Effects of exercise on muscle activation and metabolism in multiple sclerosis

[Pathophysiology and treatment of fatigue in multiple sclerosis]

Patients suffering from multiple sclerosis (MS) frequently complain of fatigue (53 to 92 percent depending on studies). Fatigue can be one of the most disabling symptoms of MS and presents as physical or mental fatigue in daily living activities. Besides this permanent feeling of exhaustion, MS patients can suffer from an abnormal tiredness and lack of energy after a given motor or mental task, which defines fatigability. A number of studies explored the origins of fatigue and fatigability by means of subjective and objective tools. The implication of central nervous system dysfunctions has been established in several studies; however the contribution of peripheral nervous system factors and systemic abnormalities associated with inflammatory and immunological parameters was also suggested. The aim of this review is to present the different types of fatigue and fatigability occurring in MS patients, their origins, the investigation tools which allow the quantification of fatigue and fatigability and characterization of their mechanisms. The currently available therapeutic strategies that have been proposed to relieve this disabling symptom are presented.

Fatigue and multiple sclerosis

Even if the definition and pathophysiology of fatigue in multiple sclerosis (MS) are still debated, and despite the scarcity of objective markers correlated with the subjective sensation of fatigue, a review of the literature shows the importance of its detection and management, and allows one to propose therapeutic strategies. Fatigue is not only the most frequently reported symptom in MS, but also a frequent source of activity and participation limitations, psychological distress, and impairment of quality of life. Its management, which must be initiated early, is based on a comprehensive evaluation of its characteristics and consequences (sometimes with the use of scales such as the Fatigue Severity Scale and the Modified Fatigue Impact Scale), and on the identification of many potential contributing factors (psychological disorders, sleep disturbances, pain, infections and other comorbidities, medications, and deconditioning). Rehabilitative interventions are essential to the treatment of fatigue. Beyond the traditional energy conservation strategies and cooling techniques, several randomized controlled studies have demonstrated the positive impact of aerobic exercise. Medications are partially beneficial, and with the exception of amantadine, their efficacy has not been confirmed by randomized double-blind trials.

Symptom Change With Exercise Is a Temporary Phenomenon for People With Multiple Sclerosis

OBJECTIVE

To determine the impact of a single exercise session on function, fatigue, and sensory symptoms for people with multiple sclerosis (MS).

DESIGN

This pilot study was designed as a before-after trial. Demographic and response-to-exercise measures were taken before exercise, repeated immediately after exercise, and followed up again 24 hours later.

SETTING

Three metropolitan centers of an MS society.

PARTICIPANTS

A prospective sample of 34 subjects with MS who were referred for physiotherapy for an exercise program and who could attend an MS society center.

INTERVENTIONS

Subjects performed an individually prescribed exercise session, which was at a commencement level and included strengthening, stretches, and fitness exercises. Subjects exercised for between 5 to 45 minutes (mean, 17.4 min) at an intensity of 7 to 17 (median, 12) on the Borg rating of perceived exertion (RPE) scale.

MAIN OUTCOME MEASURES

All outcome measures were self-rated by subjects and included the Borg RPE scale, a questionnaire for sensory symptom description, and visual analog scales for rating of fatigue, function, and intensity of sensory symptoms.

RESULTS

Subjective levels of fatigue and function immediately postexercise and 24 hours postexercise did not differ significantly from pre-exercise levels. However, over 40% of subjects experienced a temporary increase in number of sensory symptoms, 44% experienced an increase in the intensity of sensory symptoms, and 29% experienced an increase in both number and intensity immediately postexercise.

CONCLUSIONS

This small study found that when people with MS undertake exercise at a commencement level, they can expect that sensory symptoms may change temporarily, but they are unlikely to have any deleterious changes in fatigue and function.

Fatigue and therapeutic exercise

Fatigue is a common symptom in patients with neurologic disease. Mechanisms of fatigue are still incompletely understood. In this paper, we review recent studies of fatigue in common neurologic conditions and discuss therapeutic interventions. In particular, the role of therapeutic exercise is examined in both health and disease.

