Forward dynamic modelling of cycling for people with spinal cord injury.

A forward dynamic model was developed to predict the performance of Spinal Cord Injured (SCI) individuals cycling an isokinetic ergometer using Neuromuscular Electrical Stimulation (NMES) to elicit contractions of the quadriceps, hamstring and gluteal muscles. Computer simulations were performed using three inter-connected models: a kinematic model of segmental linkages, a muscle model predicting forces in response to stimulation, and a kinetic model predicting ergometer pedal forces resulting from muscle stimulation. Specific model parameters for SCI individuals were determined through measurements from isometric and isokinetic contractions of the quadriceps muscles elicited using surface stimulation. The muscle model was fitted to data resulting from these isolated experiments in order to tailor the model's parameters to characteristics of muscles from SCI individuals. Isometric data from a range of knee angles were used to fit tendon slack lengths to the rectus femoris and vastus muscles. Adjustments to the quadriceps moment arm function were not able to improve the match between measured and modelled knee extension torques beyond those using moment arms taken from available literature. Similarly, literature values for constants from the muscle force - velocity relationship provided a satisfactory fit to the decline in torque with angular velocity, and parameter fitting did not improve this fit. Passive visco-elastic resistance remained constant for all velocities of extension except the highest (240 deg/s). Since knee angular velocities this high were not experienced during cycling, a visco-elastic dampener was not included within the present cycling model. The rise and fall in torque following NMES onset and cessation were used to fit constants to match the rate of change in torque. Constants for the rise in torque following NMES onset were significantly altered by changes in knee angle, with more extended angles taking longer for torque to rise. This effect was small, however, within the range of angles used during cycling, and consequently was not included within the cycling model. The decline in torque after NMES cessation was not affected by knee angle. A period of five minutes cyclical isometric activity of the quadriceps resulted in torque declining by more than 75% from rested levels. The activation time constants were largely unaffected by this fatigue, however, with only a small increase in the time for torque to decline, and no change in rise time or the delay between stimulation changes and resulting torque changes. The cycling model, therefore, did not incorporate any effect for changes in activation timing with fatigue. Performance of the full model was evaluated through measurements taken from SCI individuals cycling a constant velocity ergometer using NMES elicited contractions of the quadriceps, hamstring and gluteal muscles. Pedal transducers measured forces applied to the pedals for comparison between measured and modelled values. A five minute period of continuous cycling using just the quadriceps muscles produced similar results to those found for isolated knee extension. External power output dropped by 50% over the five-minute period, however there was no change in the pattern of torque production with fatigue. Cycling experiments were conducted using single muscle groups across a range of NMES firing angles. Experimental protocols were designed to seek the firing angles for each muscle that maximised power output by that group. Changes in power output in response to firing angle changes were not large, however, in comparison to the effects of cumulative fatigue and inconsistent power output between trials. This lead to large uncertainties in the determination of those firing angles that maximised power output by each muscle. Results suggest that NMES firing angles to maximise power output by the quadriceps muscles were relatively similar for each subject. For the hamstring muscles, however, substantial differences were observed in the range of firing angles that maximised power output. Results for the gluteal muscles were variable, with some subjects not applying any measurable torque to the cranks, even with maximal stimulation applied. The model produced a good match to experimental data for the quadriceps muscles, both in the shape of pedal force curves and the firing angles that maximised external power output. The individual variability in hamstring responses was not, however, predicted by the model. Modification of the relative size of the hamstrings' moment arms about the hip and knee substantially improved the match between measured and modelled data. Analysis of results suggests that individual variability in the relative size of these moment arms is a major cause of variation in individual's response to hamstring stimulation. There were apparent limitations in the model's ability to predict the shape of crank torques resulting from stimulation of the gluteus maximus muscle. It is suggested that further research be conducted to enable modelling of this muscle using a range of fibre lengths and moment arms

THE EFFECT OF NEUROMUSCULAR ELECTRICAL STIMULATION (NMES) IN INDUCING MUSCLE HYPERTROPHY AND IMPROVEMENT IN MUSCLE TORQUE WITHN THE QUADRICEPS MUSCLE OF ELDERLY PEOPLE

