Lisa Griffin

Functional electrical stimulation cycling improves body composition, metabolic and neural factors in persons with spinal cord injury

Persons with spinal cord injury (SCI) are at a heightened risk of developing type II diabetes and cardiovascular disease. The purpose of this investigation was to conduct an analysis of metabolic, body composition, and neurological factors before and after 10 weeks of functional electrical stimulation (FES) cycling in persons with SCI. Eighteen individuals with SCI received FES cycling 2-3 times per week for 10 weeks. Body composition was analyzed by dual X-ray absorptiometry. The American Spinal Injury Association (ASIA) neurological classification of SCI test battery was used to assess motor and sensory function. An oral glucose tolerance (OGTT) and insulin-response test was performed to assess blood glucose control. Additional metabolic variables including plasma cholesterol (total-C, HDL-C, LDL-C), triglyceride, and inflammatory markers (IL-6, TNF-alpha, and CRP) were also measured. Total FES cycling power and work done increased with training. Lean muscle mass also increased, whereas, bone and adipose mass did not change. The ASIA motor and sensory scores for the lower extremity significantly increased with training. Blood glucose and insulin levels were lower following the OGTT after 10 weeks of training. Triglyceride levels did not change following training. However, levels of IL-6, TNF-alpha, and CRP were all significantly reduced.

Changes in resting heart rate variability across the menstrual cycle

Heart rate variability (HRV) is a noninvasive indicator of autonomic control. This study examines HRV changes across a normal menstrual cycle and proposes a novel piecewise function controlling for the effects of breathing on HRV spectral parameters. A resting ECG was collected from 13 women at five points in their menstrual cycle. Both heart rate and breathing rate increased across the cycle (p < .01) while time-domain variability decreased (p = .04). Use of the piecewise function for breathing rate in HRV spectral analysis was confirmed by a substantial increase in model goodness-of-fit. HRV spectral parameters, controlled for breathing with the piecewise function, confirm that the decrease in variability is likely due to a parasympathetic withdrawal, since high frequency HRV decreases (p = .02).

VARIABLE STIMULATION PATTERNS FOR POSTSTROKE HEMIPLEGIA

Neuromuscular electrical stimulation can improve motor function in those affected by paralysis, but its use is limited by a high rate of muscular fatigue. Variable stimulation patterns have been examined in young adults with and without spinal cord injury, but much less investigation has been devoted to studying the effects of variable stimulation patterns administered to older adults or those paralyzed by stroke. Significant changes occur in the neuromuscular system with age that may affect the response to variable stimulation patterns. We administered three, 3‐min intermittent stimulation patterns to the median nerves of 10 individuals with hemiplegia from stroke and 10 age‐matched able‐bodied adults: (1) constant 20 HZ, (2) a pattern that began at 20 HZ and progressively increased to 40 HZ in the latter half of the task, and (3) a 20‐HZ pattern that switched to a 20‐HZ doublet pattern after 90 s. In the able‐bodied group the doublet pattern produced significantly higher force time integrals (FTI) (1409.72 ± 3.15 N · s) than the 20–40‐HZ pattern (1067.46 ± 1.15 N · s) or the 20‐HZ pattern (831 ± 1.87 N · s). In the poststroke individuals the doublet pattern also produced the highest FTI (724.04 ± 2.02 N · s), and there was no significant difference between the 20–40‐HZ (636.42 ± 1.65 N · s) and 20‐HZ (583.64 ± 3.02 N · s) patterns. These results indicate that protocols that incorporate doublets in the later stages of fatigue are effective in older adults and in older adults with paralysis from stroke.

Postactivation potentiation and muscular endurance training.

Introduction: The aim of this study was to investigate muscle twitch force potentiation after voluntary conditioning contractions (CC) of various intensities and the CC duration necessary to achieve maximal potentiation before and after muscular endurance training. Methods: Fourteen healthy men and women (23.6 ± 0.96 years of age) performed repeated CCs of 25%, 50%, and 100% maximal voluntary contraction of the adductor pollicis muscle until maximal potentiation. CCs were followed by electrically evoked twitches. The training group performed a fatigue task and endurance trained for 8 weeks. Results: Endurance time increased by 79.8 ± 22.5% posttraining. Potentiation occurred after all CC intensities and was greater after training. The CC duration needed to achieve maximal potentiation decreased as CC intensity increased. Potentiation was greater during the fatigue task after compared to before training and was correlated with endurance time. Conclusion: An increase in muscle force potentiation may function as a mechanism to prolong muscular endurance. Muscle Nerve, 2012

Menstrual cycle mediates vastus medialis and vastus medialis oblique muscle activity.

PURPOSE Sports medicine professionals commonly describe two functionally different units of the vastus medialis (VM), the VM, and the vastus medialis oblique (VMO), but the anatomical support is equivocal. The functional difference of the VMO is principle to rehabilitation programs designed to alleviate anterior knee pain, a pathology that is known to have a greater occurrence in women. The purpose of this study was to determine whether the motor units of the VM and VMO are differentially recruited and if this recruitment pattern has an effect of sex or menstrual cycle phase. METHODS Single motor unit recordings from the VM and VMO were obtained for men and women during an isometric ramp knee extension. Eleven men were tested once. Seven women were tested during five different phases of the menstrual cycle, determined by basal body temperature mapping. The recruitment threshold and the initial firing rate at recruitment were determined from 510 motor unit recordings. RESULTS The initial firing rate was lower in the VMO than that in the VM in women (P < 0.001) but not in men. There was no difference in recruitment thresholds for the VM and VMO in either sex or across the menstrual cycle. There was a main effect of menstrual phase on initial firing rate, showing increases from the early follicular to late luteal phase (P = 0.003). The initial firing rate in the VMO was lower than that in the VM during ovulatory (P = 0.009) and midluteal (P = 0.009) phases. CONCLUSION The relative control of the VM and VMO changes across the menstrual cycle. This could influence patellar pathologies that have a higher incidence in women.

