Comparison of fatigue produced by various electrical stimulation trains

Abstract

Previous work has shown that variable-frequency trains (VFTs) that use an initial doublet to take advantage of the catch-like property of muscle produce more force in fatigued muscle than constant-frequency trains (CFTs); however, it is unclear whether repetitive activation with VFTs is more or less fatiguing than repetitive activation with CFTs. The purpose of this research was to investigate the forces and fatigue produced by various stimulation trains during repetitive isometric muscle contractions. Two force measurements, peak force and force-time integral, were used to measure the performance of the human quadriceps muscle. Three fatiguing protocols, each consisting exclusively of either CFTs, trains with an initial doublet (VFTs), or trains with doublets separated by longer intervals [doublet-frequency trains (DFTs)], were tested. In addition, force responses to each of the three train types were tested before and immediately following each fatiguing protocol. Regardless of the fatiguing protocol, the doublet-frequency testing trains produced the greatest peak forces and force-time integrals before and immediately following the fatiguing protocols. Repetitive activation with exclusively DFTs produced greater attenuation of the testing trains than repetitive activation with CFTs or VFTs. These results suggest that clinical applications of electrical stimulation to activate skeletal muscle may need to contain a combination of train types to optimize performance.

Catchlike property of skeletal muscle: Recent findings and clinical implications

“…6,9 -11 However, more recent studies have shown that repetitive activation with catchlike-inducing trains produces greater fatigue than repetitive activation with CFTs containing the same number of pulses. 18,21 This increased fatigability with repetitive catchlike-inducing train stimulation is probably due to greater forces produced by the catchlike-inducing trains during the fatigue protocol. 69,70 Abbate and colleagues found that the addition of three highfrequency pulses (at 400 Hz) at the start of a 60-Hz CFT did not produce any difference in the efficiency of high-energy phosphate consumption during stimulation of rat fast skeletal muscle, suggesting that the high-frequency burst of pulses caused a simultaneous increase both in performance measures and the energy expenditure of the muscle.…”

“…This observation is consistent with the higher fatigability seen during repetitive stimulation with catchlike-inducing trains than CFTs. 18,21 In another study, Abbate and colleagues studied the effects of adding a three-pulse 150-Hz burst either at the start of 350-ms long tetani or in the middle of 700-ms long tetani at four different frequencies (20 -60 Hz) on both the force output and the sarcoplasmic Ca 2ϩ concentration of single intact fibers of mouse flexor digitorum brevis. 1 The highfrequency burst resulted in a very brief increase in Ca 2ϩ concentration, whereas the increase in force was sustained for a much longer time, suggesting that the force potentiation after a high-frequency triplet is not exclusively due to sustained elevation of sarcoplasmic Ca 2ϩ concentration (Fig.…”

Variable stimulation patterns for poststroke hemiplegia

“…19,31,38,39 Others tested the use of doublets during the fatigue task itself in ablebodied younger adults; these studies produced mixed results. Some showed an increase in force over time, 4,6,11,33,51 while others showed a decrease 9,10 or no change. 35,52 Thomas et al 52 found that fatigue protocols with doublet trains produced the same force output as constant frequency trains in younger adults paralyzed by SCI.…”

“…34,50 Protocols that incorporate doublets (5-10 ms interpulse intervals) from the onset of the task have been shown to increase, 4,6,11,23,33,48,51 decrease, 9,10 or not change 35,52 force production over time compared to constant frequency stimulation in young adults. They have also been shown to exacerbate fatigue in older adults.…”

“…3 Protocols that used continuous doublets were more effective than those that used just one doublet at the start of each train in young ablebodied adults. 11,33 Intermittent stimulation protocols that began with constant frequency trains and then switched to trains that incorporated doublets later in the fatigue task were more effective than unchanging constant frequency stimulation in young able-bodied individuals 20,48 and in young adults paralyzed by SCI. 49 Although many studies have used able-bodied individuals as a model to test variable frequency patterns in young adults, very few studies have compared the effects of variable frequency patterns in individuals with and without paralysis in the same study.…”