Long-term adaptation to electrically induced cycle training in severe spinal cord injured individuals

Myosin heavy-chain isoform distribution, fibre-type composition and fibre size in skeletal muscle of patients on haemodialysis

OBJECTIVE

Chronic uraemia is associated with abnormalities in skeletal muscles, which can affect their working capacity. It is also well known that the fibre-type composition of skeletal muscles influences endurance, muscle strength and power. In this study we therefore determined the size and distribution of muscle fibres and the myosin heavy-chain (MHC) isoform composition in patients on haemodialysis (HD) in order to establish any differences with values for untrained control subjects.

MATERIAL AND METHODS

Muscle biopsies were obtained from the vastus lateralis muscle of 14 non-diabetic patients on HD. The size and distribution of muscle fibres were evaluated using adenosine triphosphate synthase (ATPase) histochemistry, whilst MHC isoform composition was determined in muscle homogenates using sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Values were compared to those for a group of age-, gender- and BMI-matched untrained control subjects. The aerobic work capacity of the patients was also determined.

RESULTS

The MHC composition for I, IIA and IIX isoforms was found to be 35.3% +/- 18.2%, 35.9% +/- 7.1% and 28.9% +/- 15.6%, respectively, findings supported by the ATPase histochemically determined fibre-type composition of the vastus lateralis muscle. The mean fibre area of type 1 and 2 fibres was 3283 +/- 873 and 3594 +/- 1483 MICROm2, respectively. The MHC composition and the size of the type 1 fibres of the patients on HD were significantly different from those of the control subjects.

CONCLUSIONS

The data demonstrate relatively fewer type 1 and consequently more type 2x fibres, with a corresponding change in MHC isoforms (MHC I and MHC IIX) in the skeletal muscle of patients on HD. Several patients on HD were found to have <15% type 1 (or relative percentage of MHC I) fibres. Such a low percentage of type 1 fibres is very rarely observed in normal untrained subjects. Chronic uraemia more severely affects the composition than the size of fibres.

Neuromuscular electrical stimulation of completely paralyzed abdominal muscles in spinal cord-injured patients: a pilot study

STUDY DESIGN

Prospective placebo-controlled.

OBJECTIVE

The effect of abdominal neuromuscular electrical stimulation (NMES) in patients with spinal cord injury. The principal parameters observed in this study are lung capacity, colonic transit, patient satisfaction of used method and of aesthetics effect on abdominal wall.

SETTINGS

Centre de Traumatologie et de Réadaptation, Brussels, Belgium.

METHODS

A total of 10 volunteers participated in this study and were assigned to two groups-the effective electrical stimulation group (ESG) and the placebo-controlled group (PG). NMES of abdominal muscles was performed 25 min per day for 8 weeks.

RESULTS

NMES significantly decreased forced vital capacity (FVC) in ESG but not in PG. In ESG, colonic transit was accelerated in ascending, transverse and descending colon but transit in rectosigmoideum was not affected. In PG, no variations in colonic transit were observed. Satisfaction scale shows a better influence on aesthetics effect in ESG than in PG.

CONCLUSION

This pilot study shows that NMES of paralyzed abdominal muscles positively affects colonic transit except in rectosigmoideum segment and negatively affects FVC. It could be a simple self-used method to regulate colonic transfer with considerably good cosmetic effect on abdominal wall. However, regular verification of FVC will probably be necessary.

Outcomes of a home cycling program using functional electrical stimulation or passive motion for children with spinal cord injury: a case series

BACKGROUND/OBJECTIVE

Children with spinal cord injury (SCI) are at risk for musculoskeletal and cardiovascular complications. Stationary cycling using functional electrical stimulation (FES) or passive motion has been suggested to address these complications. The purpose of this case series is to report the outcomes of a 6-month at-home cycling program for 4 children with SCI.

METHODS

Two children cycled with FES and 2 cycled passively at home for 1 hour, 3 times per week.

OUTCOME MEASURES

Data collected included bone mineral density of the left femoral neck, distal femur, and proximal tibia; quadriceps and hamstring muscle volume; stimulated quadriceps and hamstring muscle strength; a fasting lipid profile; and heart rate and oxygen consumption during incremental upper extremity ergometry testing.

RESULTS

The 2 children cycling with FES and 1 child cycling passively exhibited improved bone mineral density, muscle volume, stimulated quadriceps strength, and lower resting heart rate. For the second child cycling passively, few changes were realized. Overall, the lipid results were inconsistent, with some positive and some negative changes seen.

CONCLUSIONS

This case series suggests that cycling with or without FES may have positive health benefits and was a practical home exercise option for these children with SCI.

Stable muscle atrophy in long-term paraplegics with complete upper motor neuron lesion from 3- to 20-year SCI

STUDY DESIGN

Unrandomized trial.

OBJECTIVES

To investigate the structural and functional relationships and the progression of muscle atrophy up to 20 years of spastic paraplegia.

SETTING

Clinical follow-up in Vienna, Austria; muscle biopsies analyzed by light microscopy in Padova and by electron microscopy (EM) in Chieti, Italy.

METHODS

Force was measured as knee extension torque; trophism by computer tomography scan; tissue composition and fiber morphology by histopathology and EM.

RESULTS

In the long-term group of patients (17.0+/-2.6 years), force and size of thigh muscles were only slightly different from those of mid-term subjects (2.2+/-0.5 years). Histology and ultrastructure confirm that the difference in average size of muscle fibers between long-term and mid-term paralyzed leg muscles is actually very small. In addition, muscle fibers maintain the striated appearance characteristic of normal skeletal fibers even after 14-20 years of paralysis. Ultrastructural alterations of the activating and metabolic machineries, and the presence of fibers with lower motor neuron denervation features, may explain the low-force output and the reduced endurance of paretic muscles.

CONCLUSION

The stable muscle atrophy that characterizes long-lasting spastic paraplegia suggests that there are no upper-time limits to begin a training program based on functional electrical stimulation.

Functional electrical stimulation after spinal cord injury: current use, therapeutic effects and future directions

Repair of the injured spinal cord by regeneration therapy remains an elusive goal. In contrast, progress in medical care and rehabilitation has resulted in improved health and function of persons with spinal cord injury (SCI). In the absence of a cure, raising the level of achievable function in mobility and self-care will first and foremost depend on creative use of the rapidly advancing technology that has been so widely applied in our society. Building on achievements in microelectronics, microprocessing and neuroscience, rehabilitation medicine scientists have succeeded in developing functional electrical stimulation (FES) systems that enable certain individuals with SCI to use their paralyzed hands, arms, trunk, legs and diaphragm for functional purposes and gain a degree of control over bladder and bowel evacuation. This review presents an overview of the progress made, describes the current challenges and suggests ways to improve further FES systems and make these more widely available.

Cardiovascular Health and Exercise Rehabilitation in Spinal Cord Injury

There appears to be an increased prevalence and earlier onset of cardiovascular disease (CVD) in persons with SCI. Physical inactivity is thought to be a key factor in the increased risk for CVD. Physical inactivity is highly prevalent in persons with SCI and it appears that activities of daily living are not sufficient to maintain cardiovascular fitness and health. This systematic review examines the current literature regarding the risk for CVD and the effectiveness of varied exercise rehabilitation programs in attenuating the risk for CVD in SCI.

Effects of training programs for spinal cord injury

INTRODUCTION

Endurance exercise training programs in patients with spinal cord injury (SCI) were largely studied to determine different types of adaptations. The aim of specific rehabilitation is to obtain maximal gains in quality-of-life (QoL) after SCI.

OBJECTIVE

To review the literature on the efficiency of training programs for SCI.

METHODS

We searched the MEDline database with the keywords SCI, paraplegia and quadriplegia and synonyms, then combined them with one of the following terms: rehabilitation, training, exercise conditioning, physical fitness, exercise prescription, adaptation, effect, or benefit. We found 65 articles related to the physiological and psychological effects of training programmes on patients with SCI.

