bodyweight group and negligible in the RHC weighted group. The greatest RHC strength changes (+82N, P = 0.038, d = 1.15) were seen in the RHC weighted group. Conclusions NHE weighted interventions induce large BFlh fascicle lengthening responses and these adaptations decay after just 1 week of detraining. NHE bodyweight training has a moderate impact on BFlh architecture while the RHC weighted group has the least. Weighted NHE and RHC training promoted exercise‐specific increases in strength. These findings suggest that exercise selection and intensity should be considered when prescribing exercises aiming to increase eccentric strength and BFlh fascicle length.