Maximal versus submaximal intensity stimulation with variable patterns

Abstract

It is essential to determine optimal parameters of stimulation to maintain muscle force during neuromuscular electrical stimulation (NMES). Protocols that increase in frequency and include doublets can prolong force output over time. However, stimulation intensity level could differentially affect muscle force output during variable-frequency NMES. We compared three intermittent stimulation patterns at maximal and submaximal intensities of stimulation of the median nerve: (1) a constant 20-HZ pattern; (2) 90 s at 20 HZ followed by a 90-s increase from 20 to 40 HZ; and (3) 90 s at 20 HZ followed by 90 s of doublets at 20 HZ. At submaximal intensities, the doublet pattern produced the highest overall force-time integral (FTI). At maximal intensities, the doublet pattern produced the lowest FTI and the increasing frequency pattern produced the least amount of fatigue. Thus, double-pulse stimulation was more effective during submaximal than maximal intensity NMES. These data demonstrate that intensity level must be taken into consideration when programming frequency patterns for NMES devices.

Alternating stimulation of synergistic muscles during functional electrical stimulation cycling improves endurance in persons with spinal cord injury

“…FES parameters that can affect force output include the timing of muscle group stimulation and characteristics of the stimulation train, such as stimulation intensity, frequency, and duration (Binder-Macleod, 1995;Binder-Macleod et al, 1995;Doucet and Griffin, 2008). Commercial FES cycles typically use constant frequency patterns of stimulation that co-activate a group of synergistic muscles.…”

Variable stimulation patterns for poststroke hemiplegia

“…23,32 Moreover, protocols that increased in stimulation frequency produced greater FTIs than constant-frequency patterns in young able-bodied adults. 20,32 In the present study, increasing stimulation frequency increased force output compared to constant frequency stimulation in older able-bodied adults but not in older adults paralyzed by stroke. It appears that the muscles of nonparalyzed individuals are more responsive to increases in frequency than those affected by paralysis.…”

“…Maximum evoked forces from each of the five 2-4-s trains (10,20,30,40, and 50 Hz) were compared across the three patterns (20 Hz, 20-40 Hz, and doublet), the two stimulation conditions (ablebodied and stroke), and the two time levels (pre-and postfatigue) using a multivariate analysis of variance (MANOVA) with univariate ANOVAs and Bonferroni corrections for post-hoc analysis. Starting, middle, and ending forces were also compared using the same model MANOVA.…”

“…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.…”

“…Recent studies have shown that increases in frequency during intermittent stimulation produced greater force over time than constant frequency protocols in young able-bodied adults 20 and in young 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.…”