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Updated: Mar 11, 2026
Simultaneous Intracellular Recording of a Lumbar Motoneuron and the Force Produced by its Motor Unit in the Adult Mouse In vivo
Published on: December 5, 2012
Comparison of the ballistic contractile responses generated during microstimulation of single human motor axons with
Michael Leitch1, Vaughan G Macefield1
1School of Medicine, Western Sydney University, Locked Bag 1797, 183 Narellan Road, Penrith, New South Wales, 2751, Australia.
Introduction:
Ballistic contractions are induced by brief, high-frequency (60-100 Hz) trains of action potentials in motor axons. During ramp voluntary contractions, human motoneurons exhibit significant discharge variability of ∼20% and have been shown to be advantageous to the neuromuscular system. We hypothesized that ballistic contractions incorporating discharge variability would generate greater isometric forces than regular trains with zero variability.
Methods:
High-impedance tungsten microelectrodes were inserted into human fibular nerve, and single motor axons were stimulated with both irregular and constant-frequency stimuli at mean frequencies ranging from 57.8 to 68.9 Hz.
Results:
Irregular trains generated significantly greater isometric peak forces than regular trains over identical mean frequencies.
Conclusions:
The high forces generated by ballistic contractions are not based solely on high frequencies, but rather a combination of high firing rates and discharge irregularity. It appears that irregular ballistic trains take advantage of the "catchlike property" of muscle, allowing augmentation of force. Muscle Nerve 56: 292-297, 2017.
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