Neural and metabolic mechanisms of excessive muscle fatigue in maintenance hemodialysis patients

Dialysis patients have severe exercise limitations related to metabolic disturbances, but muscle fatigue has not been well studied in this population. We investigated the magnitude and mechanisms of fatigue of the ankle dorsiflexor muscles in patients on maintenance hemodialysis. Thirty-three dialysis patients and twelve healthy control subjects performed incremental isometric dorsiflexion exercise, beginning at 10% of their maximal voluntary contraction (MVC) and increasing by 10% every 2 min. Muscle fatigue (fall of MVC), completeness of voluntary activation, and metabolic responses to exercise were measured. Before exercise, dialysis subjects exhibited reduced strength and impaired peripheral activation (lower compound muscle activation potential amplitude) but no metabolic perturbation. During exercise, dialysis subjects demonstrated threefold greater fatigue than controls with evidence of central activation failure but no change in peripheral activation. All metabolic parameters were significantly more perturbed at end exercise in dialysis subjects than in controls, including lower phosphocreatine (PCr) and pH, and higher Pi, Pi/PCr, and H2PO4−. Oxidative potential was markedly lower in patients than in controls [62.5 (SD 27.2) vs. 134.6 (SD 31.7), P < 0.0001]. Muscle fatigue was negatively correlated with oxidative potential among dialysis subjects ( r = −0.52, P = 0.04) but not controls. Changes in central activation ratio were also correlated with muscle fatigue in the dialysis subjects ( r = 0.59, P = 0.001) but not the controls. This study provides new information regarding the excessive muscular fatigue of dialysis patients and demonstrates that the mechanisms of this fatigue include both intramuscular energy metabolism and central activation failure.

Spiroergometric and spirometric parameters in patients with multiple sclerosis: are there any links between these parameters and fatigue, depression, neurological impairment, disability, handicap and quality of life in multiple sclerosis?

One-hundred and twelve patients with multiple sclerosis were selected as population-based sample and examined on impairment (Expanded Disability Status Scale), disability (Barthel Index), handicap (Environment Status Scale), the 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). The aim of the study was to examine and analyse (descriptive statistics) spiroergometric and spirometric parameters in patients with multiple sclerosis. Firstly, we tested the hypothesis whether spiroergometric and spirometric parameters are decreased and whether there are any correlations between these parameters and measures of impairment, depression, disability, handicap and quality of life. Secondly, we tested the hypothesis whether there is any correlation between a possible deconditioning and fatigue, and between a possible respiratory dysfunction and fatigue in multiple sclerosis. It results from this study that many spiroergometric parameters in patients with multiple sclerosis are significantly lowered in comparison to the population norm. A link can be found between some spiroergometric parameters and neurological impairment, disability, handicap and quality of life. It is not possible to prove any correlation between spiroergometric parameters and depression. From the spirometric parameters, these are expiratory flows that are significantly lowered in MS patients. It is not possible to prove any correlation between spirometric parameters and fatigue, depression, neurological impairment, duration of the disease, disability, handicap and quality of life in multiple sclerosis.

Exercise and Rehabilitation for Individuals with Multiple Sclerosis

It is the coexistence of physical and cognitive impairments, together with emotional and social issues in a disease with an uncertain course, that makes MS rehabilitation unique and challenging. Inpatient rehabilitation improves functional independence but has only limited success improving the level of neurologic impairment. Benefits are usually not long lasting. Severely disabled people derive equal or more benefit than those who are less disabled, but cognitive problems and ataxia tend to be refractory. There is now good evidence that exercise can improve fitness and function for those with mild MS and helps to maintain function for those with moderate to severe disability. Therapy can be performed over 6 to 15 weeks in outpatient or home-based settings or as a weekly day program lasting several months. Several different forms of exercise have been investigated. For most individuals, aerobic exercise that incorporates a degree of balance training and socialization is recommended. Time constraints, access, impairment level, personal preferences, motivations, and funding sources influence the prescription for exercise and other components of rehabilitation. Just as immunomodulatory drugs must be taken on a continual basis and be adjusted as the disease progresses, so should rehabilitation be viewed as an ongoing process to maintain and restore maximum function and QOL.

