Research Article

Experimental Brain Research

, Volume 218, Issue 4, pp 601-607

First online:

The stability of Mmax and Hmax amplitude over time

  • Penelope A. McNultyAffiliated withNeuroscience Research Australia, University of New South Wales Email author 
  • , Christine T. ShinerAffiliated withNeuroscience Research Australia, University of New South Wales
  • , Ganesha K. ThayaparanAffiliated withNeuroscience Research Australia, University of New South Wales
  • , David BurkeAffiliated withInstitute of Clinical Neurosciences, The University of Sydney and Royal Prince Alfred Hospital

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The stability of the maximal muscle response (Mmax) is critical to H reflex methodology. It has previously been reported that the amplitude of Mmax declines over time. If reproducible, this finding would have implications for all experimental studies that normalise the output of the motoneurone pool against the M wave. We investigated the effect of time on changes in Mmax and the maximal H reflex (Hmax) evoked at 4-s intervals over 60 min. To identify an influence of homosynaptic depression, we extended the interstimulus interval to 10 s and the time to 100 min. Two recording montages over soleus were used to ensure that interelectrode distance was not a critical factor. The soleus Mmax and H reflex were evoked by stimulation of the tibial nerve in the popliteal fossa in 7 subjects who sat with the knee flexed to 30° and the ankle plantar flexed by ~30°. We found no change in the pooled data for Mmax, Hmax, a reflex 50% of maximal, or the current required to produce it. However, one subject had a statistically significant increase in Mmax and a concurrent decrease in Hmax regardless of the interstimulus interval. On average, there was no change in the Hmax/Mmax ratio over time. While both Mmax and Hmax may change in response to many factors, these results suggest that, typically, time is not one of them.


Maximal muscle response H reflex Spinal circuitry excitability Human soleus muscle Motor control