Should Do About It)
When it comes to lower-body development, the quadriceps almost always steal the spotlight. This imbalance is prominent both in scientific literature and in the daily routines of commercial gyms across the world. For most lifters, lower-body workouts are heavily saturated with movements like squats, leg presses, and lunges. These multi-joint compound exercises hammer the quads whether an athlete intends them to or not, providing a massive baseline of automatic volume.
The hamstrings, on the other hand, rarely enjoy that same level of accidental stimulus. Unless an individual is deliberately programming dedicated leg curls and hip hinges into their routine, the posterior thigh muscles easily end up as an afterthought.
In the realm of scientific research, the quads also tend to simply be much easier to study. Most human beings store less subcutaneous fat on top of their quadriceps, and the individual heads of the quad muscle group are significantly more accessible for imaging via ultrasound technology because they consistently lie closer to the skin than the deeper, more complex architecture of the hamstrings.
However, a wealth of valuable research on hamstring training exists—much of it courtesy of strength and conditioning professionals who have long sought to mitigate lower-limb injuries. Given how prevalent and debilitating hamstring strains are in athletic populations, targeted hamstring training—specifically movements like Nordic curls—has received intense academic and practical attention as a vital intervention to reduce strain injury risk.
To understand how to optimize posterior chain development, it helps to start with a quick review of functional anatomy. The hamstrings are comprised of four distinct heads: the biceps femoris long head, the biceps femoris short head, the semitendinosus, and the semimembranosus. All four heads share the primary function of flexing the knee joint, an action mirrored in any standard leg curl exercise. Furthermore, with the exception of the short head of the biceps femoris, the remaining three heads cross the hip joint and actively assist in extending the hips.
Why Squats and Leg Presses Fail to Build the Hamstrings
As one might intuitively deduce from this anatomical layout, comprehensive hamstring exercise selection requires two distinct classes of movements: leg curls and hip hinges. Yet, a common misconception in strength training is that heavy compound movements like squats and leg presses are also exceptional tools for building the hamstrings. Contemporary biomechanical research suggests otherwise.
This limitation was illustrated clearly in a pair of recent studies investigating muscle hypertrophy. The first study directly compared the barbell hip thrust to the traditional barbell squat, finding that neither movement produced substantial growth in the hamstrings. A second study compared a standard squat performed to 90 degrees of knee flexion against a deeper squat variation taken to 140 degrees of knee flexion. Once again, neither squat variation resulted in meaningful hamstring hypertrophy.
The root of this phenomenon lies in the biarticular nature of the hamstrings. In any exercise that requires an athlete to extend the knees and hips simultaneously—such as the squat—the hamstrings act as a double-edged sword. While they contract to help extend the hips, they simultaneously generate biomechanical torque that attempts to flex the knees, directly resisting the force of the quadriceps.
To circumvent this internal mechanical conflict and maximize movement efficiency, the central nervous system typically recruits alternative muscles that do not present this dual-action complication, most notably the gluteus maximus and the adductor magnus. Consequently, compound movements that demand a high degree of simultaneous torque for both knee and hip extension are fundamentally inefficient for driving significant hamstring growth.
Instead, for hip hinges to effectively stimulate the hamstrings, the knee joint must remain relatively fixed throughout the movement, keeping the demands placed on knee extension minimal. Interestingly, even within dedicated hip hinge and curl variations, localized hypertrophy patterns can differ widely across the individual heads of the muscle group.
Comparing Hip Hinges and Leg Curls
Recent investigations have begun mapping out how different movements preferentially load the complex architecture of the posterior chain. For instance, a study led by Kawama and colleagues examined the effects of varying training frequencies using an eccentric-only, lengthened partial stiff-legged deadlift exercise. The results showed that the long head of the biceps femoris, the semimembranosus, and the semitendinosus experienced substantial growth, whereas the short head of the biceps femoris showed comparatively minimal development.
