Carvell, PhD, PTUniversity
MOTOR UNIT RECRUITMENT: MUP Firing Rates
2 & Table 1 IN: T. Eken, Spontaneous Electromyographic Activity in Adult Rat Soleus Muscle. J Neurophysiol 80: 365-376, 1998.
(EMG) recordings are used to measure motor unit activity. Surface EMG measures overall levels of muscle activity
(see SMCs In Action) but individual motor unit potentials cannot be reliably isolated in these
recordings. Special indwelling electrodes are required to see individual motor unit potentials (MUPs). During low
levels of tonic activity individual MUPs can be isolated(Fig 2 and 34-12). Average firing rates tend to be
< 25 Hz but there are exceptions (see Table 1 and fig 34-12). Isolating individual MUPs is difficult with
phasic activities requiring rapid and/or large forces since the MUPs tend to overlap even when using
indwelling electrode recordings & gradual force increments (see fig 34-12).
34-12 p 687
Eken Fig 2 p 368
Eken Table 1 p
1- 4 = MUPs
during 4 trials of low levels of tonic activity in Rat Soleus Muscle