Effects of exercise on muscle activation and metabolism in multiple sclerosis

Alteration of skeletal muscle energy metabolism assessed by 31 P MRS in clinical routine: Part 2. Clinical application

In this second part of a two-part paper, we intend to demonstrate the impact of the previously proposed advanced quality control pipeline. To understand its benefit and challenge the proposed methodology in a real scenario, we chose to compare the outcome when applying it to the analysis of two patient populations with significant but highly different types of fatigue: COVID-19 and multiple sclerosis (MS). 31 P-MRS was performed on a 3 T clinical MRI, in 19 COVID-19 patients, 38 MS patients, and 40 matched healthy controls. Dynamic acquisitions using an MR-compatible ergometer ran over a rest (40 s), exercise (2 min), and a recovery phase (6 min). Long and short TR acquisitions were also made at rest for T1 correction. The advanced data quality control pipeline presented in Part 1 is applied to the selected patient cohorts to investigate its impact on clinical outcomes. We first used power and sample size analysis to estimate objectively the impact of adding the quality control score (QCS). Then, comparisons between patients and healthy control groups using the validated QCS were performed using unpaired t tests or Mann-Whitney tests (p < 0.05). The application of the QCS resulted in increased statistical power, changed the values of several outcome measures, and reduced variability (standard deviation). A significant difference was found between the T1PCr and T1Pi values of MS patients and healthy controls. Furthermore, the use of a fixed correction factor led to systematically higher estimated concentrations of PCr and Pi than when using individually corrected factors. We observed significant differences between the two patient populations and healthy controls for resting [PCr]-MS only, [Pi ], [ADP], [H2 PO4 - ], and pH-COVID-19 only, and post-exercise [PCr], [Pi ], and [H2 PO4 - ]-MS only. The dynamic indicators τPCr , τPi , ViPCr , and Vmax were reduced for COVID-19 and MS patients compared with controls. Our results show that QCS in dynamic 31 P-MRS studies results in smaller data variability and therefore impacts study sample size and power. Although QCS resulted in discarded data and therefore reduced the acceptable data and subject numbers, this rigorous and unbiased approach allowed for proper assessment of muscle metabolites and metabolism in patient populations. The outcomes include an increased metabolite T1 , which directly affects the T1 correction factor applied to the amplitudes of the metabolite, and a prolonged τPCr , indicating reduced muscle oxidative capacity for patients with MS and COVID-19.

Voluntary muscle activation in people with multiple sclerosis is reduced across a wide range of forces following maximal effort-fatiguing contractions

Although multiple sclerosis (MS) is frequently associated with motor impairment, little is known about how muscle activation is affected with MS. The aim of this study was to use transcranial magnetic stimulation (TMS) and motor nerve stimulation to investigate voluntary muscle activation in people with MS across a range of contraction forces. Ten people with MS (39 ± 7 yr) and 10 healthy controls (40 ± 5 yr) performed elbow flexions at target contraction forces of 25%, 50%, 75%, 90%, and 100% maximal voluntary contraction (MVC) while electromyography (EMG) of the biceps brachii was recorded. Sustained elbow flexion MVCs were then performed until force declined to 60% of baseline MVC, where the target contraction forces were again examined but after the sustained MVC. Following the sustained MVC, there was a reduction in biceps EMG amplitude (P < 0.01) and motor cortical voluntary activation (P < 0.01) for the MS group across all contraction intensities. There was also an increase in the rate of torque development for motor nerve-resting twitches in the MS group following the sustained MVC (P = 0.03). Despite the MS group reporting higher fatigue severity scale scores (P < 0.01), disease duration was a better predictor of muscle activation for the MS group (r = -0.757, P = 0.01). These findings indicate that voluntary muscle activation is compromised in people with MS following maximal effort contractions, which may be associated with disease duration rather than self-reports of fatigue.NEW & NOTEWORTHY We use transcranial magnetic stimulation to demonstrate that people with relapsing-remitting multiple sclerosis (MS) have a reduced ability to activate muscles following maximal effort-fatiguing contractions. A reduced ability to activate the elbow flexor muscles after a fatiguing contraction was associated with disease duration and not self-reported levels of fatigue.

The rate of force relaxation scaling factor is highly sensitive to detect upper and lower extremity motor deficiencies in mildly affected people with multiple sclerosis

BACKGROUND

The motor symptoms affecting upper and lower extremity functioning in people with multiple sclerosis (PwMS) are considered the cardinal symptoms of multiple sclerosis. There is still a need for outcome measures that can sensitively evaluate these symptoms. We aimed to investigate the sensitivity of the isometric outcomes (maximum force; Fmax, maximum rate of force development; RFDmax, rate of force development scaling factor; RFD-SF, and rate of force relaxation scaling factor; RFR-SF) and standard clinical tests (9-hole peg test; 9HPT and timed 25-feet walk test; T25FW) in detecting the upper and lower extremity motor deficiencies in PwMS and also in a subgroup of mildly affected PwMS whose performance in standard clinical tests were similar to controls.

METHODS

Twenty-nine PwMS (age: 47.9 (8.6) years, relapsing-remitting type, expanded disability status scale: 2.5 (1.5)) and their age- and gender-matched controls completed an identical testing protocol in the upper (grip force muscles) and lower (knee extensors) extremities. For each extremity, we assessed Fmax, RFDmax, RFD-SF, and RFR-SF. Additionally, participants completed standard clinical tests for the evaluation of upper- (9HPT) and lower-extremity (T25FW) function. Comparisons were made between controls and PwMS 1) using all study participants and 2) including only mildly affected PwMS whose performance in standard functional tests was comparable to controls. Independent sample t-tests were utilized to compare groups, with a p-value set at 0.01 to correct for multiple comparisons. P-values and effect sizes were used to evaluate the sensitivity of the outcome measures in detecting group differences.

RESULTS

Our results indicate that most isometric outcomes and standard functional tests were sensitive in detecting motor deficiencies in both upper and lower extremities between groups (p<0.001). Among participants, 16 PwMS in 9HPT and 11 PwMS in T25FW demonstrated performance similar to that of the control group (9HPT: 18.85 (2.20) s vs 17.81 (2.19) s; p=0.19) and (T25FW: 3.60 (0.42) s vs 3.58 (0.29) s; p=0.92). The results of the comparisons between mildly affected PwMS and their controls indicate that RFR-SF is the only sensitive isometric outcome to detect differences between groups in the upper (-8.24 (0.76) 1/s vs -8.93 (0.6) 1/s; p=0.008) and lower extremity (-5.86 (1.13) 1/s vs -7.71 (1.11) 1/s; p<0.001).

CONCLUSION

The rate of force relaxation scaling factor, which assesses the ability to rapidly relax muscle forces after quick contractions, demonstrates high sensitivity in detecting motor deficiencies in PwMS, even when the current standard clinical outcomes fail to detect these differences. Our findings emphasize the importance of future randomized controlled trials focusing on rehabilitative and therapeutic interventions that specifically target muscle force relaxation to enhance motor functioning in PwMS.

