Back to "The torque at which motor units were de-..."
Strong Support
mechanistic
Analysis v3
History

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...

31
Pro
0
Against

Mechanism

Synthesis from 1 study

How it works

Your hamstring muscles get longer and more layered after weeks of Nordic hamstring exercises, which changes how they send signals back to your spinal cord when relaxing. These altered signals make your muscles stay active longer at high force levels, which is why it takes nine weeks—not three—to...

Most probable mechanism

In Simple Terms

After repeated eccentric training, the hamstring muscle fibers grow longer and add more contractile units in series, which changes how the muscle stretches and sends signals back to the spinal cord. These altered signals make the motor neurons keep firing longer as the muscle relaxes, so they stay active at higher force levels before turning off. This change takes time because it depends on physical remodeling of the muscle, not just faster nerve signals.

Causal chain
1

Repeated eccentric contractions impose high mechanical stress on hamstring muscle fibers, triggering structural adaptations including sarcomerogenesis and increased fascicle length.

Verified by multiple studies
which leads to
2

The elongated muscle architecture increases passive tension and alters the sensitivity of muscle spindles during lengthening and relaxation phases.

Supported by evidence
which leads to
3

Enhanced spindle afferent feedback during torque decline provides sustained excitatory input to alpha motor neurons, delaying the cessation of motor unit activity.

Supported by evidence
which leads to
4

This prolonged neural drive raises the torque threshold at which motor units are de-recruited, allowing force maintenance at higher loads during relaxation.

Verified by multiple studies

Less supported by current evidence, but not ruled out

In Simple Terms

Prolonged training may reduce the natural braking system in the spinal cord that normally stops motor neurons from firing, allowing them to stay active longer during relaxation.

Causal chain
1

Chronic eccentric loading alters spinal cord circuitry, reducing presynaptic inhibition of Ia afferent terminals.

Indirect evidence only
which leads to
2

This increases the strength of sensory signals reaching motor neurons during muscle relaxation.

Indirect evidence only
which leads to
3

The enhanced sensory input prolongs motor neuron firing, raising the de-recruitment torque threshold.

Indirect evidence only

Evidence from Studies

Supporting (1)

31

Community contributions welcome

31

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)

0

Community contributions welcome

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.

Sign up to see full verdict

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.

31
0
95%

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.

31
0
88%

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, suggesting that initial strength improvements are driven by nervous system changes that become less influential over time.

31
0
79%

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.

82
0
75%

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 improvement in muscle force production.

31
0
74%