The hamstrings are a group of four muscles: semimembranosus, semitendinosus, biceps femoris short head, and biceps femoris long head. Understanding their anatomy is crucial for effective training. These muscles are divided into medial (semimembranosus and semitendinosus) and lateral (biceps femoris) compartments. The medial hamstrings originate from the ischial tuberosity (part of the pelvis) and insert into the medial side of the tibia (shin bone). The biceps femoris short head originates on the femur (thigh bone) and inserts into the fibular head (part of the lower leg). The biceps femoris long head originates on the ischial tuberosity and also inserts on the fibula.
The hamstrings are biarticular muscles, meaning they cross both the hip and knee joints. This allows them to contribute to both knee flexion (bending the knee) and hip extension (straightening the hip). However, the biceps femoris short head only crosses the knee joint, and therefore doesn’t contribute to hip extension.
While some argue that leg curls are superior to hip extension movements because all four hamstring muscles cross the knee joint, focusing on both knee flexion and hip extension exercises is recommended for optimal hamstring development. A recent study by Schoenfeld et al. found that lying leg curls exhibited higher activation in the distal hamstrings (closer to the knee), while straight leg deadlifts showed similar proximal hamstring activation (closer to the hip).
Considering the three mechanisms of hypertrophy—mechanical tension, metabolic stress, and muscle damage—it’s crucial to incorporate exercises that emphasize each mechanism. Lying leg curls may not maximize muscle damage due to the lack of hamstring stretch. Seated leg curls, on the other hand, provide a stretch at both the hip and knee, potentially leading to more muscle damage and stimulating hypertrophy.
Regarding ankle position during leg curls, both plantarflexion (pointing the toes down) and dorsiflexion (pointing the toes up) can be utilized. While dorsiflexion may allow for greater weight lifted due to assistance from the gastrocnemius (calf muscle), research suggests that EMG activation remains similar regardless of ankle position when controlling for load. Choosing the most comfortable ankle position is generally recommended.
A variety of leg curl variations exist, such as gliding leg curls and Nordic hamstring curls. The gliding leg curl combines knee flexion and hip extension, offering an efficient way to target the hamstrings. The Nordic hamstring curl, which involves lowering and raising the body using primarily hamstring strength, is particularly challenging and has shown promise for injury prevention.
Glute-ham raises are another effective exercise for hamstrings, combining knee flexion with isometric hip extension. While the torque curve differs from lying leg curls, the glute-ham raise requires significant hamstring strength and promotes active hip extension. Combining both exercises in a training program can provide a comprehensive hamstring stimulus.
For hip extension movements, the 45-degree hyperextension offers consistent torque throughout the range of motion. This is because the body never reaches a perpendicular position to the ground, maintaining tension on the hamstrings. Good mornings, Romanian deadlifts (RDLs), and stiff-legged deadlifts (SLDLs) also effectively target hip extension, and variations in stance width can be utilized to emphasize different hamstring muscles.
Contrary to popular belief, squats and deadlifts are not optimal hamstring exercises. While hamstrings contribute to stability during these movements, their length doesn’t change significantly, limiting their hypertrophic stimulus. Prioritizing targeted hamstring exercises is crucial for maximal growth.
The belief that hamstrings are predominantly fast-twitch muscles and therefore should be trained with low reps is not entirely accurate. Research indicates a relatively even distribution of type I and type II muscle fibers in the hamstrings. Training with a variety of rep ranges and intensities is recommended for optimal development.
Finally, strengthening the hamstrings is vital for injury prevention. Eccentrically accentuated exercises, such as good mornings and Nordic hamstring curls, can increase sarcomeres in series (making the muscle longer) and improve hamstring strength at longer muscle lengths, potentially reducing the risk of hamstring strains and other injuries.