RESULTS AND DISCUSSION

Training programs after SCI offer reconditioning cardiorespiratory, cardiovascular, cardiac, metabolic, bone, biomechanical, muscle adaptation, and QoL benefits. Reconditioning training increases VO2 max, reverses leg vascular resistance in the paralyzed legs and has possible cardiac and neural adaptations, favorable catecholamine responses and effects on platelet aggregation. Reconditioning can also modify lipid profile, reduce risk for cardiovascular diseases, prevent osteoporosis and increase maximal upper-extremity muscle strength, sprint power output and maximal power output. This effect allows for considerable improvement in mechanical efficiency and wheelchair propulsion technique.

CONCLUSIONS

Reconditioning training programs after SCI have a direct impact on function and QoL, permitting participation in physical activities in addition to daily living activities in subjects with SCI.

Physiological roles of muscle-derived interleukin-6 in response to exercise

PURPOSE OF REVIEW

To discuss recent findings with regard to the regulation of muscle-derived interleukin-6 as well as the possible physiological and metabolic roles of interleukin-6 in response to exercise.

RECENT FINDINGS

Contraction-induced transcription and release of interleukin-6 is primarily regulated by an altered intramuscular milieu in response to exercise. Accordingly, changes in calcium homeostasis, impaired glucose availability and increased formation of reactive oxygen species are all associated with exercise and capable of activating transcription factors known to regulate interleukin-6 synthesis. Acute interleukin-6 administration to humans increases lipolysis, fat oxidation and insulin-mediated glucose disposal. Adenosine monophosphate-activated protein kinase activation by interleukin-6 appears to play an important role in modulating some of these metabolic effects. Interleukin-6 facilitates an antiinflammatory milieu and may exert some of its biological effects via inhibition of the proinflammatory cytokine tumor necrosis factor-alpha.

SUMMARY

The discovery of contracting muscle as a cytokine-producing organ opens a new paradigm: skeletal muscle is an endocrine organ that in response to contractions produces and releases 'myokines', which subsequently can modulate the metabolic and immunological response to exercise in several tissues. In our view, interleukin-6 may be one of several myokines.

Musculoskeletal adaptations in chronic spinal cord injury: effects of long-term soleus electrical stimulation training

OBJECTIVE

The purpose of this study was to determine whether long-term electrical stimulation training of the paralyzed soleus could change this muscle's physiological properties (torque, fatigue index, potentiation index, torque-time integral) and increase tibia bone mineral density.

METHODS

Four men with chronic (>2 years) complete spinal cord injury (SCI; American Spinal Injury Association classification A) trained 1 soleus muscle using an isometric plantar flexion electrical stimulation protocol. The untrained limb served as a within-subject control. The protocol involved ~ 30 minutes of training each day, 5 days a week, for a period of 6 to 11 months. Mean compliance over 11 months of training was 91% for 3 subjects. A fourth subject achieved high compliance after only 5 months of training. Mean estimated compressive loads delivered to the tibia were approximately 110% of body weight. Over the 11 months of training, the muscle plantar flexion torque, fatigue index, potentiation index, and torque-time integral were evaluated periodically. Bone mineral density (dual-energy x-ray absorptiometry) was evaluated before and after the training program.

RESULTS

The trained limb fatigue index, potentiation index, and torque-time integral showed rapid and robust training effects (P<.05). Soleus electrical stimulation training yielded no changes to the proximal tibia bone mineral density, as measured by dual-energy x-ray absorptiometry. The subject with low compliance experienced fatigue index and torque-time integral improvements only when his compliance surpassed 80%. In contrast, his potentiation index showed adaptations even when compliance was low.

CONCLUSIONS

These findings highlight the persistent adaptive capabilities of chronically paralyzed muscle but suggest that preventing musculoskeletal adaptations after SCI may be more effective than reversing changes in the chronic condition.

Beneficial health effects of exercise – the role of IL-6 as a myokine

It is not clear how contracting skeletal muscles mediate the numerous and diverse metabolic and physiological effects that are beneficial for health. Researchers have searched for a muscle-contraction-induced factor - an 'exercise factor' - that mediates some of the exercise effects in other tissues such as the liver and adipose tissue. In our search for such a factor, we encountered the cytokine interleukin (IL)-6, which is produced by contracting muscles and released into the blood. We propose that muscle-derived IL-6 meets the criteria of an exercise factor and that such classes of cytokine should be named 'myokines'. The discovery of contracting muscle as a cytokine-producing organ creates a new paradigm: skeletal muscle as an endocrine organ. By contracting, it stimulates the production and release of myokines that can influence metabolism in tissue and organs. Newly identified myokines and their receptors could serve as targets in the treatment of metabolic disorders and other diseases.

Effect of long-term muscle paralysis on human single fiber mechanics

This study compared human muscles following long-term reduced neuromuscular activity to those with normal functioning regarding single fiber properties. Biopsies were obtained from the vastus lateralis of 5 individuals with chronic (>3 yr) spinal cord injury (SCI) and 10 able-bodied controls (CTRL). Chemically skinned fibers were tested for active and passive mechanical characteristics and subsequently classified according to myosin heavy chain (MHC) content. SCI individuals had smaller proportions of type I (11 +/- 7 vs. 34 +/- 5%) and IIa fibers (11 +/- 6 vs. 31 +/- 5%), whereas type IIx fibers were more frequent (40 +/- 13 vs. 7 +/- 3%) compared with CTRL subjects (P < 0.05). Cross-sectional area and peak force were similar in both groups for all fiber types. Unloaded shortening velocity of fibers from paralyzed muscles was higher in type IIa, IIa/IIx, and IIx fibers (26, 65, and 47%, respectively; P < 0.01). Consequently, absolute peak power was greater in type IIa (46%; P < 0.05) and IIa/IIx fibers (118%; P < 0.01) of the SCI group, whereas normalized peak power was higher in type IIa/IIx fibers (71%; P < 0.001). Ca(2+) sensitivity and passive fiber characteristics were not different between the two groups in any fiber type. Composite values (average value across all fibers analyzed within each study participant) showed similar results for cross-sectional area and peak force, whereas maximal contraction velocity and fiber power were more than 100% greater in SCI individuals. These data illustrate that contractile performance is preserved or even higher in the remaining fibers of human muscles following reduced neuromuscular activity.

Rapid vascular adaptations to training and detraining in persons with spinal cord injury

OBJECTIVE

To assess the time course of arterial adaptations during 6 weeks of functional electric stimulation (FES) training and 6 weeks of detraining in subjects with spinal cord injury (SCI).

DESIGN

Intervention study (before-after trial).

SETTING

University medical center.

PARTICIPANTS

Volunteer sample of 9 subjects with SCI.

INTERVENTIONS

Six weeks of twice weekly FES cycling and 6 weeks of detraining.

MAIN OUTCOME MEASURES

Vascular characteristics were measured by plethysmography (baseline and peak blood flow of the thigh) and echo Doppler (diameter of the femoral artery and flow-mediated dilation [FMD]).

RESULTS

After 2 weeks of FES training, arterial characteristics changed significantly; there was an increase in baseline and peak blood flow, an increase in femoral artery diameter, and a decrease in FMD of the femoral artery. Detraining reversed baseline and peak thigh blood flow, vascular resistance, and femoral diameter toward pretraining values within 1 week. However, detraining did not restore the FMD of the femoral artery, even after 6 weeks.

CONCLUSIONS

Two weeks of hybrid FES training (4 exercise bouts) is sufficient to improve peak leg blood flow and arterial diameter, and to normalize FMD. In addition, detraining results in rapidly reversed vascular characteristics within 1 week.

Physiological effects of lower extremity functional electrical stimulation in early spinal cord injury: lack of efficacy to prevent bone loss

STUDY DESIGN

Controlled, repeat-measures study.

OBJECTIVES

To determine if functional electrical stimulation (FES) can affect bone atrophy in early spinal cord injury (SCI), and the safety, tolerance and feasibility of this modality in bone loss remediation.

SETTING

Spinal Injuries Units, Royal Adelaide Hospital and Hampstead Rehabilitation Centre, South Australia.

METHODS

Patients with acute SCI (ASIA A-D) were allocated to FES (n=23, 28+/-9 years, C4-T10, 13 Tetra) and control groups (CON, n=10, 31+/-11 years, C5-T12, four Tetra). The intervention group received discontinuous FES to lower limb muscles (15 min sessions to each leg twice daily, over a 5-day week, for 5 months). Dual energy X-ray absorptiometry (DEXA) measured total body bone mineral density (tbBMD), hip, spine BMD and fat mass (FM) within 3 weeks, and 3 and 6 months postinjury.