Cardiorespiratory response to walk in multiple sclerosis patients

To ascertain whether fatigue perception is linked to exertion dyspnea and/or to an impaired cardiorespiratory response during walk, 11 patients (8 females, age range 21-46 years) with multiple sclerosis (MS) and mild disability underwent the 6-min walk test. Ten healthy subjects (7 females, age range 25-49 years) were studied, as a control group. Patients did not differ from controls in spirometry, lung volumes and respiratory muscle strength. There was a significant difference in walk distance between patients and controls (P<0.001), but not in dyspnea perception. In patients, the walk distance significantly related to disability score (P<0.01), but not to fatigue. Compared to controls, patients had a significant decrease in oxygen pulse during walk (P<0.05) and a significant increase in the ventilatory equivalent of CO2 both at baseline and during walk (P<0.05). The relative contribution of both the tidal volume and of the ratio of inspiratory to total breathing cycle duration to the increase in minute ventilation during walk was significantly less in patients, as compared to controls (P<0.05). We conclude that in MS patients with mild disability, fatigue and exertion dyspnea are different sensations without any link and a peripheral limitation during walk can occur.

Functional relationships of central and peripheral muscle alterations in multiple sclerosis

The functional implications of central motor impairment and peripheral muscle alterations in multiple sclerosis are unclear. Muscle strength, central and peripheral activation, and symptomatic fatigue were investigated in 16 patients with multiple sclerosis (MS) and 18 control subjects. Voluntary and electrically stimulated isometric contractions were obtained from the ankle dorsiflexor muscles. Maximal voluntary contraction (MVC) was 27% lower in MS patients than controls, although electrically stimulated force was similar. Muscle fat-free cross-sectional area (CSA) was similar in both groups. These data indicate central activation impairment in MS. Such impairment in MS was further demonstrated by decreased foot-tap speed, rate of voluntary force development, and central activation ratio. Peripheral activation changes in MS patients were modest. Although stimulated tetanic force was similar, force relaxation was slower in MS patients compared to controls, resulting in a left-shifted force-frequency relationship in MS. Motor function changes were not associated with fatigue but were associated with impaired ambulation. Thus, weakness and walking impairment, but not fatigue, were related to impaired central activation in MS. These findings may help optimize rehabilitation strategies designed to improve function in persons with MS.

Exercise and Multiple Sclerosis

The pathophysiology of multiple sclerosis (MS) is characterised by fatigue, motor weakness, spasticity, poor balance, heat sensitivity and mental depression. Also, MS symptoms may lead to physical inactivity associated with the development of secondary diseases. Persons with MS are thus challenged by their disability when attempting to pursue an active lifestyle compatible with health-related fitness. Although exercise prescription is gaining favour as a therapeutic strategy to minimise the loss of functional capacity in chronic diseases, it remains under-utilised as an intervention strategy in the MS population. However, a growing number of studies indicate that exercise in patients with mild-to-moderate MS provides similar fitness and psychological benefits as it does in healthy controls. We reviewed numerous studies describing the responses of selected MS patients to acute and chronic exercise compared with healthy controls. All training studies reported positive outcomes that outweighed potential adverse effects of the exercise intervention. Based on our review, this article highlights the role of exercise prescription in the multidisciplinary approach to MS disease management for improving and maintaining functional capacity. Despite the often unpredictable clinical course of MS, exercise programmes designed to increase cardiorespiratory fitness, muscle strength and mobility provide benefits that enhance lifestyle activity and quality of life while reducing risk of secondary disorders. Recommendations for the evaluation of cardiorespiratory fitness, muscle performance and flexibility are presented as well as basic guidelines for individualised exercise testing and training in MS. Special considerations for exercise, including medical management concerns, programme modifications and supervision, in the MS population are discussed.