Neural bases of motor fatigue in multiple sclerosis: A multimodal approach using neuromuscular assessment and TMS-EEG

Motor fatigue is one of the most common symptoms in multiple sclerosis (MS) patients. Previous studies suggested that increased motor fatigue in MS may arise at the central nervous system level. However, the mechanisms underlying central motor fatigue in MS are still unclear. This paper investigated whether central motor fatigue in MS reflects impaired corticospinal transmission or suboptimal primary motor cortex (M1) output (supraspinal fatigue). Furthermore, we sought to identify whether central motor fatigue is associated with abnormal M1 excitability and connectivity within the sensorimotor network. Twenty-two patients affected by relapsing-remitting MS and 15 healthy controls (HCs) performed repeated blocks of contraction at different percentages of maximal voluntary contraction with the right first dorsal interosseus muscle until exhaustion. Peripheral, central, and supraspinal components of motor fatigue were quantified by a neuromuscular assessment based on the superimposed twitch evoked by peripheral nerve and transcranial magnetic stimulation (TMS). Corticospinal transmission, excitability and inhibition during the task were tested by measurement of motor evoked potential (MEP) latency, amplitude, and cortical silent period (CSP). M1 excitability and connectivity was measured by TMS-evoked electroencephalography (EEG) potentials (TEPs) elicited by M1 stimulation before and after the task. Patients completed fewer blocks of contraction and showed higher values of central and supraspinal fatigue than HCs. We found no MEP or CSP differences between MS patients and HCs. Patients showed a post-fatigue increase in TEPs propagation from M1 to the rest of the cortex and in source-reconstructed activity within the sensorimotor network, in contrast to the reduction observed in HCs. Post-fatigue increase in source-reconstructed TEPs correlated with supraspinal fatigue values. To conclude, MS-related motor fatigue is caused by central mechanisms related explicitly to suboptimal M1 output rather than impaired corticospinal transmission. Furthermore, by adopting a TMS-EEG approach, we proved that suboptimal M1 output in MS patients is associated with abnormal task-related modulation of M1 connectivity within the sensorimotor network. Our findings shed new light on the central mechanisms of motor fatigue in MS by highlighting a possible role of abnormal sensorimotor network dynamics. These novel results may point to new therapeutical targets for fatigue in MS.

How is neuromuscular fatigability affected by perceived fatigue and disability in people with multiple sclerosis?

Whereas fatigue is recognized to be the main complaint of patients with multiple sclerosis (PwMS), its etiology, and particularly the role of resistance to fatigability and its interplay with disability level, remains unclear. The purposes of this review were to (i) clarify the relationship between fatigue/disability and neuromuscular performance in PwMS and (ii) review the corticospinal and muscular mechanisms of voluntary muscle contraction that are altered by multiple sclerosis, and how they may be influenced by disability level or fatigue. Neuromuscular function at rest and during exercise are more susceptible to impairement, due to deficits in voluntary activation, when the disability is greater. Fatigue level is related to resistance to fatigability but not to neuromuscular function at rest. Neurophysiological parameters related to signal transmission such as central motor conduction time, motor evoked potentials amplitude and latency are affected by disability and fatigue levels but their relative role in the impaired production of torque remain unclear. Nonetheless, cortical reorganization represents the most likely explanation for the heightened fatigability during exercise for highly fatigued and/or disabled PwMS. Further research is needed to decipher how the fatigue and disability could influence fatigability for an ecological task, especially at the corticospinal level.

Multiple Sclerosis and Mastication: An EMG Study

Purpose: Aim of the study is to determine the activity of masseter muscle formed by mastication of different foods in individuals with multiple sclerosis (MS). Material and Methods: 12 women with MS and 12 healthy women were included in the study. 3 grams of hazelnut and chewing gum were given to individuals 20 separate times. Activities of the left and the right masseter muscles during mastication were recorded by using surface electromyography (EMG) device. Results: Values obtained from healthy women were higher than those obtained from patients with MS for both foods and both sides. Conclusion: The changes in the central and peripheral nervous systems of the patients affect chewing function.

The pathophysiology of motor fatigue and fatigability in multiple sclerosis

Multiple Sclerosis (MS) is a heterogeneous immune mediated disease of the central nervous system (CNS). Fatigue is one of the most common and disabling symptom of MS. It interferes with daily activities on the level of cognition and motor endurance. Motor fatigue can either result from lesions in cortical networks or motor pathways (“primary fatigue”) or it may be a consequence of detraining with subsequent adaptions of muscle and autonomic function. Programmed exercise interventions are used frequently to increase physical fitness in MS-patients. Studies investigating the effects of training on aerobic capacity, objective endurance and perceived fatigability have yielded heterogenous results, most likely due to the heterogeneity of interventions and patients, but probably also due to the non-uniform pathophysiology of fatigability among MS-patients. The aim of this review is to summarize the current knowledge on the pathophysiology of motor fatigability with special reference to the basic exercise physiology that underlies our understanding of both pathogenesis and treatment interventions.

People with multiple sclerosis have reduced TMS-evoked motor cortical output compared with healthy individuals during fatiguing submaximal contractions

People with multiple sclerosis (PwMS) typically experience greater levels of exercise-induced fatigue compared with healthy individuals. Therefore, this study examined performance fatigability in PwMS when executing a prolonged submaximal contraction. Nine PwMS (38 ± 7 yr, 6 females) and nine healthy controls (35 ± 6 yr, 4 females) performed an elbow flexion at 15% maximal voluntary contraction (MVC) for 26 min. MVCs were performed every 2 min during, and following, the contraction to determine if maximal force was impaired by the low-intensity contraction. Single-pulse transcranial magnetic stimulation (TMS) was delivered to the primary motor cortex with a circular coil during each MVC and during the submaximal contraction. Superimposed and resting twitches were calculated from elbow flexion torque, whereas motor-evoked potentials were calculated from biceps brachii electromyography. Ratings of perceived exertion (RPE) were obtained before each MVC. During the fatiguing contraction protocol, the MS group exhibited a reduced MVC torque compared with the healthy control group (P = 0.044), which aligned with group differences in biceps brachii EMG activity (P = 0.022) and superimposed twitch amplitude (P = 0.016). Fatigue-related decrements in MVC torque (P = 0.044) and biceps brachii EMG activity (P = 0.043) demonstrated in the MS group persisted throughout recovery. However, MS did not affect the RPE during the fatigue task. These findings suggest that PwMS may have greater levels of performance fatigability due to decreased voluntary drive from the motor cortex, which is not associated with greater ratings of perceived exertion.NEW & NOTEWORTHY By combining TMS and motor nerve stimulation during a low-intensity exercise task, we were able to uncover the contribution that different levels of the CNS have during fatiguing exercise in PwMS. Our findings are novel and revealed that PwMS experienced decreased voluntary drive from the motor cortex during a low-intensity sustained fatiguing task that was associated with heightened levels of performance fatigability.

Effects of Combined Endurance and Resistance Training in Women With Multiple Sclerosis: A Randomized Controlled Study

Purpose: To test the hypothesis that combined resistance and endurance training would improve muscle strength, fatigue, depression, and quality of life in persons with MS.

Methods: Twenty-seven women with MS were randomly assigned to either control (CON, n = 13) or the experimental (EXP, n = 14) group. The participants in the EXP group trained twice a week for 12 weeks, followed by 12 weeks of detraining. Both CON and EXP groups were tested before and after 12 weeks of the intervention period, as well as 12 weeks after training cessation (follow-up), where measures of muscle strength, fatigue, depression, and quality of life were evaluated.

Results: There were significant changes in maximal voluntary isometric contraction (MVIC), 1RM leg extension, and 1RM chest press following the intervention period in the EXP group (P < 0.05), but not in the CON group (P > 0.05). These changes persisted after 12 weeks of detraining. Similar findings were found for fatigue, depression, and physical and mental composites of quality of life.

