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M. Gabyzon1, Y. Awad1
1University of Haifa, Physical Therapy, Haifa, Israel
Background: Short interphase intervals (IPIs) within biphasic symmetrical pulses have been demonstrated to enhance maximally electrically induced isometric contractions (EIC). However, IPI effects have not been previously studied in muscles stimulated at the highest tolerated current intensity.
Purpose: The aim of the current study was to determine whether the insertion of an IPI at the highest tolerated current intensity affects the strength of EIC, degree of discomfort, and sensory and motor thresholds of the wrist extensor muscles.
Methods: Eighteen volunteers (mean age 25.5, SD±3.97 years) participated in a repeated-measures trial. Five parameter settings were used to stimulate the wrist extensors: monophasic pulses with phase durations (PD) 200µs, and biphasic pulses with PDs of either 200µs or 500 µs, applied with/without an IPI of 200µs duration. Order of settings was randomized, and current was set at the maximum intensity tolerated by each subject.
Results: IPIs applied at the maximally tolerated current intensity did not increase the strength of the EICs and did not reduce the degree of discomfort or the sensory and motor thresholds. These findings were not dependent on the PDs.
Conclusion(s): Insertion of an IPI within the biphasic current during stimulation of the wrist muscle yielded no advantage in terms of strength of EIC or degree of discomfort. These results contradict previous studies indicating stronger contractions when an IPI is inserted during stimulation at a predetermined submaximal current intensity.
Implications: These results are clinically significant, as most applications of neuromuscular electrical stimulation utilize the highest tolerated current intensity. Additional studies involving other muscle groups, electrode size and locations, and phase parameters, are warranted.
Funding, acknowledgements: None
Keywords: interphase interval, current intensity, electrically induced contractions
Topic: Electrophysical & isothermal agents
Did this work require ethics approval? Yes
Institution: University of Haifa
Committee: Institutional Review Board
Ethics number: 146/18
All authors, affiliations and abstracts have been published as submitted.