Fatigue associated with multiple sclerosis: diagnosis, impact and management

In patients with multiple sclerosis (MS) fatigue is the most common symptom and one of the most disabling features. As many as 40% have described it as the single most disabling symptom--a higher percentage than weakness, spasticity, motor problems, or bowel or bladder problems. The etiology and pathophysiology of MS-related fatigue remain unknown. Studies have failed to demonstrate an association between MS-related fatigue and the level of disability, clinical disease subtype, or gender, although recent data show an association between MS-related fatigue and depression and quality of life. Imaging studies using positron emission tomography suggest that fatigue in MS is related to hypometabolism of specific brain areas, including the frontal and subcortical circuits. The impact of fatigue on patient functioning and quality of life clearly warrants intervention. In addition to nonpharmacologic measures, such as exercise and energy conservation strategies, several pharmacologic agents have been evaluated for their ability to reduce MS-related fatigue, including amantadine, central nervous system stimulants (pemoline), and the novel wake-promoting agent modafinil.

Cross-bridge mechanisms of muscle weakness in multiple sclerosis

Vastus lateralis muscle biopsies were obtained from six individuals with multiple sclerosis (MS) having an Expanded Disability Status Score of 4.75 +/- 0.28, and from six age- and gender-matched individuals without MS. Biopsies from the MS group showed fewer fibers (31 +/- 4 vs. 46 +/- 4%) containing the type IIa myosin heavy chain (MHC) isoform exclusively. However, the percentage of fibers coexpressing type IIa and IIx MHC increased in direct proportion with MS disability status. The average unloaded shortening velocity of skinned fibers containing type I or IIa MHC did not differ between subject groups. Peak Ca(2+)-activated force was 11-13% lower in fibers from the MS group due to atrophy (type I and IIa fibers) and reduced specific force (type I fibers). Increasing intracellular inorganic phosphate (0-30 mM) or hydrogen ion (pH 7.0-6.2) reduced Ca(2+)-activated force in a manner that was independent of MS status. Thus, fibers from the MS group showed a subtle shift in fast MHC isoform coexpression and a modest reduction in cross-bridge number, density, or average force, with no change in maximal cross-bridge cycling rate or susceptibility to intracellular metabolites. These changes explain part of the muscle weakness and fatigue experienced by individuals with MS.

Body composition in ambulatory women with multiple sclerosis

OBJECTIVE

To compare whole-body fat mass and fat-free mass (FFM) in ambulatory patients with multiple sclerosis (MS) and control subjects without MS.

DESIGN

Nonrandomized controlled trial or cross-sectional study.

SETTING

An exercise physiology laboratory at a medical school.

PARTICIPANTS

Seventeen ambulatory patients with MS and 12 control subjects (all subjects were women). The median Expanded Disability Status Scale (EDSS) score was 4.0 for the individuals with MS.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Whole-body percentage of fat-free mass (%FFM), percentage of body fat (%BF), FFM, and fat mass.

RESULTS

A significant difference in age was observed between the groups; thus, age was used as a covariate in the body composition analyses. No significant differences were observed between the groups in %BF: 32.5+/-13.9 and 27.8+/-5.6 (P=.54) for MS and controls, respectively, or %FFM, 67.1+/-14.9 and 71.3+/-12.4 (P=.42) for MS and controls, respectively. For individuals with MS, no significant relation was observed between EDSS score and %BF (P=.24) or between EDSS score and %FFM (P=.24).

CONCLUSION

No significant differences were observed in body composition between ambulatory MS patients and controls. Furthermore, the EDSS score was not a significant predictor of %BF or %FFM for people with MS.

Human skeletal muscle responses vary with age and gender during fatigue due to incremental isometric exercise

The purpose of this study was to compare the magnitude and mechanisms of ankle dorsiflexor muscle fatigue in 20 young (33 +/- 6 yr, mean +/- SD) and 21 older (75 +/- 6 yr) healthy men and women of similar physical activity status. Noninvasive measures of central and peripheral (neuromuscular junction, sarcolemma) muscle activation, muscle contractile function, and intramuscular energy metabolism were made before, during, and after incremental isometric exercise. Older subjects fatigued less than young (P < 0.01); there was no effect of gender on fatigue (P = 0.24). For all subjects combined, fatigue was modestly related to preexercise strength (r = 0.49, P < 0.01). Neither central (central activation ratio) nor peripheral (compound muscle action potential) activation played a significant role in fatigue in any group. During exercise, intracellular concentrations of P(i) and H(2)PO increased more and pH fell more in young compared with older subjects (P < 0.01) and in men compared with women (P < 0.01). These varied metabolic responses to exercise suggest a greater reliance on nonoxidative sources of ATP in young compared with older subjects and in men compared with women. These results suggest that the mechanisms of fatigue vary with age and gender, regardless of whether differences in the magnitude of fatigue are observed.