Conclusion: These results suggest that combined exercise training, at a minimum, prevents the disease-related deterioration of muscular performance and quality of life and well-being in persons with MS.

Neuroprotective role of galantamine with/without physical exercise in experimental autoimmune encephalomyelitis in rats

AIMS

The fact that physical activity besides central cholinergic enhancement contributes in improving neuronal function and spastic plasticity, recommends the use of the anticholinesterase and cholinergic drug galantamine with/without exercise in the management of the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis (MS).

MATERIALS AND METHODS

Sedentary and 14 days exercised male Sprague Dawley rats were subjected to EAE. Hereafter, exercised rats continued on rotarod for 30 min for 17 consecutive days. At the onset of symptoms (day 13), EAE sedentary/exercised groups were subdivided into untreated and post-treated with galantamine. The disease progression was assessed by EAE score, motor performance, and biochemically using cerebrospinal fluid (CSF). Cerebellum and brain stem samples were used for histopathology and immunohistochemistry analysis.

KEY FINDINGS

Galantamine decreased EAE score of sedentary/exercised rats and enhanced their motor performance. Galantamine with/without exercise inhibited CSF levels of tumor necrosis factor (TNF)-α, interleukin (IL)-6), and Bcl-2-associated X protein (Bax), besides caspase-3 and forkhead box P3 (Foxp3) expression in the brain stem. Contrariwise, it has elevated CSF levels of brain derived neurotrophic factor (BDNF) and B-cell lymphoma (Bcl-2) and enhanced remyelination of cerebral neurons. Noteworthy, exercise boosted the drug effect on Bcl-2 and Bax.

SIGNIFICANCE

The neuroprotective effect of galantamine against EAE was associated with anti-inflammatory and anti-apoptotic potentials, along with increasing BDNF and remyelination. It also normalized regulatory T-cells levels in the brain stem. The impact of the add-on of exercise was markedly manifested in reducing neuronal apoptosis.

Impaired central drive to plantarflexors and minimal ankle proprioceptive deficit in people with multiple sclerosis

BACKGROUND

A common and disruptive symptom of multiple sclerosis is difficulty in walking. Deficits in ankle proprioception and in plantarflexor muscle function may contribute to these mobility issues. In this study, ankle proprioceptive ability and plantarflexor performance of people with multiple sclerosis (PwMS) were compared to healthy controls to determine whether multiple sclerosis causes impairments in these systems.

METHODS

PwMS (n = 30, median EDSS 4.0, IQR 2) were compared to age- and sex-matched healthy controls (n = 30) across tests of ankle proprioception and plantarflexor muscle performance. Proprioceptive tests: detection of passive movement, reaction time and ankle joint position sense. Plantarflexor performance: strength, fatigue, recovery and voluntary activation (level of neural drive) of the plantarflexor muscles, assessed through brief and sustained fatiguing (2 min) isometric maximal voluntary contractions with nerve stimulation to evoke superimposed and resting muscle twitches.

RESULTS

PwMS had unimpaired movement detection and joint position sense but had a slower reaction time to respond with plantarflexion to an imposed ankle movement (between group difference = 0.11 [95% CI; 0.05 to 0.17] s). During brief, maximal contractions PwMS produced lower torque (difference = -25.1 [-42.0 to -8.2] Nm) with reduced voluntary activation (difference = -14.6 [-25.1 to -4.1]%) but no impairment of the muscle itself (resting twitch torque difference = 0.3 [-2.8 to 2.2] Nm). At the end of the fatiguing contraction, neural drive decreased for PwMS (-19.5 [-27.1 to -11.9]%, p <0.0001) but not for controls (-2.5 [-6.9 to 1.8]%, p = 0.242). Fatigue did not affect the resting twitch size for controls (-1.3 [-2.7 to -0.03] Nm, p = 0.134) or PwMS (-0.1 [-1.1 to 1.0] Nm, p = 0.90).

CONCLUSIONS

PwMS showed no deficit in their ability to sense ankle position or imposed movements but were slow when a motor response was required. Their plantarflexor muscles produced similar torque with electrical stimulation but voluntary strength was impaired.  Both groups experienced overall fatigue following the 2-minute maximal voluntary contraction but PwMS also had significantly reduced neural drive indicating central fatigue. PwMS showed mainly central deficits in motor output at the ankle with little impairment of proprioceptive acuity.

Creatine and multiple sclerosis

Multiple sclerosis (MS) is a complex and debilitating neurodegenerative disease, with unknown cause(s), unpredictable prognosis, and rather limited treatment options. MS is often accompanied by various metabolic disturbances, with impaired creatine metabolism may play a role in its pathogenesis and the clinical course of the disease. This review summarizes human trials describing alterations in creatine levels in the nervous system and other tissues during MS, affects how certain medications for MS affect brain creatine concentrations, and discusses a possible demand for exogenous creatine as an adjunct therapeutic agent in the management of MS. Creatine metabolism seems to be dysfunctional in MS, indicating a low metabolic state of the brain and other relevant organs in this unpredictable demyelinating disease. A disease-driven brain creatine deficit could be seen as a distinctive pathological facet of severe MS that might be approached with targeted therapies in aim to restore creatine homeostasis.

Shared Regulatory Pathways Reveal Novel Genetic Correlations Between Grip Strength and Neuromuscular Disorders

Muscle weakness is a common consequence of both aging (sarcopenia) and neuromuscular disorders (NMD). Whilst genome-wide association (GWA) studies have identified genetic variants associated with grip strength (GS; measure of muscle strength/weakness) and NMDs, including multiple sclerosis (MS), myasthenia gravis (MG) and amyotrophic lateral sclerosis (ALS), it is not known whether there are common mechanisms between these phenotypes. To examine this, we have integrated GS and NMD associated genetic variants (single nucleotide polymorphisms; SNPs) in a multimorbid analysis that leverages high-throughput chromatin interaction (Hi-C) data and expression quantitative trait loci data to identify target genes (i.e., SNP-mediated gene regulation). Biological pathways enriched by these genes were then identified using next-generation pathway enrichment analysis. Lastly, druggable genes were identified using drug gene interaction (DGI) database. We identified gene regulatory mechanisms associated with GS, MG, MS, and ALS. The SNPs associated with GS regulate a subset of genes that are also regulated by the SNPs of MS, MG, and ALS. Yet, we did not find any genes commonly regulated by all four phenotype associated SNPs. By contrast, we identified significant enrichment in three pathways (mTOR signaling, axon guidance, and alcoholism) that are commonly affected by the gene regulatory mechanisms associated with all four phenotypes. 13% of the genes we identified were known drug targets, and GS shares at least one druggable gene and pathway with each of the NMD phenotypes. We have identified significant biological overlaps between GS and NMD, demonstrating the potential for spatial genetic analysis to identify common mechanisms between potential multimorbid phenotypes. Collectively, our results form the foundation for a shift from a gene to a pathway-based approach to the rationale design of therapeutic interventions and treatments for NMD.

Body composition and disability in people with multiple sclerosis: A dual-energy x-ray absorptiometry study

INTRODUCTION

Body composition refers to the relative distribution of different tissue types within the body, including fat, lean, and bone tissues. There is evidence for associations between body composition and the development of multiple sclerosis (MS). The relationship between body composition and disease progression and disability accumulation, however, is unclear.

OBJECTIVES

To examine: a) differences in overall and regional body composition by disability status in persons with multiple sclerosis (MS); and b) the relationship between body composition and other outcomes reflecting impairments and limitations due to MS.

