After nine weeks of Nordic hamstring exercises, recreationally active men showed a 17% increase in knee flexor strength, with noticeable improvements starting at three weeks, indicating a gradual...

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Against

Mechanism

Synthesis from 1 study

How it works

Your brain first learns to make your hamstring muscles fire more strongly and efficiently, giving you quick strength gains. After a few weeks, the muscles themselves change shape and become better at staying active during movement, which lets you produce even more force over time.

Most probable mechanism

In Simple Terms

At first, the brain learns to send stronger signals to the hamstring muscles, making the existing muscle fibers fire faster and more often. After a few weeks, the muscles start to change physically, allowing more powerful muscle fibers to be turned on only when needed, and those fibers stay active longer during relaxation, which helps produce more force over time.

Causal chain

High eccentric loading of the biceps femoris long-head during knee flexion increases sensory feedback from muscle spindles and Golgi tendon organs, enhancing excitatory input to spinal motor neurons.

Verified by multiple studies

which leads to

Spinal motor neurons increase their firing rate, delivering more frequent signals to muscle fibers, which elevates force production through rate coding before structural changes occur.

Verified by multiple studies

which leads to

Chronic mechanical stress raises the torque threshold required to activate additional motor units, favoring recruitment of higher-force, higher-threshold units during maximal efforts.

Verified by multiple studies

which leads to

Structural adaptations in muscle architecture, including increased fascicle length and sarcomerogenesis, alter length-tension relationships and enhance afferent feedback during relaxation.

Verified by multiple studies

which leads to

Altered spindle sensitivity and reduced spinal inhibition prolong motor unit activity during torque decline, increasing time-integrated force output during eccentric control.

Verified by multiple studies

Evidence from Studies

Supporting (1)

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Biceps femoris long-head motor unit discharge rates and recruitment thresholds vary across 9 weeks of eccentric training

Cohort Study

Human

2026 Apr 27

Contradicting (0)

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No contradicting evidence found

Gold Standard Evidence Needed

According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.

Source Study

Biceps femoris long-head motor unit discharge rates and recruitment thresholds vary across 9 weeks of eccentric training

Score: 31

DOI: 10.1016/j.jshs.2026.101142

Similar Assertions

Performing Nordic hamstring exercises over several weeks leads to a measurable increase in the amount of force needed to activate muscle motor units, with greater increases seen after longer training periods.

80%

Doing two different hamstring exercises—Nordic curls and stiff-leg deadlifts—makes you stronger at both, even if your muscles don’t grow the same way, meaning muscle growth isn’t what’s making you stronger in the other exercise.

79%

After nine weeks of Nordic hamstring training, the nervous system activates muscle fibers at higher force levels, and the firing rate of those fibers returns to normal, suggesting that muscle structure changes become more important than nervous system changes for gaining strength.

77%

When guys get stronger from doing isometric leg exercises, their hamstring muscles don’t start working differently alongside their quads—so the way their hamstrings fire doesn’t predict whether they’ll get stronger or not.

75%

After nine weeks of Nordic hamstring exercises, the force required to stop muscle fibers from firing increases by 12%, but no change is seen after three weeks, suggesting that the nervous system's control of muscle activation adapts slowly over time.

74%