Physiological recruitment of motor units by high-frequency electrical stimulation of afferent pathways
Journal article, 2015

Neuromuscular electrical stimulation (NMES) is commonly used in rehabilitation, but electrically evoked muscle activation is in several ways different from voluntary muscle contractions. These differences lead to challenges in the use of NMES for restoring muscle function. We investigated the use of low-current, high-frequency nerve stimulation to activate the muscle via the spinal motoneuron (MN) pool to achieve more natural activation patterns. Using a novel stimulation protocol, the H-reflex responses to individual stimuli in a train of stimulation pulses at 100 Hz were reliably estimated with surface EMG during low-level contractions. Furthermore, single motor unit recruitment by afferent stimulation was analyzed with intramuscular EMG. The results showed that substantially elevated H-reflex responses were obtained during 100-Hz stimulation with respect to a lower stimulation frequency. Furthermore, motor unit recruitment using 100-Hz stimulation was not fully synchronized, as it occurs in classic NMES, and the discharge rates differed among motor units because each unit was activated only after a specific number of stimuli. The most likely mechanism behind these observations is the temporal summation of subthreshold excitatory postsynaptic potentials from Ia fibers to the MNs. These findings and their interpretation were also verified by a realistic simulation model of afferent stimulation of a MN population. These results suggest that the proposed stimulation strategy may allow
generation of considerable levels of muscle activation by

Author

Jakob L. Dideriksen

University Medical Center Göttingen

Silvia Muceli

University Medical Center Göttingen

Strahinja Dosen

University Medical Center Göttingen

Christopher M Laine

University Medical Center Göttingen

Dario Farina

University Medical Center Göttingen

Journal of Applied Physiology

8750-7587 (ISSN) 1522-1601 (eISSN)

Vol. 118 3 365-376

Subject Categories

Sport and Fitness Sciences

Physiology

Public Health, Global Health, Social Medicine and Epidemiology

DOI

10.1152/japplphysiol.00327.2014

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Latest update

4/19/2021