RESULTS

FES and CON groups' tbBMD differed significantly at 3 months postinjury (P<0.01), but not thereafter. Other DEXA measures (hip, spine BMD, FM) did not differ between groups at any time. No adverse events were identified.

CONCLUSION

Electrically stimulated muscle activation was elicited, and tetanic effects were reproducible; however, there were no convincing trends to suggest that FES can play a clinically relevant role in osteoporosis prevention (or subsequent fracture risk) in the recently injured patient. The lack of an osteogenic response in paralysed extremities to electrically evoked exercise during subacute and rehabilitation/recovery phases cannot be fully explained, and may warrant further evaluation.

Fatigue of muscles weakened by death of motoneurons

Weakness is a characteristic of muscles influenced by the postpolio syndrome (PPS), amyotrophic lateral sclerosis (ALS), and spinal cord injury (SCI). The strength deficits relate to changes in muscle use and to the chronic denervation that can follow the spinal motoneuron death common to these disorders. PPS, ALS, and SCI also involve variable amounts of supraspinal neuron death, the effects of which on muscle weakness remains unclear. Nevertheless, weakness of muscle itself defines the functional consequences of these disorders. A weaker muscle requires an individual to work that muscle at higher than usual intensities relative to its maximal capacity, inducing progressive fatigue and an increased sense of effort. Little evidence is available to suggest that the fatigue commonly experienced by individuals with these disorders relates to an increase in the intrinsic fatigability of the muscle fibers. The only exception is when SCI induces chronic muscle paralysis. To reduce long-term functional deficits in these disorders, studies must identify the signaling pathways that influence neuron survival and determine the factors that encourage and limit sprouting of motor axons. This may ensure that a greater proportion of the fibers in each muscle remain innervated and available for use.

Neural and muscular changes to detraining after electrostimulation training

We investigated the effects of 4 weeks of detraining subsequent to an 8-week electrostimulation (ES) training program on changes in muscle strength, neural and muscular properties of the knee extensor muscles. Nine male subjects followed the training program consisting of 32 sessions of isometric ES training over an 8-week period. All subjects were tested before and after 8 weeks of ES training, and were then retested after 4 weeks of detraining. Quadriceps muscle anatomical cross-sectional area (ACSA) was assessed by ultrasonography imaging. The electromyographic (EMG) activity and muscle activation (i.e., by means of the twitch interpolation technique) obtained during maximal voluntary contractions (MVC) were used to examine neural adaptations. After training, the knee extensor voluntary torque increased significantly by 26%. Torque gains were accompanied by an increase in vastii EMG activity normalized to respective M-wave (+43%), muscle activation (+6%) and quadriceps ACSA (+6%). After detraining, knee extensor MVC, vastii EMG activity, muscle activation and quadriceps ACSA decreased significantly by 9%, 20%, 5% and 3%, respectively. Also, the knee extensor MVC values remained significantly elevated (14%) above baseline levels at the end of the detraining period and this was associated with a larger quadriceps ACSA (+3%) but not with a higher neural activation. We concluded that the voluntary torque losses observed after detraining could be attributed to both neural and muscular alterations. Muscle size preservation could explain the higher knee extensor MVC values observed after the cessation of training compared to those obtained before training, therefore indicating that muscle size changes are slower than neural drive reduction.

Neuromuscular Adaptations to Electrostimulation Resistance Training

A combination of in vivo and in vitro analyses was performed to investigate muscular and neural adaptations of the weaker (nondominant) quadriceps femoris muscle of one healthy individual to short-term electrostimulation resistance training. The increase in maximal voluntary strength (+12%) was accompanied by neural (cross-education effect and increased muscle activation) and muscle adaptations (impairment of whole-muscle contractile properties). Significant changes in myosin heavy chain (MHC) isoforms relative content (+22% for MHC-2A and -28% for MHC-2X), single-fiber cross-sectional area (+27% for type 1 and +6% for type 2A muscle fibers), and specific tension of type 1 (+67%) but not type 2A fibers were also observed after training. Plastic changes in neural control confirm the possible involvement of both spinal and supraspinal structures to electrically evoked contractions. Changes at the single muscle fiber level induced by electrostimulation resistance training were significant and preferentially affected slow, type 1 fibers.

Musculoskeletal plasticity after acute spinal cord injury: effects of long-term neuromuscular electrical stimulation training

Maintaining the physiologic integrity of paralyzed limbs may be critical for those with spinal cord injury (SCI) to be viable candidates for a future cure. No long-term intervention has been tested to attempt to prevent the severe musculoskeletal deterioration that occurs after SCI. The purposes of this study were to determine whether a long-term neuromuscular electrical stimulation training program can preserve the physiological properties of the plantar flexor muscles (peak torque, fatigue index, torque-time integral, and contractile speed) as well as influence distal tibia trabecular bone mineral density (BMD). Subjects began unilateral plantar flexion electrical stimulation training within 6 wk after SCI while the untrained leg served as a control. Mean compliance for the 2-yr training program was 83%. Mean estimated compressive loads delivered to the tibia were approximately 1-1.5 times body weight. The training protocol yielded significant trained versus untrained limb differences for torque (+24%), torque-time integral (+27%), fatigue index (+50%), torque rise time (+45%), and between-twitch fusion (+15%). These between-limb differences were even greater when measured at the end of a repetitive stimulation protocol (125 contractions). Peripheral quantitative computed tomography revealed 31% higher distal tibia trabecular BMD in trained limbs than in untrained limbs. The intervention used in this study was sufficient to limit many of the deleterious muscular and skeletal adaptations that normally occur after SCI. Importantly, this method of load delivery was feasible and may serve as the basis for an intervention to preserve the musculoskeletal properties of individuals with SCI.

Improvement of Metabolic and Cardiorespiratory Responses Through Treadmill Gait Training With Neuromuscular Electrical Stimulation in Quadriplegic Subjects

This work assessed the influence of treadmill gait training with neuromuscular electrical stimulation (NMES) on the metabolic and cardiorespiratory responses in quadriplegic subjects. The gait group (GG) (n=11) performed 6 months of treadmill training with 30-50% body weight support and with the help of physiotherapists, twice a week, allotting 20 min for each session. The control group (CG) (n=10), during the 6 months of training, did not perform any activity using NMES, performing instead conventional physiotherapy. Metabolic and cardiorespiratory responses (O(2) uptake [VO(2)], CO(2) production [VCO(2)], pulmonary ventilation (V(E)), heart rate [HR], and blood pressure [BP]) were measured on inclusion and after 6 months. For the GG, differences were found in all parameters after training (P<0.05), except for HR and diastolic BP. During gait, VO(2) (L/min) increased by 36%, VCO(2) (L/min) increased by 42.97%, V(E) (L/min) increased by 30.48%, and systolic BP (mm Hg) increased by 4.8%. For the CG, only VO(2) and VCO(2) (L/min) significantly increased at rest (30.82 and 16.39%, respectively) and during knee-extension exercise (26.29 and 17.37%, respectively). Treadmill gait with NMES was, therefore, more efficient toward increasing the aerobic capacity due to yielding higher metabolic and cardiovascular stresses.

Energy well spent fighting the diabetes epidemic

As the global burden of type 2 diabetes increases, medical science races to comprehensively understand its molecular aetiology. We suggest that the apparent struggle to seek a pharmacological or molecular victory to the diabetes epidemic is a flawed strategy given that evolution has already provided us with the best medicine. Recent molecular evidence highlights the interaction between muscle fatty acid kinetics in dictating whole body insulin action. Insights from an evolutionary perspective suggest that the ability of the body to evoke insulin resistance and store energy as fat within muscle cells is a normal physiological response to aid our survival during food or carbohydrate scarcity, but this 'hunter-gatherer physiology' predisposes to diabetes in a modern environment characterized by ample food availability and muscle inactivity. We contend that the true value of physical activity in the prevention and treatment of insulin resistance has been missed by the medical community because scientific investigation has been constructed upon physical activity recommendations that were never intended for this purpose. These recommendations provide a level of metabolic stress insufficient to be compatible with the expectations of our genes.