Maximal versus submaximal intensity stimulation with variable patterns.

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. Muscle Nerve, 2008

Effect of random interpulse interval modulation on neuromuscular fatigue

Neuromuscular endurance during electrical stimulation may be enhanced if naturally occurring motor unit firing patterns are used. Variability in the interpulse interval (IPI) distribution may enable brief periods of rest and optimization of force output. Nine individuals participated in three 3‐minute fatigue protocols of the thenar muscles elicited by supramaximal stimulation of the median nerve. All protocols consisted of a mean IPI of 33.3 ms and differed only in the type of IPI modulation, which was constant (0%), random (±20%), or ramped from 0% to ±20%. M‐wave amplitude declined following all protocols and the reduction was smallest following the ramp protocol. There was no significant difference among the starting or final forces or between the overall force–time integrals for the three protocols. Thus, IPI variability did not improve endurance time during electrical stimulation and the M‐wave amplitude was not a reliable indicator of muscle force output. Muscle Nerve, 2007

High- Versus Low-Frequency Stimulation Effects on Fine Motor Control in Chronic Hemiplegia: A Pilot Study

Abstract Background: The optimal parameters of neuromuscular electrical stimulation (NMES) for recovery of hand function after stroke are not known. This clinical pilot study examined whether higher or lower frequencies are more effective for improving fine motor control of the hand in a chronic poststroke population. Methods: A 1-month, 4 times per week, in-home regimen of either a high-frequency (40 Hz) or low-frequency (20 Hz) NMES program was applied to the hemiplegic thenar muscles of 16 persons with chronic stroke. Participants were identified a priori as having a low level of function (LF) or a high level of function (HF). Outcome measures of strength, dexterity, and endurance were measured before and after participation in the regimen. Results: LF subjects showed no significant changes with either the high- or the low-frequency NMES regimen. HF subjects showed significant changes in strength, dexterity, and endurance. Within this group, higher frequencies of stimulation yielded strength gains and increased motor activation; lower frequencies affected dexterity and endurance. Conclusions: The results suggest that higher frequencies of stimulation could be more effective in improving strength and motor activation properties and that lower frequencies may affect coordination and endurance changes. Results also indicate that persons with a higher functional level of recovery may respond more favorably to NMES regimens, but further study with larger patient groups is warranted.

Muscle spasticity associated with reduced whole-leg perfusion in persons with spinal cord injury

Abstract Objective To determine the association between peripheral blood flow and spasticity in individuals with spinal cord injury (SCI). Design A cross-sectional study with measurements of muscle spasticity and whole-limb blood flow in individuals with SCI. Setting University of Texas at Austin and Brain & Spine Recovery Center, Austin, TX, USA. Participants Eighteen individuals (14 males and 4 females) with SCI were classified into high (N = 7), low (N = 6), and no (N = 5) spasticity groups according to the spasticity levels determined by the modified Ashworth scale scores. Interventions Whole-limb blood flow was measured in the femoral and brachial arteries using Doppler ultrasound and was normalized to lean limb mass obtained with dual-energy X-ray absorptiometry. Outcome measures Limb blood flow and muscle spasticity. Results Age, time post-SCI, and the American Spinal Injury Association impairment scale motor and sensory scores were not different among groups with different muscle spasticity. Femoral artery blood flow normalized to lean leg mass was different (P = 0.001) across the three spasticity groups (high 78.9 ± 16.7, low 98.3 ± 39.8, no 142.5 ± 24.3 ml/minute/kg). Total leg muscle spasticity scores were significantly and negatively correlated with femoral artery blood flow (r = −0.59, P < 0.01). There was no significant difference in brachial artery blood flow among the groups. Conclusions Whole-leg blood flow was lower in individuals with greater spasticity scores. These results suggest that a reduction in lower-limb perfusion may play a role, at least in part, in the pathogenesis leading to muscle spasticity after SCI.

Entrainment of vastus medialis complex activity differs between genders

Introduction: That the vastus medialis oblique (VMO) is a functional unit of the vastus medialis (VM) is disputed. Delayed VMO activation predicts patellofemoral pain, which has higher rates in women. Methods: Single MUs and surface electromyogram (EMG) were collected from the VMO and VM of 9 men and 9 women. Men were tested once; women were tested during 5 menstrual phases. Coherence was assessed for motor unit (MU) firings within and between the VM and VMO using multilevel logistic models to determine statistical significance. Results: Compared with women, men have 741% (MU pairs) and 256% (MU‐EMG pairs) greater odds of common drive (0–5 Hz) coherent oscillations. MU pairs from the VMO and the dual VM/VMO complex have 228% and 212% greater odds of coherent oscillations in the beta band (15–35 Hz) compared with VM pairs. Conclusions: The VM and VMO are neurologically different muscles; control of the VM complex is sexually dimorphic. Muscle Nerve 53: 633–640, 2016