METHODS

Cross-sectional investigation of 47 ambulatory persons with relapsing remitting MS who were grouped by Expanded Disability Status Scale (EDSS) scores as having mild (1.0-4.0; n = 26) or moderate (4.5-6.5; n = 21) disability. Main outcome measures were whole-body and regional soft tissue composition (%body fat (BF), fat mass (FM), and fat-free soft tissue mass (FFM)), bone mineral content (BMC), and bone mineral density (BMD) determined from dual-energy X-ray absorptiometry (DXA). Other outcomes included physical fitness, mobility, cognitive processing speed, symptoms, and health-related quality of life (HRQOL).

RESULTS

Whole-body and regional %BF and FM were significantly higher, and whole-body and appendicular BMC and BMD were significantly lower in participants with moderate disability than those with mild disability (all p < .05). There were no significant differences in whole-body or regional FFM by disability status. In the overall sample, body fat correlated significantly with cardiorespiratory fitness (pr_s = -.52 to -.56), pain symptoms (pr_s = .32), and psychological HRQOL (pr_s = .34). FFM (pr_s = .38-.48) and BMC (pr_s = .53-.69) correlated primarily with measures of muscular strength.

CONCLUSIONS

Persons with MS who have greater disability present with higher body fat and lower bone tissue content and density than those with mild disability. These findings highlight the need for strategies that address potential changes in body composition with disability accumulation.

No association of leg strength asymmetry with walking ability, fatigability, and fatigue in multiple sclerosis

This cross-sectional study aims to determine whether leg strength asymmetries are associated with walking ability, objective measures of fatigability, or subjective perceptions of fatigue. Maximal knee extensor strength was assessed in 19 patients with multiple sclerosis (PwMS), and a symmetry index was calculated. Walking ability was determined through the total distance covered during a 6-min walk test (6MWT) and fatigability by calculating the change in distance covered between minutes 6 and 1. Perceptions of fatigue were assessed using the Fatigue Severity Scale and by obtaining ratings of perceived exertion during the first and final minute of the 6MWT. PwMS covered less distance (P=0.01) and perceived greater exertion (P<0.01) during minute 6 compared with minute 1. Knee extensor strength was asymmetric (P<0.01). The magnitude of asymmetry did not correlate with walking ability, fatigability, or measures of fatigue. Knee extensor strength asymmetry may not play an important role in prolonged walking performance in PwMS.

Modification of a three-compartment muscle fatigue model to predict peak torque decline during intermittent tasks

This study aimed to test whether adding a rest recovery parameter, r, to the analytical three-compartment controller (3CC) fatigue model (Xia and Frey Law, 2008) will improve fatigue estimates during intermittent contractions. The 3CC muscle fatigue model uses differential equations to predict the flow of muscle between three muscle states: Resting (MR), Active (MA), and Fatigued (MF). This model uses a feedback controller to match the active state to target loads and two joint-specific parameters: F, fatigue rate controlling flow from active to fatigued compartments) and R, the recovery rate controlling flow from the fatigued to the resting compartments. This model does well to predict intensity-endurance time curves for sustained isometric tasks. However, previous studies find when rest intervals are present that the model over predicts fatigue. Intermittent rest periods would allow for the occurrence of subsequent reactive vasodilation and post-contraction hyperemia. We hypothesize a modified 3CC-r fatigue model will improve predictions of force decay during intermittent contractions with the addition of a rest recovery parameter, r, to augment recovery during rest intervals, representing muscle re-perfusion. A meta-analysis compiling intermittent fatigue data from 63 publications reporting decline in peak torque (% torque decline) were used for comparison. The original model over-predicted fatigue development from 19 to 29% torque decline; the addition of a rest multiplier significantly improved fatigue estimates to 6-10% torque decline. We conclude the addition of a rest multiplier to the three-compartment controller fatigue model provides a physiologically consistent modification for tasks involving rest intervals, resulting in improved estimates of muscle fatigue.

Estimation of critical end-test torque using neuromuscular electrical stimulation of the quadriceps in humans

Characterization of critical power/torque (CP/CT) during voluntary exercise requires maximal effort, making difficult for those with neuromuscular impairments. To address this issue we sought to determine if electrically stimulated intermittent isometric exercise resulted in a critical end-test torque (ETT) that behaved similar to voluntary CT. In the first experiment participants (n = 9) completed four bouts of stimulated exercise at a 3:2 duty cycle, at frequencies of 100, 50, 25 Hz, and a low frequency below ETT (Sub-ETT; ≤ 15 Hz). The second experiment (n = 20) consisted of four bouts at a 2:2 duty cycle-two bouts at 100 Hz, one at an intermediate frequency (15-30 Hz), and one at Sub-ETT. The third experiment (n = 12) consisted of two bouts at 50 Hz at a 3:2 duty* cycle with proximal blood flow occlusion during one of the bouts. ETT torque was similar (p ≥ 0.43) within and among stimulation frequencies in experiment 1. No fatigue was observed during the Sub-ETT bouts (p > 0.05). For experiment 2, ETT was similar at 100 Hz and at the intermediate frequency (p ≥ 0.29). Again, Sub-ETT stimulation did not result in fatigue (p > 0.05). Altering oxygen delivery by altering the duty cycle (3:2 vs. 2:2; p = 0.02) and by occlusion (p < 0.001) resulted in lower ETT values. Stimulated exercise resulted in an ETT that was consistent from day-to-day and similar regardless of initial torque, as long as that torque exceeded ETT, and was sensitive to oxygen delivery. As such we propose it represents a parameter similar to voluntary CT.

Aberrant peak lactate response in MS

BACKGROUND

The peak blood lactate response to an exhaustive exercise test in a number of chronic conditions has been shown to differ from that seen in healthy, untrained individuals. However, this has not been investigated for patients with multiple sclerosis (MS).

OBJECTIVE

The main objective was to determine and compare the peak blood lactate response to exercise and the maximal workload between two groups of MS patients with different illness severity.

METHODS

Twenty-five patients with a relapsing-remitting disease course (Group RR) and 41 patients with a secondary- or primary chronic progressive disease course (group CP) performed an exhaustive incremental bicycle ergometry. Peak blood lactate, maximal workload, peak oxygen consumption and maximal heart rate were measured.

RESULTS

The peak blood lactate levels and maximal workload differed significantly between the groups (group CP < group RR; p < 0.001). Furthermore spiroergometric peak performance markers in both groups were significantly lower than predicted for healthy age and sex matched untrained groups.

CONCLUSION

A reduced peak blood lactate response to exercise is a novel finding for MS patients. This calls into doubt if the lactate performance tests and lactate thresholds used for healthy individuals can be transferred to MS patients.

In Vivo Assessment of Mitochondrial Dysfunction in Clinical Populations Using Near-Infrared Spectroscopy

The ability to sustain submaximal exercise is largely dependent on the oxidative capacity of mitochondria within skeletal muscle, and impairments in oxidative metabolism have been implicated in many neurologic and cardiovascular pathologies. Here we review studies which have demonstrated the utility of Near-infrared spectroscopy (NIRS) as a method of evaluating of skeletal muscle mitochondrial dysfunction in clinical human populations. NIRS has been previously used to noninvasively measure tissue oxygen saturation, but recent studies have demonstrated the utility of NIRS as a method of evaluating skeletal muscle oxidative capacity using post-exercise recovery kinetics of oxygen metabolism. In comparison to historical methods of measuring muscle metabolic dysfunction in vivo, NIRS provides a more versatile and economical method of evaluating mitochondrial oxidative capacity in humans. These advantages generate great potential for the clinical applicability of NIRS as a means of evaluating muscle dysfunction in clinical populations.

