First, the Romanian deadlift has been considered one of the best deadlift variations for hypertrophy emphasis. High prolonged stretch, allowing for maximized eccentric tension & increased amounts of fiber damage & repair. RDLs work the hamstrings longer lengths, which research suggests leads to superior hypertrophy compared to exercises that only contract the muscle at shorter lengths. Heavy loads allow for increased mechanical tension which is needed for hypertrophy. 

Supporting studies for RDL: 

This suggests that variations like the Step-RD, which increase the range of motion, can enhance posterior chain muscle excitation. pmc.ncbi.nlm.nih.gov

This study emphasizes the RDL's effectiveness in targeting the hamstring muscles over the lower back muscles. pmc.ncbi.nlm.nih.gov

This underscores the RDL's focus on hamstring engagement, making it a suitable exercise for hamstring hypertrophy. researchgate.net

Let’s talk a little bit about SLDLs & what their role is in your training program. They emphasize the hamstring complex, increasing the stretch under load. This creates high mechanical tension and stretch-mediated hypertrophy, key drivers of muscle growth. Training the hamstring in the stretched position & its correlation to hypertrophy has been shown to lead to greater muscle growth. pmc.ncbi.nlm.nih.gov

Not only are SLDLs great for hypertrophy, they can enhance posterior chain strength, & increase flexibility by promoting greater hamstring mobility under load.

Let’s talk a little bit about what muscles are directly being engaged: (minimal knee flexion, hip extension emphasis)

Posterior chain

• Hamstrings (Biceps Femoris, Semitendinosus, Semimembranosus) – These muscles are heavily engaged due to the minimal knee bend, emphasizing stretch and contraction.
• Gluteus Maximus – Acts as a primary hip extensor, especially at the top of the movement.
• Erector Spinae – Stabilizes the spine and maintains a neutral back throughout the lift.
• Adductors – Assist in hip stability and extension.
• Core Muscles – Engage for bracing and spinal support during the lift.

SLDLs heavily target the semitendinosus muscle within the hamstring complex. This is because the semitendinosus is more active during hip-dominant movements that emphasize a lengthened muscle position, such as the SLDL/RDL. However, the biceps femoris (long head) and semimembranosus are also significantly recruited, especially during hip extension at the top of the movement.

Extensive research has shown SLDLs to be a top tier exercise for hamstring growth, specifically due to the high mechanical tension & stretch-mediated growth. In comparison to squats, other deadlift variants, hip thrusts, good mornings, & other alternative exercises, the stiff leg deadlift still holds the crown for best hamstring concentrated stimulation & activation. Individual goals & biomechanics do however play a role! If you want to grow your hamstrings &/or increase strength/force production, I 100% recommend adding SLDLs into your regimen. 

Research has shown that hamstring curls or single joint movements can provide the best activation & correlation to muscle growth, which is due to the mechanics & stretch-mediated hypertrophy. 

Article supporting training the StiffLeg dead lifts & their enhanced growth: https://www.bodybuilding.com/content/a-scientific-approach-to-hamstring-training.html?utm_source=chatgpt.com

Also supports single joint movements for size. 

Article supporting the effective engagement of the hamstrings while using SLDLs: pmc.ncbi.nlm.nih.gov

Article about SLDLs positioning the hamstrings in a stretched state throughout the exercise, potentially enhancing muscle growth by leveraging this length-tension relationship: pmc.ncbi.nlm.nih.gov

Nordic curl variations are known for being highly beneficial due to their ability to emphasize eccentric overloading. Increased activation & lengthened position training can all improve muscular hypertrophy in the hamstrings. The Nordic curl is one of the most eccentrically demanding hamstring exercises, meaning the muscle lengthens under high tension.

Although Nordic’s are a great addition to a training regimen, they should not be solely relied on for hamstring hypertrophy. Nordic Hamstring Exercise can induce hypertrophy, particularly in the semitendinosus muscle, its overall effectiveness may be limited compared to other exercises that emphasize lengthened state eccentric training.

Studies supporting the Nordic curls: 

This study suggests that exercises emphasizing muscle lengthening under tension may induce more substantial hypertrophic adaptations. pubmed.ncbi.nlm.nih.gov

This study shows Nordic hamstring exercise favored hypertrophy of the ST muscle (21%) compared to the semimembranosus (SM, 5%) and BFlh (6%). onlinelibrary.wiley.com

Research involving resistance-untrained individuals assessed the impact of NHE and Stiff-Leg Deadlifts (SDL) on hamstring hypertrophy and strength transfer. Both exercises resulted in significant hypertrophy, with NHE showing a 24.3% increase in semitendinosus (ST) muscle volume. medrxiv.org

Seated hamstring curls can be considered a great exercise for hamstring complex hypertrophy. They should not be integrated into a training program alone, especially for well rounded growth. Seated hamstring curls do lengthen the hamstrings more than lying curls, making them superior for overall hamstring complex hypertrophy. Many movements listed above are hip hinge dominant, whereas the seated curl is focused on (single joint) knee flexion, ensuring balanced development when adding into a training program. Ability to progressive overload, implement constant tension @ high loads, increase mechanical tension, increase tension during the lengthening phase, boost hamstring activation, concentrated tension. But like I said above, they should not be relied on for well rounded development due to the lack of hip hinge movements. 

Studies supporting seated curls:

The findings indicated that hamstring muscle size increased more effectively with seated leg curl training, suggesting that training at longer muscle lengths promotes greater muscle hypertrophy.pubmed.ncbi.nlm.nih.gov

The results showed that hamstring hypertrophy was greater following seated leg curl training, with a 14.1% increase compared to a 9.3% increase in the prone leg curl group. This underscores the efficacy of seated leg curls in promoting muscle growth. sci-sport.com