Abstract
PurposeA critical limitation with transcutaneous neuromuscular electrical stimulation is the rapid onset of muscle fatigue. We have previously demonstrated that spatially distributed sequential stimulation (SDSS) shows a drastically greater fatigue-reducing ability compared to a single active electrode stimulation (SES). The purposes of this study were to investigate (1) the fatigue-reducing ability of SDSS in more detail focusing on the muscle contractile properties and (2) the mechanism of this effect using array-arranged electromyogram (EMG).MethodsSDSS was delivered through four active electrodes applied to the plantarflexors, sending a stimulation pulse to each electrode one after another with 90° phase shift between successive electrodes. In the first experiment, the amount of exerted ankle torque and the muscle contractile properties were investigated during a 3 min fatiguing stimulation. In the second experiment, muscle twitch potentials with SDSS and SES stimulation electrode setups were compared using the array-arranged EMG.ResultsThe results demonstrated negligible torque decay during SDSS in contrast to considerable torque decay during SES. Moreover, small changes in the muscle contractile properties during the fatiguing stimulation using SDSS were observed, while slowing of muscle contraction and relaxation was observed during SES. Further, the amplitude of the M-waves at each muscle portion was dependent on the location of the stimulation electrodes during SDSS.ConclusionWe conclude that SDSS is more effective in reducing muscle fatigue compared to SES, and the reason is that different sets of muscle fibers are activated alternatively by different electrodes.
Highlights
Transcutaneous neuromuscular electrical stimulation (TNMES) is a method to electrically activate muscle fibers by applying stimulation electrodes on the skin above muscles and stimulating branches of motor nerve
While TNMES has succeeded in assisting individuals with neuromuscular disorders, a critical limitation with this rehabilitative approach is the rapid onset of muscle fatigue during repeated contractions (Bickel et al 2011; Shields and Dudley-Javoroski 2006; Mizrahi et al 1997), which results in muscle force decay and slowing of muscle contractile properties (Jones 2010; Enoka and Stuart 1992)
We demonstrated that the spatially distributed sequential stimulation did not affect much the muscle contractile properties during the fatiguing stimulation, whereas single active electrode stimulation slowed down muscle contraction progression and relaxation
Summary
Transcutaneous neuromuscular electrical stimulation (TNMES) is a method to electrically activate muscle fibers by applying stimulation electrodes on the skin above muscles and stimulating branches of motor nerve. In individuals with neuromuscular disorders, fatigue develops within the motor unit and is associated with such factors as depletion of substances, accumulation of catabolites, and problems in excitation–contraction coupling (Biering-Sorensen et al 2009; Pelletier and Hicks 2009; Shields 1995) Due to these major factors, the paralyzed muscles show greater fatigability than healthy muscles (Gerrits et al 1999, 2003; Lenman et al 1989; Thomas 1997a, b; Shields 1995), further compounding the problem of muscle fatigue during TNMES. Developing means to counter force loss during electrical stimulation has received much interest (Gauthier et al 1992; Stein et al 1992; Binder-Macleod and McLaughlin 1997; Riess and Abbas 2001)
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