Increased post-exercise facilitation of motor evoked potentials in multiple sclerosis

OBJECTIVES

To study post-exercise facilitation following a non-fatigue exercise in a homogenous group of multiple sclerosis (MS) patients with complaints of muscle fatigue.

METHODS

In 15 MS patients and matched controls motor evoked potentials (MEP) were recorded from the biceps brachii muscle at time delays of 0.5-30s after an isometric contraction with a torque of 50% of maximal voluntary contraction (MVC) maintained for 2-6s. In addition, MEP was recorded after isometric torque of 25, 50, and 100% of MVC maintained for 6s.

RESULTS

Isometric non-fatigue contraction induced significant post-exercise increase in MEP amplitude in MS patients compared with controls being most pronounced after a contraction for 6s. The post-exercise increase in MEP lasted for longer than 30s in MS patients.

CONCLUSIONS

Post-exercise increase of MEP amplitude following a non-fatigue exercise was significant in MS patients with complaints of muscle fatigue compared with healthy subjects.

Spinal and supraspinal factors in human muscle fatigue

Muscle fatigue is an exercise-induced reduction in maximal voluntary muscle force. It may arise not only because of peripheral changes at the level of the muscle, but also because the central nervous system fails to drive the motoneurons adequately. Evidence for "central" fatigue and the neural mechanisms underlying it are reviewed, together with its terminology and the methods used to reveal it. Much data suggest that voluntary activation of human motoneurons and muscle fibers is suboptimal and thus maximal voluntary force is commonly less than true maximal force. Hence, maximal voluntary strength can often be below true maximal muscle force. The technique of twitch interpolation has helped to reveal the changes in drive to motoneurons during fatigue. Voluntary activation usually diminishes during maximal voluntary isometric tasks, that is central fatigue develops, and motor unit firing rates decline. Transcranial magnetic stimulation over the motor cortex during fatiguing exercise has revealed focal changes in cortical excitability and inhibitability based on electromyographic (EMG) recordings, and a decline in supraspinal "drive" based on force recordings. Some of the changes in motor cortical behavior can be dissociated from the development of this "supraspinal" fatigue. Central changes also occur at a spinal level due to the altered input from muscle spindle, tendon organ, and group III and IV muscle afferents innervating the fatiguing muscle. Some intrinsic adaptive properties of the motoneurons help to minimize fatigue. A number of other central changes occur during fatigue and affect, for example, proprioception, tremor, and postural control. Human muscle fatigue does not simply reside in the muscle.

Muscle strength and fatigue during isokinetic exercise in individuals with multiple sclerosis

PURPOSE

To compare muscle strength and muscle fatigue of the knee extensors and flexors in individuals with multiple sclerosis (MS) and non-MS control subjects and to evaluate the reliability of muscle strength and muscle fatigue testing in these individuals.

METHODS

Thirty individuals (13 women and 2 men for both MS and control groups), age (mean +/- SD) 38.8 +/- 10 for MS and 33.1 +/- 7.6 yr for controls, participated in this investigation. Peak torque was measured on two occasions separated by approximately 7 d at 30, 60, 90, 120, 180 degrees.s(-1) with 2 min of recovery between each bout. The nondominant leg was tested followed by the dominant leg after 10 min of recovery. Subjects then performed three bouts of 30 flexions and extensions of the dominant leg at 180 degrees.s(-1) with 1 min of recovery between bouts.