Investigação das alterações osteo-metabólicas e cardio-respiratórias ocorridas após o treinamento de marcha sob estimulação elétrica neuromuscular em pacientes tetraplégicos

Este trabalho objetivou avaliar o efeito do treinamento de marcha, com estimulação elétrica neuromuscular (EENM), nos sistemas esquelético e cardio-respiratório de tetraplégicos (C4-C8) completos. Consumo de oxigênio (VO2), produção de dióxido de carbono (VCO2), ventilação minuto (VE), freqüência cardíaca (FC), pressão arterial (PA), gasto energético, análise de marcadores ósseos (osteocalcina, fosfatase alcalina óssea, piridinolina e deoxipiridinolina) e densitometria óssea (DEXA) do colo femoral e fêmur total foram realizados no início e após seis meses. Onze pacientes realizaram marcha sobre esteira ergométrica, com EENM e descarga entre 60-70% do peso corporal, durante seis meses, duas vezes semanais, vinte minutos diários. Dez pacientes não realizaram marcha. No grupo de marcha, 81,8% apresentaram aumentos significativos nos marcadores de formação, dos quais 72,7% também apresentaram diminuição da reabsorção óssea. No grupo controle, 20% apresentaram aumento na formação óssea. Os resultados da DEXA foram, em geral, opostos àqueles dos marcadores ósseos. Os testes cardio-respiratórios mostraram um aumento significativo para VO2 l/min (36%), VCO2 (42,97%), VE (30,48%), PAS mmHg (4,8%) e gasto energético kcal/min (37,68%). No grupo controle, apenas o VO2 l/min aumentou significativamente (26,29%). O treinamento de marcha com EENM foi mais eficiente para aumentar a taxa de formação óssea e a capacidade aeróbica dos tetraplégicos.

The effect of body weight-supported treadmill training on muscle morphology in an individual with chronic, motor-complete spinal cord injury: A case study

OBJECTIVE

The purpose of this pilot study was to examine the effects of 4 months of thrice-weekly body weight-supported treadmill training (BWSTT) on skeletal muscle morphology in a woman (age 27 y) with chronic, motor-complete (ASIA B) spinal cord injury (SCI).

METHODS

The participant performed passive thrice-weekly BWSTT for 4 months (48 total sessions) with manual assistance from therapists. Muscle biopsies of the vastus lateralis were taken prior to the beginning of the training program as well as following the completion of 4 months of training. Histochemical analysis was utilized to evaluate changes in muscle fiber size and type following training.

RESULTS

At baseline, vastus lateralis muscle biopsies showed evidence of fiber atrophy and fiber type redistribution typical of persons with SCI, with mean fiber areas (and % distributions) of type I, type IIa and type IIx fibers being 3474 microm2 (1.3%), 3146 microm2 (30.8%) and 1284 microm2 (68.0%), respectively. Following training, there were increases in treadmill walking speed (pre: 1.0km/h; post: 2.5km/h) and distance walked/session (pre: 500m; post: 1875m). Vastus lateralis mean fiber area increased by 27.1% and type I fiber % distribution increased to 24.6%, whereas type IIa and type IIx fiber % distributions both decreased following training.

CONCLUSION

These data indicate that 4 months of thrice-weekly BWSTT improved muscle morphology in an individual with chronic, motor-complete SCI.

Bone loss and muscle atrophy in spinal cord injury: epidemiology, fracture prediction, and rehabilitation strategies

Individuals with spinal cord injury (SCI) often experience bone loss and muscle atrophy. Muscle atrophy can result in reduced metabolic rate and increase the risk of metabolic disorders. Sublesional osteoporosis predisposes individuals with SCI to an increased risk of low-trauma fracture. Fractures in people with SCI have been reported during transfers from bed to chair, and while being turned in bed. The bone loss and muscle atrophy that occur after SCI are substantial and may be influenced by factors such as completeness of injury or time postinjury. A number of interventions, including standing, electrically stimulated cycling or resistance training, and walking exercises have been explored with the aim of reducing bone loss and/or increasing bone mass and muscle mass in individuals with SCI. Exercise with electrical stimulation appears to increase muscle mass and/or prevent atrophy, but studies investigating its effect on bone are conflicting. Several methodological limitations in exercise studies with individuals with SCI to date limit our ability to confirm the utility of exercise for improving skeletal status. The impact of standing or walking exercises on muscle and bone has not been well established. Future research should carefully consider the study design, skeletal measurement sites, and the measurement techniques used in order to facilitate sound conclusions.

Comparison of stimulation patterns for FES-cycling using measures of oxygen cost and stimulation cost

AIM

The energy efficiency of FES-cycling in spinal cord injured subjects is very much lower than that of normal cycling, and efficiency is dependent upon the parameters of muscle stimulation. We investigated measures which can be used to evaluate the effect on cycling performance of changes in stimulation parameters, and which might therefore be used to optimise them. We aimed to determine whether oxygen cost and stimulation cost measurements are sensitive enough to allow discrimination between the efficacy of different activation ranges for stimulation of each muscle group during constant-power cycling.

METHODS

We employed a custom FES-cycling ergometer system, with accurate control of cadence and stimulated exercise workrate. Two sets of muscle activation angles ("stimulation patterns"), denoted "P1" and "P2", were applied repeatedly (eight times each) during constant-power cycling, in a repeated measures design with a single paraplegic subject. Pulmonary oxygen uptake was measured in real time and used to determine the oxygen cost of the exercise. A new measure of stimulation cost of the exercise is proposed, which represents the total rate of stimulation charge applied to the stimulated muscle groups during cycling. A number of energy-efficiency measures were also estimated.

RESULTS

Average oxygen cost and stimulation cost of P1 were found to be significantly lower than those for P2 (paired t-test, p<0.05): oxygen costs were 0.56+/-0.03l min-1 and 0.61+/-0.04l min-1 (mean+/-S.D.), respectively; stimulation costs were 74.91+/-12.15 mC min-1 and 100.30+/-14.78 mC min-1 (mean+/-S.D.), respectively. Correspondingly, all efficiency estimates for P1 were greater than those for P2.

CONCLUSION

Oxygen cost and stimulation cost measures both allow discrimination between the efficacy of different muscle activation patterns during constant-power FES-cycling. However, stimulation cost is more easily determined in real time, and responds more rapidly and with greatly improved signal-to-noise properties than the ventilatory oxygen uptake measurements required for estimation of oxygen cost. These measures may find utility in the adjustment of stimulation patterns for achievement of optimal cycling performance.

Application of Animal Models: Chronic Electrical Stimulation-Induced Contractile Activity

Unilateral, chronic low-frequency electrical stimulation (CLFS) is an experimental model that evokes numerous biochemical and physiological adaptations in skeletal muscle. These occur within a short time frame and are restricted to the stimulated muscle. The humoral effects of whole body exercise are eliminated and the nonstimulated contralaterai limb can often be used as a control muscle, if possible effects on the contralateral side are considered. CLFS induces a fast-to-slow transformation of muscle because of alterations in calcium dynamics and myofibrillar proteins, and a white-to-red transformation because of changes in mitochondrial enzymes, myoglobin, and the induction of angiogenesis. These adaptations occur in a coordinated time-dependent manner and result from altered gene expression, including transcriptional and posttranscriptional processes. CLFS techniques have also been applied to myocytes in cell culture, which provide a greater opportunity for the delivery of pharmacological agents or for the application of gene transfer methodologies. Clinical applications of the CLFS technique have been limited, but they have shown potential therapeutic value in patients in whom voluntary muscle contraction is not possible due to debilitating disease and/or injury. Thus the CLFS technique has great value for studying various aspects of muscle adaptation, and its wider scientific application to a variety of neuromuscular-based disorders in humans appears to be warranted. Key words: skeletal muscle, muscle plasticity, endurance training, mitochondrial biogenesis, fiber types

Changes in skeletal muscle size and glucose tolerance with electrically stimulated resistance training in subjects with chronic spinal cord injury

OBJECTIVE

To determine the effect of residence-based, resistance exercise training (RET) on affected skeletal muscle size and glucose tolerance after long-standing, complete spinal cord injury (SCI).

DESIGN

Before-after trial.

SETTING

University laboratory trial.

PARTICIPANTS

Five men with chronic, complete SCI (C5-T9).

