Reducing muscle fatigue during transcutaneous neuromuscular electrical stimulation by spatially and sequentially distributing electrical stimulation sources

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.

Fatigue reduction during aggregated and distributed sequential stimulation

“…Although Fatigue Index, as defined here is a common measure used to characterize fatigue, it does not capture performance throughout fatiguing trains. To do this, Torque Peak Mean was calculated as: …”

“…This technique involves “sequential” rotation of stimulation pulses between multiple active electrodes positioned over the muscle belly (SEQ). To date, several SEQ techniques have been used and have effectively reduced fatigue in human studies . Our group has been developing a technique whereby multiple active electrodes are “aggregated” (AGGR‐SEQ) at the same site and over the same area as the single active electrode used during CONV stimulation.…”

“…Our group has been developing a technique whereby multiple active electrodes are “aggregated” (AGGR‐SEQ) at the same site and over the same area as the single active electrode used during CONV stimulation. We have described this previously as spatially distributed sequential stimulation . We have shown that AGGR‐SEQ stimulation can reduce fatigue of healthy and paralyzed plantarflexors, dorsiflexors, knee flexors, and knee extensors by activating separate motor unit populations at reduced discharge rates beneath each AGGR‐SEQ electrode …”

Closed-Loop Asynchronous Neuromuscular Electrical Stimulation Prolongs Functional Movements in the Lower Body

“…Let be a continuously differentiable function, defined as (29) which satisfies the following inequalities: (30) where are continuous, positive definite functions defined as , where was defined in (27) and are positive constants. The time derivative of (29) exists almost everywhere (a.e.)…”

Stimulation map for control of functional grasp based on multi-channel EMG recordings

“…The technology that has allowed fabrication of array electrodes for stimulation and the development of advanced electronic stimulators has provided a basis for determining how selective stimulation of the forearm muscles can be achieved [e.g., [7][8][9][10]. These studies led to two major conclusions: 1) small electrodes that are positioned appropriately can improve the selectivity of stimulation [11][12][13][14] and 2) stimulation delivered asynchronously through several small electrodes at a lower frequency (approximately 10 pulses per second) rather than a single large electrode at a high frequency (approximately 30 pulses per second) allows prolonged stimulation that results in fused contraction [15][16][17] . A remaining challenge is how to easily and quickly select the number of electrodes and their relative positions with respect to the excitable tissue to produce adequate prehension and a safe and strong grasp with minimal wrist interference.…”