Key Points

Seated leg curls produce greater overall hamstring hypertrophy compared to Nordic hamstring curls, particularly in the biceps femoris long head and semimembranosus muscles.
Nordic hamstring curls seem superior in targeting the sartorius and biceps femoris short head muscles.
Seated leg curls increase eccentric knee flexion torque, which is crucial for force absorption during high-impact activities like sprinting, potentially reducing hamstring injury risk.
A well-rounded hamstring training program should incorporate both seated and Nordic leg curls to maximize hypertrophy and minimize injury risk.

Introduction:

When it comes to building muscle and preventing injuries in the lower body, the hamstrings are a critical muscle group that demand attention in any training regimen. When it comes to isolating the hamstrings, one machine reigns supreme in the gym, the hamstring curl, usually performed in a seated or lying position. However, if this was the only hamstring isolation work you were doing, you are likely missing out on some gains.

Leg curls are especially effective at isolating the biceps femoris short head, a part of the hamstrings that isn't as heavily engaged during typical hinge patterns like Romanian deadlifts. Unlike the other heads of the hamstrings, the biceps femoris short head doesn't cross the hip joint, so it's not as activated in exercises that involve hip extension. Leg curls, however, specifically target knee flexion, which directly engages the biceps femoris short head, helping to develop this often underworked portion of the hamstrings. This isolation can lead to more balanced strength and hypertrophy across the entire hamstring group.

Recent research from Maeo et al. (2024) has highlighted the importance of training muscles at various lengths to maximize hypertrophy and minimize injury risk. Specifically, the study compared two hamstring isolation exercises: the Nordic hamstring curl, which is performed in a hip-extended position, and the seated leg curl, performed in a hip-flexed position. While both exercises target the hamstrings, they emphasize different aspects of the muscle group, leading to distinct outcomes in terms of hypertrophy and performance.

HYPERTROPHY FINDINGS

Seated Leg Curls

The seated hamstring curl is a machine-based exercise where the individual sits with their legs extended in front, securing their ankles under a padded lever. The movement involves curling the legs downward toward the body, emphasizing the hamstrings' contraction as they pull the weight while the hips remain flexed, keeping the muscles elongated throughout the exercise. The Maeo study found that eccentric-biased seated leg curls, which keep the hamstrings elongated throughout the exercise, led to greater overall hamstring hypertrophy compared to Nordic hamstring curls (1). This effect was particularly pronounced in the biceps femoris long head and semimembranosus muscles. The reason for this is pretty straightforward: muscles under high tension at longer lengths tend to experience more significant growth. This has been shown in Kubo (2019), Sato (2021), Pedrosa (2022), Kassiano (2023), and Maeso (2023) (2,3,4,5). All that is to say that, if you are looking to maximize your hamstring size, incorporating seated leg curls into your routine is all but mandatory.

Nordic Hamstring Curls

Another popular hamstring isolation movement is the Nordic hamstring curl. For those unfamiliar, the Nordic hamstring curl is an exercise where the athlete kneels on the ground with their feet secured, then slowly lowers their upper body forward while keeping the hips extended and torso straight. It is incredibly difficult to do unassisted and took me months of training before I was even able to do even a single unassisted rep. That said, in the Maeo (2024) study, Nordic hamstring curls were more effective in promoting growth in the sartorius and biceps femoris short head muscles of the hamstrings (1). This finding is intriguing as it suggests that while long muscle lengths are beneficial for overall hamstring development, shorter muscle lengths—achieved in the hip-extended position of Nordic curls—can effectively target other muscles within the group. This nuance highlights the importance of exercise variety in achieving balanced hypertrophy across all parts of the hamstrings.

INJURY PREVENTION

Maeo et al. (2024) reported that there was an increase in eccentric knee flexion torque observed in the seated leg curl group (1). This torque is crucial for force absorption during high-impact activities like sprinting. Stronger eccentric control could lead to better performance and a reduced risk of hamstring injuries. Additionally, the seated leg curl group saw more significant changes in the proximal aponeurosis of the biceps femoris long head—a critical area prone to injury.

An aponeurosis is a type of connective tissue that is similar to a tendon. It is a flat, broad sheet of fibrous tissue that connects muscles to the bones or to other muscles. Unlike tendons, which are more cord-like, aponeuroses are wider and spread out over a larger area. They serve as a strong, durable structure that allows for the transmission of force from muscle to the points of attachment, helping to stabilize and support muscles during movement. In the context of hamstrings, the aponeurosis plays a crucial role in connecting the muscle fibers to the skeletal system, particularly in areas prone to strain, like the biceps femoris long head. Strengthening the aponeurosis through targeted exercises can help reduce injury risk and improve muscle function. So, the expanded area and interface size of the aponeurosis suggest that seated leg curls might be more effective in strengthening this tendon-muscle connection, further reducing injury risk.