INTERVENTION

Magnetic resonance images of the thighs and an oral glucose tolerance test were performed before and after RET. Subjects performed RET with both thighs, 2 d/wk for 4 sets of 10 unilateral, dynamic knee extensions for 12 weeks. Neuromuscular electric stimulation induced RET by activating the knee extensors.

MAIN OUTCOME MEASURES

Quadriceps femoris muscle cross-sectional area (CSA), plasma glucose, and insulin concentrations were measured before and after RET. Results Skeletal muscle CSA increased by 35% in the right quadriceps femoris (from 32.6 cm2 to 44.0 cm2) and by 39% in the left quadriceps femoris (from 34.6 cm2 to 47.9 cm2) as a result of training (P < .05). There were no significant changes in blood glucose or insulin after training. However, a trend for a reduction in plasma glucose levels was observed (P = .074). Conclusions Affected skeletal muscle can achieve substantial hypertrophy years after SCI with resistance exercise. Furthermore, our results suggest that this type of training may enhance glucose disposal.

Response of the arterial blood pressure of quadriplegic patients to treadmill gait training

Blood pressure pattern was analyzed in 12 complete quadriplegics with chronic lesions after three months of treadmill gait training. Before training, blood pressure values were obtained at rest, during treadmill walking and during the recovery phase. Gait training was performed for 20 min twice a week for three months. Treadmill gait was achieved using neuromuscular electrical stimulation, assisted by partial body weight relief (30-50%). After training, blood pressure was evaluated at rest, during gait and during recovery phase. Before and after training, mean systolic blood pressures and heart rates increased significantly during gait compared to rest (94.16 +/- 5.15 to 105 +/- 5.22 mmHg and 74.27 +/- 10.09 to 106.23 +/- 17.31 bpm, respectively), and blood pressure decreased significantly in the recovery phase (86.66 +/- 9.84 and 57.5 +/- 8.66 mmHg, respectively). After three months of training, systolic blood pressure became higher at rest (94.16 +/- 5.15 mmHg before training and 100 +/- 8.52 mmHg after training; P < 0.05) and during gait exercise (105 +/- 5.22 mmHg before and 110 +/- 7.38 mmHg after training; P < 0.05) when compared to the initial values, with no changes in heart rate. No changes occurred in blood pressure during the recovery phase, with the lower values being maintained. A drop in systolic pressure from 105 +/- 5.22 to 86.66 +/- 9.84 mmHg before training and from 110 +/- 7.38 to 90 +/- 7.38 mmHg after training was noticed immediately after exercise, thus resulting in hypotensive symptoms when chronic quadriplegics reach the sitting position from the upright position.

Local Vascular Adaptations after Hybrid Training in Spinal Cord–Injured Subjects

PURPOSE

Studies investigating vascular adaptations in non-exercised areas during whole body exercise training show conflicting results. Individuals with spinal cord injury (SCI) provide a unique model to examine vascular adaptations in active tissue vs adjacent inactive areas. The purpose of this study is to assess the effects of 4 wk of voluntary arm and electrically stimulated leg exercise (8-12 sessions) on vascular adaptations in active areas (thigh and arms) and inactive areas (calf).

METHODS

Vascular characteristics were measured by plethysmography (blood flow and vascular resistance) and echo Doppler (diameter and flow-mediated dilation (FMD) after 13 min of ischemia).

RESULTS

After training, increased thigh baseline and peak blood flow, decreased thigh baseline vascular resistance, and increased diameter of the common femoral artery were found in the stimulated thigh tissue. Forearm and calf arterial parameters and FMD, in both superficial femoral artery and brachial artery, did not change. The lack of activity in the calf and concomitant insufficient elevation of blood flow during training, and the high initial training status of the arms are suggested to explain the absence of vascular adaptations in these areas.

CONCLUSION

The presence of vascular adaptations after only 4 wk of FES cycling indicates that adaptations occur in an early phase. In addition, 4 wk of whole body exercise training in SCI individuals leads to vascular adaptations in the exercised tissues (thigh) but not in nonstimulated passive tissue (calf).

Energy expenditure during rest and treadmill gait training in quadriplegic subjects

STUDY DESIGN

The analysis of oxygen uptake (VO(2)) and energy consumption in quadriplegics after 6 months of treadmill gait with neuromuscular electrical stimulation (NMES).

OBJECTIVES

To compare metabolic responses in quadriplegics after 6 months of treadmill training, with NMES (30-50% body weight relief), with quadriplegics who did not perform gait.

SETTING

Ambulatory of University Hospital, Brazil.

METHODS

Quadriplegics were separated into gait and control groups (CGs). On inclusion, all subjects performed VO(2) test. In the gait group (GG) (n=11), the protocol consisted of 8 min of rest, 10 min of treadmill walking using NMES and 10 min of recovery. In the CG (n=10), testing consisted of 8 min rest, 15 min of quadriceps endurance exercise in sitting position with NMES and 10 min recovery. VO(2), carbon dioxide production (VCO(2)) and energy consumption were measured. The GG performed 6 months of treadmill training, using NMES, for 20 min, twice a week. The CG did not practice any activity with NMES, performing conventional physiotherapy only; the CG was stimulated only during the cardiorespiratory test.

RESULTS

All parameters increased significantly for the GG: 36% for VO(2) (l/min), 43% for VCO(2) (l/min) and 32.5% for energy consumption (J/kg/s). For the CG, during knee extension exercise, VO(2) increased without changes in the energy consumption (P<0.05); smaller values were obtained for all parameters when compared to those obtained during gait.

CONCLUSIONS

Quadriplegic gait was efficient towards increasing VO(2) and energy consumption, which can decrease the risk of cardiovascular diseases.

Mathematical models use varying parameter strategies to represent paralyzed muscle force properties: a sensitivity analysis

Background

Mathematical muscle models may be useful for the determination of appropriate musculoskeletal stresses that will safely maintain the integrity of muscle and bone following spinal cord injury. Several models have been proposed to represent paralyzed muscle, but there have not been any systematic comparisons of modelling approaches to better understand the relationships between model parameters and muscle contractile properties. This sensitivity analysis of simulated muscle forces using three currently available mathematical models provides insight into the differences in modelling strategies as well as any direct parameter associations with simulated muscle force properties.

Methods

Three mathematical muscle models were compared: a traditional linear model with 3 parameters and two contemporary nonlinear models each with 6 parameters. Simulated muscle forces were calculated for two stimulation patterns (constant frequency and initial doublet trains) at three frequencies (5, 10, and 20 Hz). A sensitivity analysis of each model was performed by altering a single parameter through a range of 8 values, while the remaining parameters were kept at baseline values. Specific simulated force characteristics were determined for each stimulation pattern and each parameter increment. Significant parameter influences for each simulated force property were determined using ANOVA and Tukey's follow-up tests (α ≤ 0.05), and compared to previously reported parameter definitions.

Results

Each of the 3 linear model's parameters most clearly influence either simulated force magnitude or speed properties, consistent with previous parameter definitions. The nonlinear models' parameters displayed greater redundancy between force magnitude and speed properties. Further, previous parameter definitions for one of the nonlinear models were consistently supported, while the other was only partially supported by this analysis.

Conclusion

These three mathematical models use substantially different strategies to represent simulated muscle force. The two contemporary nonlinear models' parameters have the least distinct associations with simulated muscle force properties, and the greatest parameter role redundancy compared to the traditional linear model.

Kinematic analyses of semireclined leg cycling in able-bodied and spinal cord injured individuals

STUDY DESIGN

Retrospective descriptive study.

OBJECTIVES

To evaluate the leg kinematics and motion characteristics within able-bodied (AB) and spinal cord injured (SCI) individuals during stationary semireclined cycling.

SETTING

Functional Performance Laboratory, Connecticut, USA.

METHODS

Three SCI and three AB subjects participated in steady-state leg pedaling (50 revolutions per minute). The SCI group participated in electrical stimulation (FES)-induced cycling at resistances of 0, 6.25, and 12.5 Watts (W). The AB group cycled on the same ergometer without FES at resistances of 0, 60, and 120 W. Motion capture analysis recorded joint angular position, velocity, and acceleration at hip, knee, and ankle. Joint kinematics of hip, knee, and ankle were measured during steady-state leg cycling and comparisons were made between AB and SCI subjects as resistance proportionally and relatively increased.