Other researchers have directly compared hip hinge variants against leg curl variants. A notable study by Bourne and colleagues contrasted the 45-degree back extension with the Nordic hamstring curl. The long head of the biceps femoris and the semimembranosus grew more effectively from the 45-degree back extension, whereas the short head of the biceps femoris and the semitendinosus displayed superior growth from the Nordic hamstring curl.
Similarly, a recent study by Morin and colleagues compared the Nordic hamstring curl directly to the stiff-legged deadlift. The Nordic hamstring curl resulted in greater hypertrophy of the semitendinosus compared to the deadlift, while the stiff-legged deadlift produced greater growth in the semimembranosus. Both movements yielded similar gains in the long head of the biceps femoris, though the researchers did not measure changes in the short head.
Taken together, these studies indicate that hip hinges are generally superior for developing the long head of the biceps femoris and the semimembranosus, while leg curls tend to be more effective for targeting the short head and the semitendinosus. Beyond functional anatomy, this distinction provides a compelling rationale for including both movement categories in a well-rounded hypertrophy program.
Optimizing Leg Curl Variations
When it comes to selecting the most effective leg curl variant, work by Maeo and research colleagues offers valuable guidance. Their initial study compared seated leg curls to lying leg curls. A seated leg curl inherently flexes the hips, placing a greater passive stretch on the biarticular hamstrings than a lying leg curl. Conversely, the sartorius—a knee flexor that also assists in hip flexion—is placed in a more stretched position during the lying leg curl.
The findings revealed that the seated leg curl produced greater hypertrophy of the biarticular hamstrings, while the lying leg curl led to greater growth in the sartorius.
A subsequent study by the same research group compared the seated leg curl—performed with an intentional forward lean to maximize the stretch—against the Nordic hamstring curl. While the seated leg curl emphasizes a deep stretch for the biarticular hamstrings, the Nordic curl emphasizes eccentric resistance in the stretched position, becoming progressively more difficult as the body lowers toward the floor.
The Nordic curl resulted in greater growth of the short head and the sartorius, whereas the seated leg curl drove superior development in the long head and the semimembranosus. Growth of the semitendinosus, gracilis, and popliteus remained similar between the two groups.
Combined, these trials suggest that the seated leg curl is arguably the most effective single choice for overall hamstring hypertrophy. However, the lying leg curl retains value for targeting the sartorius, and the Nordic curl provides unique benefits for the short head of the biceps femoris. It is worth noting that these comparisons evaluated curl variations in isolation; pairing them with appropriate hip hinges in a comprehensive regimen may yield even more balanced results.
Exploring Advanced Technique Adjustments
Beyond baseline exercise selection, other academic inquiries offer intriguing insights into technique adjustments. One conference abstract by Maeo et al. compared half-reps performed exclusively in the stretched position against a full range of motion on a multi-hip machine. The study observed that growth of both the hamstrings and the glutes was generally greater when utilizing the lengthened partial technique, suggesting that experimenting with partial repetitions in the stretched position could be a viable strategy for lifters seeking additional growth.
In another study, Cadeo and colleagues investigated whether altering ankle position during lying leg curls could shift muscular emphasis. By having participants perform curls with their ankles fully plantarflexed or dorsiflexed, the researchers manipulated the length of the gastrocnemius—a calf muscle that also crosses the knee joint to assist in knee flexion—to see if more or less work could be shifted to the hamstrings. The results showed that ankle position had no meaningful impact on the hypertrophy observed in the long head of the biceps femoris, indicating that ankle placement during leg curls is primarily a matter of personal comfort and preference.
Ultimately, maximizing hamstring development requires a thoughtful combination of both hip hinges and leg curls. While hip hinges tend to bias the long head and the semimembranosus, dedicated leg curls are necessary to effectively target the semitendinosus and the short head. Among the available curl options, the seated leg curl stands out as the most broadly effective movement, supplemented by the unique mechanical advantages of lying curls and Nordic variations.