Aging is associated with structural changes in skeletal muscles. One such change is loss of muscle mass. Muscle fiber atrophy is another structural transformation. Muscle fiber atrophy is selective to type II muscle fibers. The reduced mass of aging muscles has functional consequences like reduced performance of daily activities. Although exercise can be used to hypertrophy type II muscle fibers, it requires high intensity training that may not be feasible for elderly people. Due to the ability of neuromuscular electrical stimulation (NMES) to activate type II muscle fiber at relatively low intensity compared to voluntary exercises, NMES might be an alternative method to train type II muscle fibers in the elderly population. The purpose is to test the effectiveness of NMES compared to exercise that is performed at the same intensity in inducing structural changes in quadriceps muscle of elderly subjects. The aims are to 1) compare changes in muscle hypertrophy, 2) compare changes in quadriceps muscle power output, and 3) Compare changes in the performance-based functional power tests in subjects who receive NMES and those who receive isometric strengthening exercise at the same intensity level. Twenty subjects (71.2 +/- 4.41) were randomized to receive NMES or exercise. Computed tomography (CT), and muscle biopsy were performed to assess changes in cross sectional area (CSA) and fiber types of the quadriceps. Isokinetic quadriceps muscle power and performance based functional power were measured to assess changes in quadriceps strength and performance based physical function. The patterns of change from pre to post training on total quadriceps CSA, lean quadriceps CSA, and type IIA CSA were significantly higher for the NMES group. There was no difference between the groups in isokinetic quadriceps muscle power. The change in ramp power test from pre to post training was significantly higher for the NMES group. NMES might be an alternative to exercises in inducing type II fiber hypertrophy in older adults. NMES training induced improvements in performance based functional power tests compared to voluntary isometric exercise. There were no differences between the groups in the change in isokinetic quadriceps muscle power test scores

Effect of a neuromuscular electrical stimulation muscle strength training intervention on muscle force and mass, physical health and quality of life in people with spinal cord injury

Spinal cord injury (SCI) leads to significant deficits in muscle strength and mass, impacting negatively on physical health and quality of life (QoL). Physical rehabilitation techniques for people with SCI rely on constant updates and the accumulation of evidence regarding the efficacy of available and/or new physical interventions. Neuromuscular electrical stimulation (NMES) is already commonly used to activate skeletal muscles and subsequently reverse muscle atrophy, however NMES as a high-intensity “strength training” intervention appears to be a particularly promising technique for increasing muscle strength and mass and to subsequently improve physical health and quality of life (QoL) in people with SCI. Nonetheless, there are many factors limiting the use of standard NMES protocols, and further evidence pertaining to the use of high-intensity NMES strength training in clinical populations is warranted. The primary aim of the research described in this thesis was to examine the effects of NMES as a high-intensity muscle strength training intervention, specifically using wide-pulse width (1000 μs), low-to-moderate frequency (30 Hz) NMES combined with tendon vibration, on muscle strength and mass, physical health, symptoms of spasticity and QoL in people with SCI. This thesis includes two cross-sectional studies examining the effects of patellar tendon vibration (55 Hz, 7 mm amplitude) superimposed onto wide-pulse width (1000 μs) NMES (e.g. 30 Hz over 2 s) on the peak muscular (knee extensor) force and total impulse elicited by, and rate of recovery from, the intervention in healthy subjects (Study 1) and in people with chronic SCI (Study 2). The results of Study 1 revealed that superimposing tendon vibration onto wide-pulse width NMES leads to an increase in the muscle work performed before fatigue in only some individuals (i.e. positive responders, 50% of individuals in the current study), but decreases it in others (i.e. negative responders). However, it tends to reduce the voluntary force loss that was consistently experienced after a training session using high-intensity NMES, and may thus allow for additional exercise or rehabilitation work to be performed without ongoing voluntary muscle fatigue in healthy people. The results of Study 2 also identified positive and negative responders to tendon vibration in people with SCI, however the responses were less clear and a defined effect of tendon vibration superimposed onto NMES was not discerned. In Study 3, a 12-week (twice-weekly) high-intensity NMES strength training intervention was implemented in people with chronic SCI; based on results of Study 2, high-force contractions were evoked by NMES without superimposed tendon vibration. A significant increase in muscle mass (45%) and strength (tetanic evoked force; 31.8%), amelioration of spasticity symptoms, and improvement in some aspects of physical health and QoL were observed. Therefore, the use of high-intensity NMES strength training appears to be an effective rehabilitation tool to increase muscle force and mass, ameliorate symptoms of spasticity and improve physical and mental health outcomes in people with SCI