RESULTS

The reliability of muscle torque was very high for individuals with MS (only 1 of 20 measurements with an ICC below 0.900). Total work was also highly reliable for MS, but the Fatigue Index (work during the last 15 contractions/work during the first 15 contractions) x 100 was not. Peak torque adjusted for age, body mass, and fat free mass (measured by whole body plethysmography; the Bod Pod; Life Measurement Instruments; Concord, CA) was significantly greater for controls than for MS for three of four lower body muscle groups tested. For the muscle fatigue test (3 bouts of 30 knee extensions and flexions at 180 degrees.s(-1)), the Fatigue Index was greater (less fatigue) for the knee extensors for controls than MS for the third bout. For flexion, the Fatigue Index was greater for controls than MS over the three bouts (group effect). Total work was significantly greater for controls than MS for the flexors (group effect) and approached significance for the extensors.

CONCLUSIONS

Individuals with MS were weaker than controls when data were adjusted for age, body mass, and fat free mass. This latter finding (force relative to age and fat free mass) suggests that there is a reduced ability to activate muscle mass in MS and/or the muscle mass of individuals with MS is of lower quality (i.e., reduced force/unit muscle mass) than controls.

Contractile properties and fatigue of quadriceps muscles in multiple sclerosis

Functional characteristics of electrically stimulated quadriceps muscles of patients with multiple sclerosis (MS) were determined to investigate whether adaptations in muscle properties contribute to the higher fatigability of these patients. The estimated maximal isometric force generating capacity of MS patients was only 11.2% (P < 0.05) lower than control subjects. However, the patients were only able to voluntarily exert 75 +/- 22% (n = 12) of their maximal capacity, against 94 +/- 6% (n = 7) for the control subjects. There were no differences in muscle speed, suggesting that muscle fiber distribution was not different in the MS patients due to reduced muscle usage. During a series of repeated contractions, greater decrements occurred in isometric force and in maximal rate of force rise in the MS patients (by 31.3 +/- 10.3% and 50.1 +/- 10.0%, respectively; n = 13) than control subjects (23.8 +/- 6.6% and 39.0 +/- 8.1%, n = 15), suggesting a lower oxidative capacity. The results indicate that increasing the mass of their muscles by training may help to reduce the excessive muscle fatigue of MS patients.

Age-related changes in muscle fatigue resistance in humans

OBJECTIVE

The goal of this study was to compare the relative contributions from the muscle and the central nervous system to muscle fatigue resistance in aging.

METHODS

Each subject carried out 90 s of sustained maximal voluntary isometric contraction (MVC) of the thumb using the thenar and forearm thumb muscles. Contractile capacity of the thenar muscles was assessed through tetanic stimulation of the median nerve. Interpolated doublets delivered during an MVC represented the overall voluntary activation level while transcranial cortical stimulation with an electromagnetic stimulator was used to assess motor output upstream from the corticomotoneuronal pathway.

RESULTS

Nine elderly subjects [four females and five males, 70+/-9 years old (mean+/-SD)] and 10 younger subjects (five females and five males, 30+/-6 years old) were tested. After the fatiguing exercise, the elderly group's MVC declined by 29% as opposed to 47% in the younger group (p<0.01). The elderly group's greater fatigue resistance was accounted for by increased fatigue resistance at the muscle level as well as in the central nervous system. At least some of the decline in the central motor drive was upstream from the corticomotoneuronal pathway.

CONCLUSION

The higher muscle fatigue resistance in the elderly group was attributable to differences in both the peripheral and central nervous systems.

Central fatigue during isometric exercise in amyotrophic lateral sclerosis

While both upper and lower motor neuron dysfunction may contribute to impaired muscle function in amyotrophic lateral sclerosis (ALS), the precise mechanisms of muscle fatigue have not been clarified in this disease. Therefore, the central and peripheral factors in muscle fatigue were investigated during intermittent submaximal isometric ankle dorsiflexion in 7 patients with ALS and 6 healthy control subjects. Voluntary and electrically stimulated force, central and peripheral indices of muscle activation, and intramuscular energy metabolism were measured before and during exercise. At the end of exercise, only the ALS group had an increase in the "added force" in response to a stimulus train imposed during maximal voluntary contraction, indicating significant central fatigue in ALS. In support of this conclusion, patients with ALS had less intramuscular phosphocreatine depletion and less fatigue of stimulated tetanic force during exercise compared to control. Thus, due to the central failure, there was decreased muscle activation resulting in a smaller metabolic demand and less fatigue within the muscle itself. These data demonstrate a major contribution of central factors to muscle fatigue in ALS.