RESULTS

Intrasubject hip and knee movement patterns showed minimal variability across resistance levels. Comparisons between AB and SCI subjects showed that the hip and knee kinematics were very similar at all resistance levels. However, ankle movement patterns appeared to increase in variability (increased dorsiflexion) with increased resistance level in AB subjects and less so with SCI subjects. Overall, the ankle kinematics for AB and SCI subjects were dissimilar at resistance levels greater than zero.

CONCLUSIONS

The joint kinematics of the hip, knee, and ankle were found to be periodic, but the differences in ankle kinematics in AB and SCI subjects suggest more emphasise should be placed on the current design of the bike-pedal and subject-specific seat configurations.

Body-weight-support treadmill training improves blood glucose regulation in persons with incomplete spinal cord injury

The impact of a 6-mo body-weight-supported treadmill training program on glucose homeostasis and muscle metabolic characteristics was investigated. Nine individuals (31 ± 3 yr, 8.1 ± 2.5 yr postinjury; means ± SE) with incomplete spinal cord injury trained three times weekly for a total of 6 mo. Training session duration and intensity (velocity) increased by 54 ± 10% ( P < 0.01) and 135 ± 20%, respectively. Muscle biopsies and a modified glucose tolerance test (100 g glucose with [U-13C]glucose) were performed before (Pre) and after training (Post). Training resulted in a reduction in area under the curve of glucose × time (−15 ± 4%) and insulin × time (−33 ± 8%; both P < 0.05). Oxidation of exogenous (ingested) glucose increased as a result of training (Pre = 4.4 ± 0.7 g/h, Post = 7.4 ± 0.6 g/h; P < 0.05), as did oxidation of endogenous (liver) glucose (Pre = 3.8 ± 0.3 g/h, Post = 5.2 ± 0.3 g/h; P < 0.05). Training resulted in increased muscle glycogen (80 ± 23%; P < 0.05) and GLUT-4 content and hexokinase II enzyme activity (126 ± 34 and 49 ± 4%, respectively, both P < 0.01). Resting muscle phosphocreatine content also increased after training (Pre = 62.1 ± 4.3, Post = 78.7 ± 3.8, both mmol/kg dry wt and P < 0.05). Six months of thrice-weekly body-weight-supported treadmill training in persons with an incomplete spinal cord injury improved blood glucose regulation by increasing oxidation and storage of an oral glucose load. Increases in the capacity for transport and phosphorylation glucose in skeletal muscle likely play a role in these adaptations.

Neuromuscular rehabilitation by treadmill running or electrical stimulation after peripheral nerve injury and repair

Numerous studies have been devoted to the regeneration of the motor pathway toward a denervated muscle after nerve injury. However, the regeneration of sensory muscle endings after repair by self-anastomosis are little studied. In previous electrophysiological studies, our laboratory showed that the functional characteristics of tibialis anterior muscle afferents are differentially affected after injury and repair of the peroneal nerve with and without chronic electrostimulation. The present study focuses on the axonal regeneration of mechano- (fibers I and II) and metabosensitive (fibers III and IV) muscle afferents by evaluating the recovery of their response to different test agents after nerve injury and repair by self-anastomosis during 10 wk of treadmill running (LSR). Data were compared with control animals (C), animals with nerve lesion and suture (LS), and animals with lesion, suture, and chronic muscle rehabilitation by electrostimulation (LSE) with a biphasic current modulated in pulse duration and frequency, eliciting a pattern mimicking the activity delivered by the nerve to the muscle. Compared with the C group, results indicated that 1) muscle weight was smaller in LS and LSR groups, 2) the fatigue index was greater in the LS group and smaller in the LSE group, 3) metabosensibility remained altered in the LS and LSE groups, and 4) mechanosensitivity presented a large increase of the activation pattern in the LS and LSE groups. Our data indicated that chronic muscle electrostimulation partially favors the recovery of muscle properties (i.e., muscle weight and twitch response were close to the C group) and that rehabilitation by treadmill running also efficiently induced a better functional muscle afferent recovery (i.e., the discharge pattern was similar to the C group). The effectiveness of the chronic electromyostimulation and the treadmill exercise on afferent recovery is discussed with regard to parameters listed above.

Effect of load during electrical stimulation training in spinal cord injury

Electrical stimulation training is known to alter skeletal muscle characteristics after a spinal cord injury, but the effect of load on optimizing the training protocol has not been fully investigated. This study investigated two electrical-stimulation training regimes with different loads on intramuscular parameters of the paralyzed lower limbs. Six paraplegic individuals with a spinal cord injury underwent electrical stimulation training (45 min daily for 3 days per week for 10 weeks). One leg was trained statically with load, and the contralateral leg was trained dynamically with minimal load. Isometric force assessed with 35-HZ stimuli increased significantly in both legs from baseline, with the static-trained leg also being significantly higher than the dynamic-trained leg. The vastus lateralis muscle of the statically trained leg showed a significant increase in type I fibers, fiber cross-sectional area, capillary-to-fiber ratio, and citrate synthase activity when compared to both baseline and the dynamically trained leg. Relative oxygenation of the vastus lateralis muscle as determined by near infrared spectroscopy was also significantly greater after static training. This study indicates that the load that is applied to paralyzed muscle during an electrical stimulation training program is an important factor in determining the amount of muscle adaptation that can be achieved.

Increased blood pressure can reduce fatigue of thenar muscles paralyzed after spinal cord injury

The aim of this study was to evaluate whether increases in blood pressure, and presumably muscle perfusion pressure, improve the endurance of thenar muscles paralyzed chronically by cervical spinal cord injury (SCI). Resting mean arterial pressure (MAP) was low in all eight subjects (64 +/- 2 mmHg). Muscle fatigue (force decline) was produced on 2 days by intermittent supramaximal electrical stimulation of the median nerve at 20 Hz for 2 min. During one of the fatigue tests, a concurrent sustained voluntary contraction of the contralateral elbow flexors was used to increase resting MAP (by 22%, on average). Although this change in blood pressure resulted in no significant change in mean fatigue for the group, changes in MAP with exercise (median nerve stimulation with and without voluntary contraction) correlated with changes in thenar muscle fatigue in seven subjects. For every 10% increase in MAP, fatigue was reduced by approximately 3%. The data suggest that low blood pressure after chronic cervical SCI and poor blood pressure control during exercise exacerbate the fatigability of paralyzed muscles.

Treadmill training-induced adaptations in muscle phenotype in persons with incomplete spinal cord injury

Body weight-supported treadmill (BWST) training has been shown to improve ambulatory capacity in persons with a spinal cord injury (SCI); however, the effect that BWST training has on skeletal muscle phenotype is unknown. We aimed to determine whether 6 months (three sessions/week) of BWST training in neurologically stable persons with a traumatic spinal cord injury (ASIA C) alters skeletal muscle phenotype, ambulatory capacity, and blood lipid profile. Externally supported body weight decreased, and walking velocity and duration of the training sessions increased (all P < 0.05) as a result of training. Muscle biopsies revealed increases in the mean muscle-fiber area of type I and IIa fibers. Training induced a reduction in type IIax/IIx fibers, as well as a decrease in IIX myosin heavy chain, and an increase in type IIa fibers. Maximal citrate synthase and 3-hydroxy-acyl-CoA dehydrogenase activity also increased following training. BWST training brought about reductions in plasma total (-11%) and low-density lipoprotein (-13%) cholesterol. We conclude that, in patients with a spinal cord injury, BWST training is able to induce an increase in muscle fiber size and bring about increases in muscle oxidative capacity. In addition, BWST training can bring about improvements in ambulatory capacity and antiatherogenic changes in blood lipid profile.

Searching for the exercise factor: is IL-6 a candidate?

