In healthy young men, two types of hamstring exercises—lengthened state eccentric training and Nordic hamstring training—each increase isometric knee flexion strength by about 25-27%, and neither...
Mechanism
Synthesis from 1 study
Both training methods make the back of the thigh stronger, but they do it in different ways: one stretches the muscles while they contract to grow the big muscles that cross two joints, and the other focuses the work on smaller muscles that only bend the knee. Both end up making the knee just as...
Most probable mechanism
When the hamstrings are stretched while being forced to contract backward, the muscle fibers and their connecting tissue grow thicker and stronger, making the leg more powerful when bending the knee while standing still.
Hip flexion during eccentric knee flexion elongates the biarticular hamstring muscles across both hip and knee joints, placing them under high mechanical tension.
High mechanical tension during lengthened-state eccentric contractions activates mechanotransduction pathways that increase muscle protein synthesis and reduce protein breakdown.
Increased protein synthesis leads to addition of sarcomeres in series and radial growth, resulting in greater muscle volume in the biceps femoris long head and semimembranosus.
Eccentric forces transmitted through the biceps femoris long head aponeurosis stimulate fibroblast activity, increasing collagen synthesis and expanding aponeurosis area and width.
Larger muscle volume and expanded aponeurosis improve force transmission efficiency and reduce strain concentration, enhancing maximum isometric knee flexion torque.
Less supported by current evidence, but not ruled out
When the body leans forward and lowers itself using the back of the thighs, the knee-bending muscles that don't cross the hip grow larger, increasing the force the knee can produce when held still.
Hip extension during Nordic hamstring training limits stretch on biarticular hamstrings, reducing their mechanical contribution.
Reduced biarticular hamstring activation increases relative recruitment of monoarticular knee flexors, including the short head of the biceps femoris and semitendinosus.
Eccentric loading of monoarticular knee flexors stimulates localized muscle protein synthesis and hypertrophy in these muscles.
Increased volume of monoarticular knee flexors enhances force production during isometric knee flexion.
Evidence from Studies
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Contradicting (1)
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Hamstrings Hypertrophy Is Specific to the Training Exercise: Nordic Hamstring versus Lengthened State Eccentric Training
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