The study's findings on the seated leg curl’s impact on the proximal aponeurosis of the biceps femoris long head suggest that this exercise could be a key component in injury prevention strategies, especially for athletes prone to hamstring injuries (1). The increased aponeurosis area may lead to better force distribution across the muscle, reducing the risk of strain during high-intensity activities.

INTERPRETATION

The information from Maeo et al. suggests that the differences in hypertrophy and strength gains between the two exercises cannot be solely attributed to muscle length. Other factors, such as the type of load, exercise mechanics, and the presence of both eccentric and concentric phases, also play significant roles in driving adaptations. Thhis complexity suggests that when designing training programs, practitioners should consider multiple factors beyond just muscle length and hypertrophy.

While the study offers valuable insights, it also highlights areas where further research is needed. For example, the exact mechanisms behind the greater hypertrophy of the biceps femoris short head in Nordic curls remain unclear. Future studies could explore these mechanisms in more detail, potentially leading to more targeted exercise recommendations.

Moreover, while the study suggests that seated leg curls might reduce hamstring injury risk, this hypothesis needs to be tested in longitudinal studies tracking injury rates in athletes who incorporate these exercises into their training.

PRACTICAL APPLICATIONS

While seated leg curls are superior for overall hamstring hypertrophy, Nordic curls are superior for growing the biceps femoris part of the hamstring. Understanding these nuances allows for more strategic exercise programming, ensuring that all aspects of the hamstrings are effectively targeted. This variety ensures a well-rounded development of the hamstrings, catering to different aspects of muscle growth and strength.

When designing any training program, not just hamstrings, it’s important to recognize that different exercises will impact muscles differently, even within the same muscle group. Taking a multi-pronged approach will help ensure you aren’t leaving easy gains on the table. As such, varying exercises to stimulate hypertrophy across all relevant muscles while preventing overuse injuries. For athletes, particularly those involved in sports that require sprinting, incorporating seated leg curls could provide superior injury prevention by enhancing the strength and resilience of the hamstrings at longer muscle lengths.

Personally, I like to do 6 weeks of one type of hamstring curl before switching to another. When I hop back to previous varition, I usually will change rep range or vartiation. An example of this would be doing seated hamstring curls for 6 weeks at 12-15 reps, then doing Nordic curls for 6 weeks on my FreakAthlete for 8-10 reps, before doing seated hamstring curls again, but this time I might do 10-12 reps instead, or do a single leg variation.

CONCLUSION

This research highlights the importance of a nuanced approach to hamstring training. Both seated and Nordic leg curls offer unique benefits, making them valuable tools in a well-rounded training program. By understanding the nuances of how different exercises affect muscle hypertrophy and injury risk, practitioners can design more effective training regimens that maximize performance and minimize injury.

Incorporating both hip-flexed and hip-extended leg curls into a training routine ensures comprehensive hamstring development, leading to better performance and reduced injury risk. Whether you’re an athlete aiming to enhance your sprinting performance or a trainer seeking to optimize your clients' muscle growth and injury prevention, this research provides a solid foundation for informed exercise selection and programming.

Sources:

Maeo S, Balshaw TG, Nin DZ, Mc Dermott EJ, Osborne T, Cooper NB, et al. Hamstrings Hypertrophy is Specific to the Training Exercise: Nordic Hamstring versus Lengthened State Eccentric Training. Med Sci Sports Exerc. 2024 Jun 6.
Kubo K, Ikebukuro T, Yata H. Effects of squat training with different depths on lower limb muscle volumes. Eur J Appl Physiol. 2019 Sep;119(9):1933-1942.
Sato S, Yoshida R, Kiyono R, Yahata K, Yasaka K, Nunes JP, at al. Elbow Joint Angles in Elbow Flexor Unilateral Resistance Exercise Training Determine Its Effects on Muscle Strength and Thickness of Trained and Non-trained Arms. Front Physiol. 2021 Sep 16;12:734509.
Pedrosa GF, Lima FV, Schoenfeld BJ, Lacerda LT, Simões MG, Pereira MR, et al. Partial range of motion training elicits favorable improvements in muscular adaptations when carried out at long muscle lengths. Eur J Sport Sci. 2022 Aug;22(8):1250-1260.
Kassiano W, Costa B, Kunevaliki G, Soares D, Zacarias G, Manske I, et al. Greater Gastrocnemius Muscle Hypertrophy After Partial Range of Motion Training Performed at Long Muscle Lengths. J Strength Cond Res. 2023 Sep 1;37(9):1746-1753.
Maseo S. Effects of hip extension training performed with full versus partial range of motion at long muscle lengths on muscle hypertrophy and sprint performance. 27th Annual Congress of the ECSS. 06.07.2023.

DISCLAIMER

The information in this article is for educational and informational purposes only and is not intended as medical advice, diagnosis, or treatment. Always consult with a qualified healthcare provider or medical professional before beginning any new exercise, rehabilitation, or health program, especially if you have existing injuries or medical conditions. The assessments and training strategies discussed are general in nature and may not be appropriate for every individual. At Verro, we strive to provide personalized guidance based on each client’s unique needs and circumstances.