For years the search for the stimulus that initiates and maintains the change of excitability or sensibility of the regulating centers in exercise has been progressing. For lack of more precise knowledge, it has been called the 'work stimulus', 'the work factor' or 'the exercise factor'. In other terms, one big challenge for muscle and exercise physiologists has been to determine how muscles signal to central and peripheral organs. Here we discuss the possibility that interleukin-6 (IL-6) could mediate some of the health beneficial effects of exercise. In resting muscle, the IL-6 gene is silent, but it is rapidly activated by contractions. The transcription rate is very fast and the fold changes of IL-6 mRNA is marked. IL-6 is released from working muscles into the circulation in high amounts. The IL-6 production is modulated by the glycogen content in muscles, and IL-6 thus works as an energy sensor. IL-6 exerts its effect on adipose tissue, inducing lipolysis and gene transcription in abdominal subcutaneous fat and increases whole body lipid oxidation. Furthermore, IL-6 inhibits low-grade TNF-alpha-production and may thereby inhibit TNF-alpha-induced insulin resistance and atherosclerosis development. We propose that IL-6 and other cytokines, which are produced and released by skeletal muscles, exerting their effects in other organs of the body, should be named 'myokines'.

Exercise-induced gene expression in soleus muscle is dependent on time after spinal cord injury in rats

Cycling exercise attenuates atrophy in hindlimb muscles and causes changes in spinal cord properties after spinal cord injury in rats. We hypothesized that exercising soleus muscle expresses genes that are potentially beneficial to the injured spinal cord. Rats underwent spinal cord injury at T10 and were exercised on a motor-driven bicycle. Soleus muscle and lumbar spinal cord tissue were used for messenger RNA (mRNA) analysis. Gene expression of brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) was elevated 11- and 14-fold, respectively, in soleus muscle after one bout of exercise performed 5 days after spinal cord transection. Also, c-fos and heat shock protein-27 (HSP27) mRNA abundance were increased 11- and 7-fold, respectively. When exercise was started 2 days after the injury, the changes in gene expression were not observed. By contrast, at 2 but not at 5 days after transection, expression of the HSP27 gene was elevated sixfold in the lumbar spinal cord, independent of exercise. Electromyographic activity in soleus muscles was also decreased at 2 days, indicating that the spinal cord was less permissive to exercise at this early time. Long-term exercise for 4 weeks attenuated muscle atrophy equally well in rats started at 2 days or 5 days after injury. We conclude that BDNF and GDNF released from exercising muscle may be involved in exercise-induced plasticity of the spinal cord. Furthermore, the data suggest that the lumbar spinal cord undergoes time-dependent changes that temporarily impede the ability of the muscle to respond to exercise.

Molecular basis of skeletal muscle plasticity--from gene to form and function

Skeletal muscle shows an enormous plasticity to adapt to stimuli such as contractile activity (endurance exercise, electrical stimulation, denervation), loading conditions (resistance training, microgravity), substrate supply (nutritional interventions) or environmental factors (hypoxia). The presented data show that adaptive structural events occur in both muscle fibres (myofibrils, mitochondria) and associated structures (motoneurons and capillaries). Functional adaptations appear to involve alterations in regulatory mechanisms (neuronal, endocrine and intracellular signalling), contractile properties and metabolic capacities. With the appropriate molecular techniques it has been demonstrated over the past 10 years that rapid changes in skeletal muscle mRNA expression occur with exercise in human and rodent species. Recently, gene expression profiling analysis has demonstrated that transcriptional adaptations in skeletal muscle due to changes in loading involve a broad range of genes and that mRNA changes often run parallel for genes in the same functional categories. These changes can be matched to the structural/functional adaptations known to occur with corresponding stimuli. Several signalling pathways involving cytoplasmic protein kinases and nuclear-encoded transcription factors are recognized as potential master regulators that transduce physiological stress into transcriptional adaptations of batteries of metabolic and contractile genes. Nuclear reprogramming is recognized as an important event in muscle plasticity and may be related to the adaptations in the myosin type, protein turnover, and the cytoplasma-to-myonucleus ratio. The accessibility of muscle tissue to biopsies in conjunction with the advent of high-throughput gene expression analysis technology points to skeletal muscle plasticity as a particularly useful paradigm for studying gene regulatory phenomena in humans.

Acute molecular responses of skeletal muscle to resistance exercise in able-bodied and spinal cord-injured subjects

Spinal cord injury (SCI) results in muscle atrophy, which contributes to a number of health problems, such as cardiovascular deconditioning, metabolic derangement, and osteoporosis. Electromyostimulation (EMS) holds the promise of ameliorating SCI-related muscle atrophy and, therefore, improving general health. To date, EMS training of long-term SCI subjects has resulted in some muscle hypertrophy but has fallen short of normalizing muscle mass. The aim of this study was to compare the molecular responses of vastus lateralis muscles from able-bodied (AB) and SCI subjects after acute bouts of EMS-induced resistance exercise to determine whether SCI muscles displayed some impairment in response. Analysis included mRNA markers known to be responsive to increased loading in rodent muscles. Muscles of AB and SCI subjects were subjected to EMS-stimulated exercise in two 30-min bouts, separated by a 48-h rest. Needle biopsy samples were obtained 24 h after the second exercise bout. In both the AB and SCI muscles, significant changes were seen in insulin-like growth factor binding proteins 4 and 5, cyclin-dependent kinase inhibitor p21, and myogenin mRNA levels. In AB subjects, the mRNA for mechano-growth factor was also increased. Before exercise, the total RNA concentration of the SCI muscles was less than that of the AB subjects but not different postexercise. The results of this study indicate that acute bouts of resistance exercise stimulate molecular responses in the skeletal muscles of both AB and SCI subjects. The responses seen in the SCI muscles indicate that the systems that regulate these molecular responses are intact, even after extended periods of muscle unloading.

Cardiovascular control during exercise: insights from spinal cord-injured humans

BACKGROUND

We studied the role of the central nervous system, neural feedback from contracting skeletal muscles, and sympathetic activity to the heart in the control of heart rate and blood pressure during 2 levels of dynamic exercise.

METHODS AND RESULTS

Spinal cord-injured individuals (SCI) with (paraplegia, n=4) or without (tetraplegia, n=6) sympathetic innervation to the heart performed electrically induced exercise. Responses were compared with those established by able-bodied individuals (control, n=6) performing voluntary exercise at a similar pulmonary oxygen uptake. In all subjects, cardiac output and leg blood flow increased, but in SCI they reached a maximal value. The increase in cardiac output was mainly elicited by an increase in stroke volume in individuals with tetraplegia, whereas in individuals with paraplegia it was by heart rate. The increase in SCI was slow compared with that in controls. During exercise, blood pressure was stable in controls, whereas it decreased over time in SCI and especially in individuals with tetraplegia.

CONCLUSIONS

The autonomic nervous system provides for acceleration of the heart at the onset of exercise, but a slow increase in heart rate is established even without central command, neural feedback from working muscles, or autonomic influence on the heart. Yet an intact autonomic nervous system is a prerequisite for a large rise in cardiac output and in turn leg blood flow during exercise. Thus, when the sympathetic nervous system is injured at a level where it influences the heart, vasodilatation in working muscles challenges blood pressure.

Fatigue of paralyzed and control thenar muscles induced by variable or constant frequency stimulation

Muscles paralyzed by chronic (>1 yr) spinal cord injury fatigue readily. Our aim was to evaluate whether the fatigability of paralyzed thenar muscles (n = 10) could be reduced by the repeated delivery of variable versus constant frequency pulse trains. Fatigue was induced in four ways. Intermittent supramaximal median nerve stimulation (300-ms-duration trains) was delivered at 1) constant high frequency (13 pulses at 40 Hz each second for 2 min); 2) variable high frequency (each second for 2 min). The first two intervals of each variable frequency train were 5 and 20 ms. The remaining pulses were evenly distributed in time across 275 ms. The number of pulses varied for each subject such that the force time integral in the unfatigued state matched that evoked by a constant 40-Hz train; 3) constant low frequency (7 pulses at 20 Hz each second for 4 min); and 4) variable low frequency (each second for 4 min). The pulse pattern was the same as that for variable high frequency except that the force-time integral was matched to that produced by the constant low-frequency stimulation. These same experiments were performed on the thenar muscles of five able-bodied control subjects. The variable high-frequency trains used to fatigue paralyzed and control muscles had an average (+/- SE) of 12 +/- 2 and 10 +/- 1 pulses, respectively. Variable low-frequency trains had 7 +/- 1 and 6 +/- 1 pulses, respectively. Significant mean force declines of comparable magnitude (to 20-25% initial fatigue force or to 13-21% initial 50 Hz force) were seen in paralyzed muscles with all four stimulation protocols. The force reductions in paralyzed muscles were always accompanied by significant increases in half-relaxation time and decreases in force-time integral, irrespective of the stimulation protocol. Significant force decreases also occurred in control muscles during each fatigue test. Again, these force declines were similar whether constant or variable pulse patterns were used at high or low frequencies (to 40-60% initial fatigue force or to 29-36% initial 50 Hz force). The force reductions in control muscles were significantly less than those seen in paralyzed muscles, except when constant high-frequency stimulation was used. The variations in stimulation frequency, pulse pattern, and pulse number used in this study therefore had little influence on thenar muscle fatigue in control subjects or in spinal cord-injured subjects with chronic paralysis.