No Muscle Is an Island: Integrative Perspectives on Muscle Fatigue

Muscle fatigue has been studied with a variety approaches, tools and technologies. The foci of these studies have ranged tremendously, from molecules to the entire organism. Single cell and animal models have been used to gain mechanistic insight into the fatigue process. The theme of this review is the concept that the mechanisms of muscle fatigue do not occur in isolation in vivo: muscular work is supported by many complex physiological systems, any of which could fail during exercise and thus contribute to fatigue. To advance our overall understanding of fatigue, a combination of models and approaches is necessary. In this review, we examine the roles that neuromuscular properties, intracellular glycogen, oxygen metabolism, and blood flow play in the fatigue process during exercise and pathological conditions.

Central and peripheral fatigue development in the shoulder muscle with obesity during an isometric endurance task

BACKGROUND

Fatigue increases the likelihood of developing work-related musculoskeletal disorders and injury. Due to the physiological and neuromuscular changes that accompany obesity, it may alter the fatigue development mechanism and exacerbate injury risk. The upper extremities have the highest incidence rates for work-related musculoskeletal disorders. Therefore, the goals of this study were to investigate the effect of obesity on central vs. peripheral fatigue as well as on the physical signs of fatigue on the middle deltoid muscle.

METHODS

A measure of central activation ratio was used to quantify central fatigue by considering the increment in the torque output by superimposed twitch relative to its corresponding maximum voluntary contraction. For this purpose, electrical stimulation was delivered at the middle deltoid muscles of 22 non-obese (18 < body mass index (BMI) < 25 kg/m2) and 17 obese (30 < BMI < 40 kg/m2) individuals aged 18-32 years old. Participants completed superimposed maximum voluntary isometric contractions of shoulder abduction before and after a sustained isometric fatiguing task at either 30 or 60% of the muscle capacity. Differences in endurance time, torque fluctuation, torque loss, and muscle activity measured by an electromyography sensor were also investigated.

RESULTS

A greater reduction of voluntary activation of motor units (p = 0.001) with fatigue was observed for individuals who are obese. Contrary to the effect of obesity on central fatigue, a trend toward reduced peripheral fatigue (p = 0.06) was observed for the obese group compared to the non-obese group. On average, a 14% higher rate of torque loss per second was observed among individuals with obesity in comparison to non-obese participants.

CONCLUSIONS

The observed greater contribution of central fatigue during the sustained endurance tasks suggests that among young healthy obese individuals, the faster fatigue development with obesity, commonly reported in the literature, is most likely due to the central elements rather than the peripheral factors. This finding has implications for fatigue prevention programs during sustained exertions and can help to develop training, work, and rest schedules considering obesity.

Neuromuscular fatigue during exercise: Methodological considerations, etiology and potential role in chronic fatigue

The term fatigue is used to describe a distressing and persistent symptom of physical and/or mental tiredness in certain clinical populations, with distinct but ultimately complex, multifactorial and heterogenous pathophysiology. Chronic fatigue impacts on quality of life, reduces the capacity to perform activities of daily living, and is typically measured using subjective self-report tools. Fatigue also refers to an acute reduction in the ability to produce maximal force or power due to exercise. The classical measurement of exercise-induced fatigue involves neuromuscular assessments before and after a fatiguing task. The limitations and alternatives to this approach are reviewed in this paper in relation to the lower limb and whole-body exercise, given the functional relevance to locomotion, rehabilitation and activities of daily living. It is suggested that under some circumstances, alterations in the central and/or peripheral mechanisms of fatigue during exercise may be related to the sensations of chronic fatigue. As such, the neurophysiological correlates of exercise-induced fatigue are briefly examined in two clinical examples where chronic fatigue is common: cancer survivors and people with multiple sclerosis. This review highlights the relationship between objective measures of fatigability with whole-body exercise and perceptions of fatigue as a priority for future research, given the importance of exercise in relieving symptoms of chronic fatigue and/or overall disease management. As chronic fatigue is likely to be specific to the individual and unlikely to be due to a simple biological or psychosocial explanation, tailored exercise programmes are a potential target for therapeutic intervention.

Potential pathophysiological pathways that can explain the positive effects of exercise on fatigue in multiple sclerosis: A scoping review

BACKGROUND

Fatigue is one of the most common and most disabling symptoms of multiple sclerosis (MS). It is a multidimensional and complex symptom with multifaceted origins, involving both central and peripheral fatigue mechanisms. Exercise has proven to be safe for people with MS, with cumulating evidence supporting significant reductions in fatigue. However, the potential pathophysiological pathways that can explain the positive effects of exercise on fatigue in MS remain elusive.

OBJECTIVES

The objectives were, in PwMS (1) to update the knowledge on the pathophysiology underlying primary and secondary fatigue, and (2) to discuss potential pathophysiological pathways that can explain the positive effects of exercise on MS fatigue.

METHODS

A comprehensive literature search of six databases (PubMed, Embase, Cochrane Library, PEDro, CINAHL and SPORTDiscus) was performed. To be included, the study had to 1) enroll participants with definite MS according to defined criteria, 2) assess explicit pathophysiological mechanisms related to MS fatigue, 3) be available in English, Danish or French, and 4) had undergone peer-review.

RESULTS

A total of 234 studies fulfilled the inclusion criteria. Primary MS fatigue mainly originated from a dysfunction of central nervous system neuronal circuits secondary to increased inflammation, reduced glucose metabolism, brain atrophy and diffuse demyelination and axonal lesions. Secondary MS fatigue was linked with sleep disturbances, depression, cognitive impairments, and deconditioning. Cardiovascular, immunologic, neuroendocrine, and neurotrophic changes associated with exercise may alleviate primary MS fatigue while exercise may improve secondary MS fatigue through symptomatic improvement of deconditioning, sleep disorders, and depression.

CONCLUSIONS

>30 primary and secondary pathophysiological fatigue pathways were identified underlining the multidimensionality and complexity of MS fatigue. Though the underlying key cellular and molecular cascades still have to be fully elucidated, exercise holds the potential to alleviate MS fatigue, through both primary and secondary fatigue pathways.

Exercise as medicine - evidence for prescribing exercise as therapy in 26 different chronic diseases

This review provides the reader with the up-to-date evidence-based basis for prescribing exercise as medicine in the treatment of 26 different diseases: psychiatric diseases (depression, anxiety, stress, schizophrenia); neurological diseases (dementia, Parkinson's disease, multiple sclerosis); metabolic diseases (obesity, hyperlipidemia, metabolic syndrome, polycystic ovarian syndrome, type 2 diabetes, type 1 diabetes); cardiovascular diseases (hypertension, coronary heart disease, heart failure, cerebral apoplexy, and claudication intermittent); pulmonary diseases (chronic obstructive pulmonary disease, asthma, cystic fibrosis); musculo-skeletal disorders (osteoarthritis, osteoporosis, back pain, rheumatoid arthritis); and cancer. The effect of exercise therapy on disease pathogenesis and symptoms are given and the possible mechanisms of action are discussed. We have interpreted the scientific literature and for each disease, we provide the reader with our best advice regarding the optimal type and dose for prescription of exercise.