Respiratory muscle weakness and respiratory muscle training in severely disabled multiple sclerosis patients

OBJECTIVE

To evaluate the contribution of respiratory muscle weakness (part 1) and respiratory muscle training (part 2) to pulmonary function, cough efficacy, and functional status in patients with advanced multiple sclerosis (MS).

DESIGN

Survey (part 1) and randomized controlled trial (part 2).

SETTING

Rehabilitation center for MS.

PATIENTS

Twenty-eight bedridden or wheelchair-bound MS patients (part 1); 18 patients were randomly assigned to a training group (n = 9) or a control group (n = 9) (part 2).

INTERVENTION

The training group (part 2) performed three series of 15 contractions against an expiratory resistance (60% maximum expiratory pressure [PEmax]) two times a day, whereas the control group performed breathing exercises to enhance maximal inspirations.

MAIN OUTCOME MEASURES

Forced vital capacity (FVC), inspiratory, and expiratory muscle strength (PImax and PEmax), neck flexion force (NFF), cough efficacy by means of the Pulmonary Index (PI), and functional status by means of the Extended Disability Status Scale (EDSS).

RESULTS

Part 1 revealed a significantly reduced FVC (43% +/- 26% predicted), PEmax (18% +/- 8% predicted), and PImax (27% +/- 11% predicted), whereas NFF was only mildly reduced (93% +/- 26% predicted). The PI (median score, 10) and EDSS (median score, 8.5) were severely reduced. PEmax was significantly correlated to FVC, EDSS, and PI (r = .77, -.79, and -.47, respectively). In stepwise multiple regression analysis. PEmax was the only factor contributing to the explained variance in FVC (R2 = .60), whereas body weight (R2 = .41) was the only factor for the PI. In part 2, changes in PImax and PEmax tended to be higher in the training group (p = .06 and p = .07, respectively). The PI was significantly improved after 3 months of training compared with the control group (p < .05). After 6 months, the PI remained significantly better in the training group.

CONCLUSIONS

Expiratory muscle strength was significantly reduced and related to FVC, cough efficacy, and functional status. Expiratory muscle training tended to enhance inspiratory and expiratory muscle strength. In addition, subjectively and objectively rated cough efficacy improved significantly and lasted for 3 months after training cessation.

Modalities of fatigue in multiple sclerosis: correlation with clinical and biological factors

Although different factors are probably involved in the etiology of fatigue in multiple sclerosis patients, no definite mechanism has been proposed. We have proposed that fatigue is a complex symptom that includes three clinical different entities (asthenia, fatigability and worsening of symptoms with effort). The goal of this study is to demonstrate if there is a peculiar mechanism for each of the different varieties of fatigue. A control sample of 155 patients (105 women, 50 men) with clinically definite MS was studied. Fatigue was measured using the Fatigue Descriptive Scale (FDS) and the Fatigue Severity Scale (FSS). Treatment, depression, anxiety, sleep and cellular immune status were studied too. Fatigue was a symptom in 118 patients (76.13%); 26 patients (22.03%) described it as asthenia (fatigue at rest); 85 patients (72.03%) as fatigability (fatigue with exercise), and seven patients (5.9%) as worsening of symptoms. The severity of pyramidal involvement was significantly more severe in patients suffering from fatigue; some immunological parameters were associated with fatigue as well. The discriminant analysis of the data shows that some of the immunoactivation parameters are associated with asthenia (F=21.5, P<0.001), and pyramidal tract involvement is associated with fatigability (F=10.5, P<0.001). Sleep disorders, anxiety and depression were linked with fatigue in a few patients. No relationship with treatment was proven. In conclusion, fatigue in MS seems to be a heterogeneous entity. Asthenia and fatigability may be different clinical entities. Certain immunoactivation parameters correlate with the presence of asthenia while pyramidal involvement is associated with fatigability.