Effect of training on contractile and metabolic properties of wrist extensors in spinal cord-injured individuals

Paretic human muscle rapidly loses strength and oxidative endurance, and electrical stimulation training may partly reverse this. We evaluated the effects of two training protocols on the contractile and metabolic properties of the wrist extensor in 12 C-5/6 tetraplegic individuals. The wrist extensor muscles were stimulated for 30 min/day, 5 days/week, for 12 weeks, using either a high-resistance (Hr) or a low-resistance (Lr) protocol. Total work output was similar in both protocols. The nontrained arm was used as a control. Maximum voluntary torque increased in the Hr (P < 0.05) but not the Lr group. Electrically stimulated peak tetanic torque at 15 HZ, 30 HZ, and 50 HZ were unchanged in the Lr group and tended to increase only at 15 HZ (P < 0.1) in the Hr group. Resistance to fatigue, however, increased (P < 0.05) in both Hr (42%) and Lr (41%) groups. Muscle metabolism was evaluated by (31)P nuclear magnetic resonance spectroscopy ((31)P-NMRS) during and following a continuous 40-s 10-HZ contraction. In the Hr group the cost of contraction decreased by 38% (P < 0.05) and the half-time of phosphocreatine (PCr) recovery was shortened by 52% (P < 0.05). Thus, long-term electrically induced stimulation of the wrist extensor muscles in spinal cord injury (SCI) increases fatigue resistance independent of training pattern. However, only the Hr protocol increased muscle strength and was shown to improve muscle aerobic metabolism after training. Muscle Nerve 27: 72-80, 2003

Effects of electrical stimulation-induced leg training on skeletal muscle adaptability in spinal cord injury

Neuromuscular electrical stimulation has grown in popularity as a therapeutic device for training and an ambulation aid to human paralyzed muscle. Despite its current clinical use, few studies have attempted to concurrently investigate the functional and intramuscular adaptations which occur after electrical stimulation training. Six individuals with a spinal cord injury performed 10 weeks of electrical stimulation leg cycle training (30 min d(-1), 3 d week(-1)). The paralyzed vastus lateralis muscle showed significant alterations in skeletal muscle characteristics after the training, indicated by an improvement in total work output (52-112 kJ; P < 0.05), an increase in fiber cross-sectional area (18 to 41 x 10(2) microm(2); P < 0.05), a reduction in the percentage of type IIX fibers (75% to 12%; P < 0.05), a decrease in myosin heavy chain IIx (68% to 44%; P < 0.05), an increase in capillary density (2-3.5 capillaries around fiber; P < 0.05) and increases in activity levels of citrate synthase (7-16 mU mg(-1) protein) and hexokinase (1.2-2.4 mU mg(-1) protein). This study showed that 10 weeks of electrical stimulation training of human paralyzed muscle induces concurrent improvements in functional capacity and oxidative metabolism.

Onset of electrical stimulation leg cycling in individuals with paraplegia

PURPOSE

This study investigated cardiovascular and hemodynamic responses during the transition from rest to electrical stimulation-induced leg cycling exercise (ES-LCE) in individuals with chronic paraplegia (PARA).

METHODS

Ten PARA (T(4)-T(9); ASIA A) participated in this study. Heart rate (HR), mean arterial pressure (MAP), stroke volume (SV), and cardiac output (Q) were measured on a beat-to-beat basis at rest and during the first 60 s of ES-LCE.

RESULTS

PARA exhibited two discrete MAP responses during ES-LCE. Those with high thoracic lesions (HIGH: T(4) -T(6), = 5) responded to ES-LCE with a significant rise in MAP (maxdelta 8.3 +/- 3.6 mm Hg), whereas MAP did not exhibit any sustained change from resting values during ES-LCE in those subjects with lower lesions (LOW: T -T, = 5). In HIGH PARA, the immediate increase in MAP corresponded to a decrease in HR (maxdelta 6.8 +/- 3.1 b x min(-1)), which returned toward resting levels by the end of 60 s. In contrast, for LOW PARA there was no change in HR from resting levels during transition to ES-LCE. In both subgroups, SV and Q were not significantly increased during ES-LCE.

CONCLUSION

These results suggest that the on-transient responses of MAP during ES-LCE in HIGH PARA elicited reflex changes in HR via the arterial baroreflex, whereas in LOW PARA, an unchanged HR from rest was likely due to a constant MAP during ES-LCE.

Effect of muscle electrostimulation on afferent activities from tibialis anterior muscle after nerve repair by self-anastomosis

Numerous previous studies were devoted to the regeneration of motoneurons toward a denervated muscle after nerve repair by self-anastomosis but, to date, few investigations have evaluated the regeneration of sensory muscle endings. In a previous electrophysiological study (Decherchi et al., 2001) we showed that the functional characteristics of tibialis anterior muscle afferents are affected after self-anastomosis of the peroneal nerve even when the neuromuscular preparation was not chronically stimulated. The present study examines the regeneration of groups I-II (mechanosensitive) and groups III-IV (metabosensitive) muscle afferents by evaluating the recovery of their response to different test agents after self-anastomosis combined or not with chronic muscle stimulation for a 10-weeks period. We compared five groups of rats: C, control; L, nerve lesion without suture; LS, nerve lesion with suture; LSE(m): nerve lesion plus chronic muscle stimulation with a monophasic rectangular current; and LSE(b): nerve lesion plus chronic stimulation with a biphasic current with modulations of pulse duration and frequency, eliciting a pattern of activity resembling that delivered by the nerve to the muscle. Compared to the control group, (1) muscle kept only its original weight in the LSE(b) group, (2) in the LS group the response curve to tendon vibration was shifted toward the highest mechanical frequencies and the response of groups III-IV afferents after fatiguing muscle stimulation lowered, (3) in the LSE(m) group, the pattern of activation of mechanoreceptors by tendon vibrations was altered as in the LS group, and the response of metabosensitive afferents to KCl injections was markedly reduced, (4) in the LSE(b) group, the response to tendon vibration was not modified and the activation of metabosensitive units by increased extracellular potassium chloride concentration was conserved. Both LSE(b) and LSE(m) conditions were ineffective to maintain the post muscle stimulation activation of metabosensitive units as well as their activation by injected lactic acid solutions. Our data indicate that chronic muscle electrostimulation partially favors the recovery of mechano- and metabosensitivity in a denervated muscle and that biphasic modulated currents seem to provide better results.

Control of leg-powered paraplegic cycling using stimulation of the lumbo-sacral anterior spinal nerve roots

We investigated leg-powered cycling in a recumbent tricycle for a paraplegic using functional electrical stimulation (FES) with the lumbo-sacral anterior root stimulator implant (LARSI). A female complete T9 paraplegic had a stimulator for the anterior L2 to S2 spinal roots (bilaterally) implanted in 1994. She was provided with equipment for daily FES cycling exercise at home. The cycling controller applies a pattern of stimulation in each of 16 crank angle phases. A 7-bit shaft encoder measures the crank angle with adequate precision. Each pattern was originally chosen to give the greatest propulsive force in that position when there was no motion. However, dynamically, some reduction in co-contraction is needed; also the patterns are applied with a preset advance time. Maximal power is obtained with an advance of 250 ms, which compensates for muscle response delay and accommodates changes in cadence (from about 25 to 85 rpm). With this system, she has cycled 1.2 km at a time on gently undulating road. We found that spinal root stimulation gives sufficient control over the muscles in the legs to produce a fluid cycling gait. We propose that root stimulation for leg cycling exercise may be a practicable and valuable function for paraplegics following spinal cord injury.