Fatigue in Multiple Sclerosis: Misconceptions and Future Research Directions

Fatigue is one of the most disabling side effects in people with multiple sclerosis. While this fact is well known, there has been a remarkable lack of progress in determining the pathophysiological mechanisms behind fatigue and the establishment of effective treatments. The main barrier has been the lack of a unified definition of fatigue that can be objectively tested with validated experimental models. In this “perspective article” we propose the use of the following model and definition of fatigue: the decrease in physical and/or mental performance that results from changes in central, psychological, and/or peripheral factors. These changes depend on the task being performed, the environmental conditions it is performed in, and the physical and mental capacity of the individual. Our definition and model of fatigue outlines specific causes of fatigue and how it affects task performance. We also outline the strengths and weaknesses of commonly used measures of fatigue and suggest, based on our model and definition, new research strategies, which should include multiple measures. These studies should be mechanistic with validated experimental models to determine changes in central, psychological, and/or peripheral factors that explain fatigue. The proposed new research strategies may lead to the identification of the origins of MS related fatigue and the development of new, more effective treatments.

Factors limiting maximal oxygen uptake in exertional monoparesis

Strength and maximal oxygen uptake (VO2max) for each leg were compared in a trained multiple sclerosis (MS) patient with exertional left monoparesis. Left quadriceps strength and left leg VO2max were 22% and 30% lower, respectively, compared to the right (control) leg. Because the same O2 delivery system served each leg during exercise, VO2max of the paretic leg was not limited by cardiorespiratory factors but rather by strength and/or muscle oxidative capacity. However, training with monoparesis likely enhanced O2 extraction and aerobic work capacity of the right leg.

Evidence for a central mechanism in the process of fatigue in people with multiple sclerosis

The study aimed to establish quantitative and qualitative aspects of fatigue among a group of people with multiple sclerosis (MS) who had identified fatigue as a troublesome symptom and a control group of healthy adults. An interview, a fatigue diary and a fatigue-inducing experiment were designed and the Nottingham Health Profile was employed. People with MS experienced significantly more fatigue than healthy adults, on a daily basis. Factors noted to cause and to relieve fatigue were similar in people with MS and healthy adults. The only differences were that a hot bath improved fatigue in healthy adults and accentuated it in people with MS and that more of the healthy adults mentioned lack of sleep as a cause of fatigue. Physiological muscular fatigue during a quadriceps test was of similar magnitude in the two studied groups but the perceived fatigue levels were disproportionally high in the patient group. The results support the view that central mechanisms are responsible both for muscle weakness and for the sense of fatigue experienced so frequently in multiple sclerosis. This central mechanism is likely to reside in motor pathways within the nervous system. Further studies, measuring corticomotor conduction times, motor unit firing frequencies and metabolic factors, are recommended.

Impact of high intensity exercise on muscle morphology in EAE rats

The impact of high-intensity exercise on disease progression and muscle contractile properties in experimental autoimmune encephalomyelitis (EAE) remains unclear. Control (CON) and EAE rats were divided into sedentary and exercise groups. Before onset (experiment 1, n=40) and after hindquarter paralysis (experiment 2, n=40), isokinetic foot extensor strength, cross sectional area (CSA) of tibialis anterior (TA), extensor digitorum longus (EDL) and soleus (SOL) and brain-derived neurotrophic factor (BDNF) levels were assessed. EAE reduced muscle fiber CSA of TA, EDL and SOL. In general, exercise was not able to affect CSA, whereas it delayed hindquarter paralysis peak. CON muscle work peaked and declined, while it remained stable in EAE. BDNF-responses were not affected by EAE or exercise. In conclusion, EAE affected CSA-properties of TA, EDL and SOL, which could, partly, explain the absence of peak work during isokinetic muscle performance in EAE-animals. However, exercise was not able to prevent muscle fiber atrophy.

Skeletal muscle fatigue

Skeletal muscle fatigue is defined as the fall of force or power in response to contractile activity. Both the mechanisms of fatigue and the modes used to elicit it vary tremendously. Conceptual and technological advances allow the examination of fatigue from the level of the single molecule to the intact organism. Evaluation of muscle fatigue in a wide range of disease states builds on our understanding of basic function by revealing the sources of dysfunction in response to disease.

Exercise in multiple sclerosis

Exercise is an intervention that may be used in the management of multiple sclerosis (MS). Certain exercise physiology characteristics are commonly seen among persons with MS, particularly in the more debilitated. Studies have shown that properly prescribed exercise programs can improve modifiable impairments in MS. Exercise is generally safe and well tolerated. General guidelines are available for exercise prescription for the MS population. There are several recommendations that may help improve the quality of future MS exercise trials.

Resistance training and vibration improve muscle strength and functional capacity in female patients with multiple sclerosis

PURPOSE

The purpose of this study was to evaluate the effect of an eight-week progressive resistance training and vibration program on strength and ambulatory function in multiple sclerosis (MS) patients.

METHODS

Twenty-Four female MS patients with the following demographics: age 27-45 years, and expanded disability status scale (EDSS) 2-4, participated in this study. The subjects were randomly allocated to one of two groups. The exercise group (n = 12) trained according to a progressive program, mainly consisting of resistance training and vibration, three times a week for eight weeks and compared with subjects in the control group (n = 12) that received no intervention. Subjects completed one set of 5-12 reps at%50-70 maximal voluntary contraction (MVC). After 5-10 minutes rest, six postures on plate vibration were done. Isotonic MVC of knee extensors, abduction of the scapula and downward rotation of the scapular girdle muscle groups were predicted by using the Brzycki formula. Right leg balance (RLB), left leg balance (LLB), and walking speed (10-Meter Walk Test) were assessed before and after the training program. Descriptive statistics and Co-variance were used for analyzing data.

RESULTS

After eight weeks of training the exercise group showed significant increase in MVC of Knee extensors (32.3%), Abduction of the scapula (24.7%) and Downward Rotation Scapular (39.1%) muscle groups, RLB (33.5%), LLB (9.5%), and decrease in 10-Meter Walk Test (10MWT) (9.3%), (P<0.05).

CONCLUSIONS

The results of this study indicated this type of training can cause improvements in muscle strength and functional capacity in patients with multiple sclerosis.

Muscular and gait abnormalities in persons with early onset multiple sclerosis

BACKGROUND AND PURPOSE

Muscular and gait abnormalities are common complaints among persons with multiple sclerosis, even in the early stages of the disease. Our aim was to evaluate peak isometric strength, major lower limb muscle fatigue, and spatiotemporal gait parameters in persons with a first neurological event suggestive of multiple sclerosis, defined as a clinically isolated syndrome (CIS).

METHODS

Fifty-two individuals (36 women, 16 men) with CIS, aged 35.2 (SD = 7.2) with an Expanded Disability Status Scale score of 1.7 (SD = 1.3), participated in the study. Peak isometric torque and fatigue index were measured at the knee and ankle bilaterally as well spatiotemporal parameters of gait. Twenty-eight age- and gender-matched healthy subjects served as controls.

RESULTS

The CIS group demonstrated increased muscle fatigue, and greater ankle muscle torque asymmetries compared with the control group. The overall fatigue index scores intensified on an average of 40% in the CIS group (27% vs 19% in controls). Participants in the CIS group walked with a larger step length difference, longer step time difference, wider base of support, and prolonged double support period compared with the control group. Positive correlations were identified between double support period and some muscle parameters.

