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Strong Support

mechanistic

History

Performing Nordic hamstring exercises for three weeks leads to a 6% increase in the rate at which nerve signals activate the biceps femoris muscle, but this increase stops after nine weeks,...

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Against

Mechanism

Synthesis from 1 study

How it works

At first, your nerves fire more to make your hamstring stronger. After a few weeks, your nerves stop firing faster, but your muscle fibers grow longer and better at handling stretch, so it keeps getting stronger without needing more nerve signals.

Most probable mechanism

In Simple Terms

When you first start doing Nordic hamstring exercises, your nerves send stronger and more frequent signals to your hamstring muscle, making it contract harder right away. After a few weeks, the nerves stop sending even more signals, but the muscle itself starts to change physically — it gets longer and more resilient — so it can still produce more force without needing extra nerve input.

Causal chain

High eccentric loads during hamstring contractions activate muscle spindles, increasing sensory feedback to the spinal cord.

Verified by multiple studies

which leads to

Enhanced sensory input raises the excitability of alpha motor neurons, increasing the firing rate of already active motor units in the biceps femoris long-head.

Verified by multiple studies

which leads to

The increased firing rate elevates force production during submaximal contractions, contributing to early strength gains.

Verified by multiple studies

which leads to

After approximately three weeks, motor unit discharge rate plateaus, indicating reduced reliance on neural drive.

Verified by multiple studies

which leads to

Repeated high-force contractions induce sarcomerogenesis and increased fascicle length in the biceps femoris long-head, altering the muscle’s length-tension relationship.

Verified by multiple studies

which leads to

Structural changes increase the torque required to recruit and de-recruit motor units, improving force output efficiency without higher firing rates.

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

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.

86%

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.

81%

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.

79%

After performing eccentric exercises with one arm for eight weeks, the untrained arm becomes stronger, and this strength gain is closely linked to increased neural signals from the spinal cord to the muscles.

73%

Performing eccentric biceps exercises with one arm for 8 weeks leads to a measurable increase in nerve signal frequency to the biceps muscle on the opposite, untrained arm, suggesting improved neural activation of muscles not directly exercised.

72%