Background:
Hamstring strengthening exercises are often used for injury prevention, rehabilitation and performance enhancement. Knowledge about muscle forces, muscle activation, and fascicle behavior during these exercises can help optimize exercise prescription, but information on these outcomes across different exercises is lacking.

Objective:
The aim of this study is to characterize and compare lower-limb joint moments, muscle activation, and biceps femoris muscle fascicle behaviour between three hamstrings exercises: the Nordic hamstring exercise (NHE), the single-leg Roman chair (RCH), and the single-leg deadlift (DL).

Design:
Ten male participants performed the NHE, RCH and DL in a randomized order with a 1RM load, while full-body kinematics, ground reaction forces, lower-limb muscle activation and biceps femoris muscle fascicle behaviour were measured. Joint moments were determined using a musculoskeletal model.

Results:
Biceps femoris fascicles initially shortened and remained quasi-isometric before actively lengthening during the NHE and RCH, while they lengthened and subsequently shortened in the DL. The increase in fascicle length was largest in the NHC (30.83 ± 11.74 mm), followed by the DL and RCH (18.52 ± 5.2 and 17.75 ± 7.87 mm, respectively), with no significant difference between the DL and RCH. Mean fascicle length was largest in the DL, followed by the RCH and NHC, with all pairwise comparisons being significant. Peak knee joint moments were highest for the NHE, followed by the RCH and DL (6.62 ± 1.21, 3.80 ± 1.28, 1.04 ± 0.44 N·m/kg, respectively). Peak hip joint moments and peak muscle activation did not significantly differ between the exercises.

Conclusion:
Biceps femoris fascicle lengthening and peek knee joint moments were largest during the NHE. Peak hip joint moments and muscle activation did not differ between the exercises. These findings can be used to optimize exercise prescription and target specific adaptations to maximize the effectiveness of training.