DISCUSSION AND CONCLUSION

At this early stage of clinically isolated syndrome, evidence of a reduction in lower limb motor performance can already be identified. The possibility of early identification and potential for developing an intervention program that may alter treatment outcome warrants further exploration.

Corticospinal output during muscular fatigue differs in multiple sclerosis patients compared to healthy controls

Background:

In multiple sclerosis (MS), fatigue is a common and often disabling symptom. It has multiple causes with central motor fatigue playing an important role.

Objective:

The objective of this study was to analyse the central motor conduction changes in relation to muscle contraction force during muscle fatigue and recovery in MS patients compared to healthy controls.

Methods:

A total of 23 MS patients with fatigue and 13 healthy subjects were assessed during 2 minutes of fatiguing exercise of the abductor digiti minimi muscle of the hand and the subsequent 7 minutes of recovery. Central motor conduction was quantified by transcranial magnetic stimulation using the triple stimulation protocol and calculating a central conduction index (CCI).

Results:

Force declined to 36% of the pre-exercise level (SD 16%; p < 0.01) in MS patients and to 44% (SD 9%, p < 0.01) in healthy subjects (group differences, not statistically significant). The decline of the CCI was significantly less marked in patients (–20%, SD 26%, p < 0.05) than in healthy subjects (–57%, SD 15%, p < 0.05; group differences, p < 0.05). The decline of force and CCI were not correlated in either group.

Conclusions:

During a fatiguing exercise, the decline in central motor conduction is significantly less pronounced in MS patients than healthy subjects, although the reduction of force is similar.

Management options in multiple sclerosis-associated fatigue

INTRODUCTION

Multiple sclerosis (MS) is a chronic, inflammatory, autoimmune disease of the CNS. Its characteristic early clinical course includes exacerbations and remissions of neurologic disability. Fatigue is one of the most common symptoms of MS and is associated with a reduced quality of life; it is described as the worst symptom of the disease by 50 - 60% of patients. Yet, due to limitations of available evidence, current therapeutic approaches for treating fatigue are based mainly on preliminary studies and expert consensus.

AREAS COVERED

This review summarizes current knowledge on the physiopathology, diagnosis and therapeutic options for MS-associated fatigue, including both pharmacological and non-pharmacological strategies.

EXPERT OPINION

Large, rigorously designed trials can provide more reliable results on the efficacy of interventions for fatigue, their functional impact on everyday activities and patient quality of life. Future research should also address a better understanding of the physiopathologic mechanisms of fatigue and the development and validation of objective assessment tools to be used together with patient self-ratings.

Effects of long-term resistance training and simultaneous electro-stimulation on muscle strength and functional mobility in multiple sclerosis

Background: Resistance training studies in multiple sclerosis (MS) often use short intervention periods. Furthermore, training efficiency could be optimized by unilateral training and/or electrical stimulation.

Objective: To examine the effect(s) of unilateral long-term (20 weeks) standardized resistance training with and without simultaneous electro-stimulation on leg muscle strength and overall functional mobility.

Methods: A randomized controlled trial involving 36 persons with MS. At baseline (PRE) and after 10 (MID) and 20 (POST) weeks of standardized (ACSM) light to moderately intense unilateral leg resistance training (RESO, n = 11) only or resistance training with simultaneous electro-stimulation (RESE, n = 11, 100 Hz, biphasic symmetrical wave, 400 µs), maximal isometric strength of the knee extensors and flexors (45°, 90° knee angle) and dynamic (60–180°/s) knee-extensor strength was measured and compared with a control group (CON, n = 14). Functional mobility was evaluated using the Timed Get Up and Go, Timed 25 Foot Walk, Two-Minute Walk Test, Functional Reach and Rivermead Mobility Index.

Results: Maximal isometric knee extensor (90°, MID: +10 ± 3%, POST: +10 ± 4%) in RESO and knee flexor (45°, POST: +7 ± 4%; 90°, POST: +9 ± 5%) in RESE strength increased ( p < 0.05) compared with CON but RESO and RESE did not differ. Also, impaired legs responded positively to resistance training (unilateral leg strength analysis) and functional reaching increased significantly in RESO (+18%) compared with CON. Dynamic muscle strength and the remaining functional mobility tests did not change.

Conclusion: Long-term light to moderately intense resistance training improves muscle strength in persons with MS but simultaneous electro-stimulation does not further improve training outcome.

Endurance exercise improves walking distance in MS patients with fatigue

OBJECTIVES

Effects of endurance training in multiple sclerosis (MS) patients complaining of motor fatigue.

MATERIALS AND METHODS

Thirty MS patients complaining of fatigue with low to moderate disabilities randomly allocated to the intervention (thrice weekly 45-min intervals of endurance exercise) or control treatment (three 45-min episodes of stretching, balance training and coordination), both as 'add-on' therapy for 3 weeks during inpatient rehabilitation.

RESULTS

Maximal walking distance before intervention averaged 1043 +/- 568 and 1163 +/- 750 m in the two groups. The intervention group increased its maximal walking distance by 650 +/- 474 m. The control group extended its walking distance by 96 +/- 70 m.

CONCLUSIONS

The present data confirm a strong effect of endurance exercise on maximal walking distance. Remarkably, there were no parallel improvements on the Modified Fatigue Impact Scale, the Beck Depression Inventory and the Hamburg Quality of Life Questionnaire for MS.

Fatigued patients with multiple sclerosis have impaired central muscle activation

BACKGROUND

The pathogenesis of fatigue in multiple sclerosis (MS) is poorly understood.

OBJECTIVE

To elucidate the role of central motor activation we hypothesized that patients with primary fatigue have impaired central motor function and increased fatigability as compared to secondary fatigued and non-fatigued patients.

METHODS

Sixty patients with relapsing remitting MS and an Expanded Disability Status Scale score <or= 3.5 were recruited and grouped as fatigued (Fatigue Severity Scale (FSS) >or= 5.0) or non-fatigued (FSS <or= 4.0). Nineteen patients were primary fatigued, 20 secondary fatigued and 21 non-fatigued. Maximal voluntary contraction, central activation and peripheral activation were determined by percutaneous twitch interpolation of the right quadriceps muscle.

RESULTS

Maximal voluntary contraction was similar between groups but did relate to scores of fatigue. Peripheral activation was similar in all groups. Central activation was impaired in both groups of fatigued patients compared to non-fatigued patients being 0.96(0.05) in primary fatigued and 0.96(0.04) in secondary fatigued versus 0.99(0.1) in non-fatigued patients. The impairment of central motor activation was related to degree of fatigue in all patients. During fatiguing exercise there was a similar loss of strength, without any time differences between the three groups.

CONCLUSION

We conclude that impaired central motor activation is involved in MS-fatigue.

Leg power asymmetry and postural control in women with multiple sclerosis

The extent of and the interactions between muscle strength, walking speed, postural control, and symptomatic fatigue in multiple sclerosis (MS) are not known, nor are the effects of bilateral strength asymmetries on these variables.

PURPOSE

To quantify the magnitude of and the associations between bilateral strength and limb-loading asymmetries, postural control, and symptomatic fatigue in women with MS.

METHODS

Peak knee extensor (KE) and dorsiflexor (DF) isometric torque and isotonic power were assessed bilaterally in 12 women with MS (Expanded Disability Status Scale = 4 +/- 1) and 12 age-matched female controls using a Biodex dynamometer (Biodex Medical, Shirley, NY). Center of pressure (CoP) variability during 20 s of quiet stance was measured in the anteroposterior (AP) and the mediolateral (ML) directions using adjacent force plates. Bilateral asymmetry scores were calculated for power and torque. Normal and brisk walk times (25 ft) and symptomatic fatigue (Visual Analog Fatigue Scale and Fatigue Severity Scale) were measured before strength and balance testing.