The effects of localized muscular fatigue on lower body running mechanics

Background: Running is a popular form of exercise and inherent to many sports. Running while fatigued has been associated with decrements in performance and increased risk of acute and overuse running injuries. However, the relative contributions to running mechanics from individual muscle(s) have not been clearly established and could help further elucidate risk factors and anatomical structure foci during training. This study’s purpose was to analyze alterations in kinematic, kinetic, and ground reaction force (GRF) variables with the onset of localized fatigue. It was hypothesized that knee flexor and extensor fatigue on separate occasions would increase impact forces, joint angles, joint moments, and powers compared to pre-fatigue values. Methods: Five healthy college-aged adults (2 males, 3 females: 23.60 +/- 1.14 years; 1.71 +/- 0.13m; 67.60 +/- 14.50kg) ran at 3.61m/s prior to and following isokinetic knee flexion and extension (concentric and eccentric) efforts for a total of three, two-minute runs. Motion capture and force data were used to calculate joint motion and loading throughout each run. Data were analyzed using RM-ANOVA evaluating kinematic and kinetic changes following fatigue of knee flexors and extensors for each run. Results: Maximum braking force significantly increased from immediate post-fatigue to twominutes post-fatigue (p=0.003; η2 p=0.677). Peak vertical GRF significantly (p<0.05) decreased from pre-fatigue (2.79 +/-0.09BW) to immediate post-fatigue (2.46+/-0.10BW) of the quadriceps. Propulsive knee power significantly (p<0.05) decreased from pre-fatigue (11.32+/- 1.74Nm/kg) to immediately post-fatigue (6.93+/-0.90Nm/kg) of the quadriceps. Knee abduction moments were significantly higher (p=0.001; η2 p=0.960) for running measures following hamstring fatigue over that of quadriceps fatigue. Discussion: Quadriceps fatigue showed the greatest pre-fatigue to immediately post-fatigue changes. Vertical impact peak force and propulsive knee power decreased significantly more immediately post- quadriceps fatigue than hamstring fatigue. Horizontal braking forces exhibited similar changes for both muscles over time, having significantly increased during the fatigued run.Thesis (M.S.

A Comparison of Multipath and Conventional Neuromuscular Electrical Stimulation

Neuromuscular electrical stimulation (NMES) is the use of an electrical current for the purpose of eliciting a muscular response, and these treatments are most often used clinically for the specific purpose of increasing quadriceps strength. It is commonly accepted that the effectiveness of NMES for this purpose is primarily determined by the NMES training intensity. However, spatially limited motor unit recruitment, fatigue and discomfort negatively impact NMES-induced torque, which subsequently reduces NMES training intensities. Due to the importance of NMES training intensity, a substantial amount of research has focused on strategies designed to increase NMES-induced torque production, as well as to reduce NMES-induced fatigue and discomfort. However, authors have indicated that additional strategies are needed, as many of the strategies supported by empirical evidence cannot be easily applied in clinical settings. The Kneehab® XP (Theragen LLC, Leesburg, VA) is an electrical stimulator that incorporates a novel multipath current distribution strategy (m-NMES) marketed to address the primary factors limiting NMES training intensity, and as such it has gained a significant amount of attention in the literature. Relative to conventional NMES (c-NMES), authors have reported improved outcomes while using the novel m-NMES but due to a series of methodological limitations the influence of the multipath current distribution strategy on these outcomes remains unclear. Therefore, the purpose of this project was to further investigate the influence that m-NMES has on NMES related outcomes. A convenience sample of 21 participants completed two basic studies designed to compare the influence of m-NMES and c-NMES on maximum comfortable stimulus intensity and NMES-induced peak torque, as well as fatigue and discomfort related outcomes. The statistical analyses of each study did not reveal any significant differences across the two conditions deemed to be clinically relevant. Therefore, it does not appear that the novel multipath current distribution method influences the outcomes included during this project in a clinically meaningful manner. The large declines in NMES-induced torque that occurred, irrespective of the NMES condition, suggest the need for the development of additional strategies

TEMPORAL NEUROMUSCULAR ALTERATIONS OF THE QUADRICEPS AFTER UNILATERAL ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION

Objective: The primary aim of this research was to examine the temporal pattern of neuromuscular quadriceps deficits in both the involved and uninvolved limbs of patients assigned to the control group after anterior cruciate ligament reconstruction (ACLr), by assessing quadriceps strength, voluntary activation, and corticomotor excitability prior to surgery (baseline), three months after ACLr, and six months after ACLr. A secondary aim of this research was to determine whether quadriceps strength, voluntary activation, and/or corticomotor excitability assessed in patients prior to ACLr and/or at three months after surgery, is predictive of lower extremity postural control and/or self-reported function at six months after ACLr. Lastly, a tertiary aim of this research was to determine if a 12-week home-based neuromuscular electrical stimulation (Home-NMES) program elicits greater bilateral improvements in quadriceps strength, voluntary activation, and corticomotor excitability of patients at three and six months after ACLr compared to a 12-week standard home-exercise program (control group). Participants: Fifty patients scheduled to undergo unilateral ACLr were randomly allocated to the home-NMES group (19 Female, 6 Male; age: 18.9 ± 5.4 years; height: 170.8 ± 9.7 cm; weight: 74.6 ± 18.5 kg; 28.0±20.0 days-post-injury) or control group (14 Female, 11 Male; age: 19.4 ± 4.5 years; height: 171.1 ± 11.5 cm; weight: 70.7 ± 11.9 kg). Methods: A randomized clinical trial design was used in this study. Prior to ACLr, isometric quadriceps strength and voluntary quadriceps activation were assessed in both limbs of patients, and corticomotor excitability was assessed in the involved limb. Three days after ACLr, both groups were instructed to begin their allocated interventions. The Home-NMES group administered NMES to their involved limb’s quadriceps three sessions a day for 15 minutes, and five days a week for 12 weeks using a portable NMES device. The control group was treated according to the current standard-of-care, but they were also instructed to perform volitional isometric quadriceps contractions for the same duration and frequency as the Home-Based NMES protocol. The outcomes measures were reassessed in both groups at three and six months post-ACLr. Main Outcome Measures: Quadriceps strength and voluntary activation were assessed using maximal voluntary isometric contractions and the superimposed burst technique, respectively. Normalized peak knee extension torque and central activation ratio were used to quantify isometric quadriceps strength and activation, respectively. Corticomotor excitability was evaluated with transcranial magnetic stimulation, and quantified with active motor threshold). The Y-balance test anterior reach (YBT-A) and Knee Injury and Osteoarthritis Outcome Score (KOOS) were used to assess the patients lower extremity knee function at six months post-ACLr. Statistical Analyses: Specific Aim 1: A 2x3 (limb x time) mixed model, ANOVA with repeated measures was performed in the control group to assess differences between the involved limb and the uninvolved limb for isometric quadriceps strength, and voluntary quadriceps activation over time. A one-way mixed model, ANOVA with repeated measures was performed in the control group to assess differences in corticomotor excitability over time. Post-hoc comparisons were performed when appropriate. Specific Aim 2: Separate, mixed model, linear regression analyses were performed in the control group (involved limb) to determine the effect that the neuromuscular quadriceps outcome measures assessed at baseline and 3 months post-ACLr, had on lower extremity knee functional outcome measures assessed at 6 months post-ACLr. Specific Aim 3: A 2x2x3 (group x limb x time) mixed model, ANOVA with repeated measures was performed to assess group differences between the involved limb and the uninvolved limb in isometric quadriceps strength, and voluntary quadriceps activation over time. A 2x3 (group x time) mixed model, ANOVA with repeated measures was performed to assess group differences in corticomotor excitability over time. Post-hoc comparisons were performed when appropriate. Results: Aim 1: Patients demonstrated lower quadriceps strength on their involved limb compared to their uninvolved limb at baseline, three months post-ACLr, and six months post-ACLr. Quadriceps strength progressively decreased in the involved limb of patients from baseline to 3 months post-ACLr, baseline to 6 months post-ACLr, and increased from 3 months to 6 months post-ACLr. Quadriceps strength was also decreased in the uninvolved limb of patients from baseline to 6 months post-ACLr. ). Irrespective of when it was assessed, voluntary quadriceps activation was higher in the involved limb of patients compared to their uninvolved limb. There were no changes in corticomotor excitability of the involved limb over time. Specific Aim 2: The quadriceps strength of patients at three months post-ACLr had a significant positive effect on their 6-month YBT-A performance KOOS score. ). Neither voluntary quadriceps activation or corticomotor excitability or AMT (at baseline or 3-month post-ACLr) had a significant effect on any of the 6-month lower extremity functional outcome measures. Specific Aim 3: Irrespective of limb or when it was assessed, quadriceps strength was higher in the control group compared to the Home-NMES group. Both groups demonstrated lower quadriceps strength on their involved limbs compared to their uninvolved limbs at baseline, three months post-ACLr, and six months post-ACLr. Quadriceps progressively decreased in the involved limbs of both groups from baseline to three months post-ACLr and baseline to six months post-ACLr, and increased from three months to six months post- ACLr. At baseline, voluntary quadriceps activation was higher in the involved limbs of both groups compared to their uninvolved limbs. There were no group differences or changes over time observed in the involved limb of both groups with corticomotor excitability. Conclusion: Although quadriceps weakness is more apparent in the involved limb of patients after ACLr, the quadriceps strength of their uninvolved limb was also affected. Clinicians are encouraged to not rely on a quadriceps strength limb symmetry index when making return-sport-decisions for their patients after recovering from ACLr. The quadriceps in the uninvolved limb of patients demonstrated more inhibition, which may explain the quadriceps strength deficits observed in the uninvolved limb of patients following ACLr. To reduce the risk of subsequent injury upon return-to-sport and protect against the development of knee OA, we recommend that clinicians incorporate bilateral interventions aimed at restoring quadriceps strength and disinhibiting the quadriceps. Intensive quadriceps strengthening should be performed in the early stages of ACLr rehabilitation, so that lower extremity function can be improved in patients later on. Lastly, the effectiveness of home-based NMES as a modality for restoring quadriceps strength and activation in patients after ACLr is inconclusive. Home-based NMES provides patients with the ability to receive higher doses of NMES to the quadriceps; but its effectiveness may be limited by low contraction intensities and poor treatment compliance in patients