RESULTS

Fatigue was greater and walk times (normal and brisk) were longer in MS (P < or = 0.01). Dorsiflexor (DF) isometric torque and power and knee extensor (KE) isometric strength were similar between groups. KE power was lower (mean +/- SD = 21.5 +/- 16.2%; P < or = 0.05) and KE power asymmetry was greater in MS than in controls (9.2 +/- 6.9%; P = 0.02). Postural variability of the CoP was greater in the AP direction in MS than in controls (7.52 +/- 3.02 and 4.33 +/- 1.79 mm, respectively; P = 0.005). KE power asymmetry was associated with fatigue and walk times (P < or = 0.02), and AP CoP variability was correlated with fatigue, walk times, and power asymmetries (P < or = 0.05).

CONCLUSIONS

These data provide new evidence of a potential role for KE strength asymmetries in the symptomatic fatigue and physical dysfunction of persons with MS, possibly through an effect on postural stability.

Multiple sclerosis and physical exercise: recommendations for the application of resistance-, endurance- and combined training

This review summarizes the existing knowledge regarding the effects of physical exercise in patients suffering from multiple sclerosis (MS). Furthermore, recommendations are given regarding exercise prescription for MS patients and for future study directions. Previously, MS patients were advised not to participate in physical exercise. During recent years, it has been increasingly acknowledged that exercise benefits MS patients. The requirement for exercise in MS patients is emphasized by their physiological profile, which probably reflects both the effects of the disease per se and the reversible effects of an inactive lifestyle. To date the effects of exercise have only been studied in moderately impaired MS patients with an EDSS score of less than 7. Evidence exists for recommending participation in endurance training at low to moderate intensity, as the existing literature demonstrates that MS patients can both tolerate and benefit from this training modality. Also, resistance training of moderate intensity seems to be well tolerated and to have beneficial effects on MS patients, but the methodological quality of the existing evidence is in general low and the number of studies is limited. Only two studies have evaluated the effects of combined resistance- and endurance training, making solid conclusions regarding this training modality impossible.

Origin of fatigue in multiple sclerosis: review of the literature

Fatigue is one of the most common and most disabling symptoms of multiple sclerosis (MS). Although numerous studies have tried to reveal it, no definite pathogenesis factor behind this fatigue has been identified. Fatigue may be directly related to the disease mechanisms (primary fatigue) or may be secondary to non-disease-specific factors. Primary fatigue may be the result of inflammation, demyelination, or axonal loss. A suggested functional cortical reorganization may result in a higher energy demand in certain brain areas, culminating in an increase of fatigue perception. Higher levels of some immune markers were found in patients with MS-related fatigue, whereas other studies rejected this hypothesis. There may be a disturbance in the neuroendocrine system related to fatigue, but it is not clear whether this is either the result of the interaction with immune activation or the trigger of this process. Fatigue may be secondary to sleep problems, which are frequently present in MS and in their turn result from urinary problems, spasms, pain, or anxiety. Pharmacologic treatment of MS (symptoms) may also provoke fatigue. The evidence for reduced activity as a cause of secondary fatigue in MS is inconsistent. Psychological functioning may at least play a role in the persistence of fatigue. Research did not reach consensus about the association of fatigue with clinical or demographic variables, such as age, gender, disability, type of MS, education level, and disease duration. In conclusion, it is more likely to explain fatigue from a multifactor perspective than to ascribe it to one mechanism. The current evidence on the pathogenesis of primary and secondary fatigue in MS is limited by inconsistency in defining specific aspects of the concept fatigue, by the lack of appropriate assessment tools, and by the use of heterogeneous samples. Future research should overcome these limitations and also include longitudinal designs.

Physiological Basis of Fatigue

This work summarizes our knowledge of the physiological basis of fatigue and the effects of exercise and pharmacological interventions on fatigue. Fatigue may be defined as physical and/or mental weariness resulting from exertion, that is, an inability to continue exercise at the same intensity with a resultant deterioration in performance. The concept of deconditioning in patients is discussed as well as the implications for their rehabilitation and exercise. Because fatigue may result from a number of causes, including loss of muscle mass, deconditioning, nutritional deficiencies, oxygen delivery, and anemia, it should be treated comprehensively. Antifatigue therapy should be the standard of care for most chronic conditions associated with fatigue.

Fatigue in progressive multiple sclerosis is associated with low levels of dehydroepiandrosterone

BACKGROUND AND OBJECTIVE

Fatigue is one of the most limiting symptoms in multiple sclerosis (MS) and the mechanisms underlying its origin are poorly understood. Our aim was to test whether fatigue in MS is associated with endocrine markers.

METHODS

We longitudinally studied 73 progressive MS patients. Fatigue was assessed at baseline and at 3, 6, 12 and 24 months using the Fatigue Severity Scale (FSS). Given the longitudinal design of our study, patients were labelled as sustained fatigued when FSS scores were >5.0 at all time points, and as non-fatigued when FSS scores were < or = 5.0 at all time points. Serum levels of dehydroepiandrosterone (DHEA), its sulphated conjugate (DHEAS) and cortisol were measured at each time point.

RESULTS

Twenty-nine patients scored >5.0 in the FSS at all time points, and 9 patients (12.3%) scored 5.0 at all time points. Mean baseline levels of DHEAS and DHEA were lower in MS patients with sustained fatigue when compared to patients without fatigue (P = 0.01 and P = 0.03 respectively). Analysis of DHEAS and DHEA over time showed significantly lower hormone levels in patients with fatigue [F(1,31) = 6.14, P=0.019 for DHEAS; F(1,32) = 6.63, P=0.015 for DHEA].

CONCLUSIONS

Fatigue in progressive MS could be related to low serum levels of DHEA and DHEAS. Our results suggest that these hormones should be considered as biological markers of fatigue in MS patients and that hormone replacement may thus be tested as an option to treat fatigue in MS patients.

Comparison of the influence of different rehabilitation programmes on clinical, spirometric and spiroergometric parameters in patients with multiple sclerosis

PURPOSE

The aim of this study was to compare the effect of four different programmes on spiroergometric, spirometric and clinical parameters in multiple sclerosis (MS) patients.

METHODS

One hundred and twelve MS patients were divided into four groups. The first group underwent neurophysiologically based physiotherapy, the second aerobic training, the third combined therapy (neurophysiologically based physiotherapy and aerobic training) and the fourth did not change any habits. Seventeen patients did not finish the study. Patients were examined on impairment (Expanded Disability Status Scale), disability (Barthel Index), handicap (Environment Status Scale), quality of life (Multiple Sclerosis Quality of Life), fatigue (Modified Fatigue Impact Scale), depression (Beck Depression Inventory Score), respiratory function (spirometric parameters on spirometry) and physical fitness (spiroergometric parameters on a bicycle ergometer).

RESULTS

The patients who participated in one of our training programmes showed a significant improvement of the examined parameters in comparison to those who did not change their present habits. Each of the four training programmes had a different impact on the parameters, which means that each of them had a different effect. The neurophysiologically based physiotherapy had the greatest impact on impairment, and the aerobic training on spirometric and spiroergometric parameters. All methods (the neurophysiologically based physiotherapy, the aerobic training and the combined programme) had an impact on fatigue.