Blunted pressor and intramuscular metabolic responses to voluntary isometric exercise in multiple sclerosis

To test the hypothesis that a lower mean arterial pressure (MAP) response during voluntary isometric exercise in multiple sclerosis (MS) is related to a dampened muscle metabolic signal, 9 MS and 11 control subjects performed an isometric dorsiflexor contraction at 30% maximal voluntary contraction until target failure (endurance time). We made continuous and noninvasive measurements of heart rate and MAP (Finapres) and of intramuscular pH and P(i) (phosphorus magnetic resonance spectroscopy) in a subset of 6 MS and 10 control subjects. Endurance times and change in heart rate were similar in MS and control subjects. The decrease in pH and increase in P(i) were less throughout exercise in MS compared with control subjects, as was the change in MAP response. Differences in muscle strength accounted for some of the difference in MAP response between groups. Cardiovascular responses during Valsalva and cold pressor tests were similar in MS and control subjects, suggesting that the blunted MAP response during exercise in MS was not due to a generalized dysautonomia. The dampened metabolic response in MS subjects was not explained by inadequate central muscle activation. These data suggest that the blunted pressor response to exercise in MS subjects may be largely appropriate to a blunted muscle metabolic response and differences in contracting muscle mass.

Sensory-motor and genito-sphincter dysfunctions in multiple sclerosis

Multiple sclerosis is a chronic demyeliniting disease of the central nervous system which is characterized by an extreme multiplicity of clinical features. Multiple sclerosis can have a profound impact on the quality of life of patients. The induced handicap varies from one patient to an other, and depends on the location of the demyeliniting lesions. Among the symptoms, sensory-motor disorders and genito-sphincter dysfunctions are some of the more disabling. Thus, up to 70% of patients suffer from urinary troubles, and 15 years after the onset of the illness, 50% of patients have difficulties for deambulation. A good knowledge of these pathologies is necessary to improve the management of patients suffering from multiple sclerosis.

Specific strength and voluntary muscle activation in young and elderly women and men

The extents to which decreased muscle size or activation are responsible for the decrease in strength commonly observed with aging remain unclear. Our purpose was to compare muscle isometric strength [maximum voluntary contraction (MVC)], cross-sectional area (CSA), specific strength (MVC/CSA), and voluntary activation in the ankle dorsiflexor muscles of 24 young (32 +/- 1 yr) and 24 elderly (72 +/- 1 yr) healthy men and women of similar physical activity level. Three measures of voluntary muscle activation were used: the central activation ratio [MVC/(MVC + superimposed force)], the maximal rate of voluntary isometric force development, and foot tap speed. Men had higher MVC and CSA than did women. Young men had higher MVC compared with elderly men [262 +/- 19 (SE) vs. 197 +/- 22 N, respectively], whereas MVC was similar in young and elderly women (136 +/- 15 vs. 149 +/- 16 N, respectively). CSA was greater in young compared with elderly subjects. There was no age-related impairment of specific strength, central activation ratio, or the rate of voluntary force development. Foot tap speed was reduced in elderly (34 +/- 1 taps/10 s) compared with young subjects (47 +/- 1 taps/10 s). These results suggest that isometric specific strength and the ability to fully and rapidly activate the dorsiflexor muscles during a single isometric contraction were unimpaired by aging. However, there was an age-related deficit in the ability to perform rapid repetitive dynamic contractions.

Correlation between symptom fatigue and muscular fatigue in multiple sclerosis

The symptom of fatigue is a frequent complaint in multiple sclerosis (MS) patients. Signs of fatigability have been documented in these patients as well. However, correlation with signs of objective fatigue had not been clarified in MS. The aim of this study was to ascertain the existence of muscular fatigue in multiple sclerosis patients, and to find out if there is a correlation between the subjective symptom of fatigue and muscular fatigue. Fifty MS patients and 50 age and sex matched volunteers were studied using isometric and isotonic tests using the dominant hand. Strength was studied in the baseline condition and also after recovery of either an isotonic (experiment A) or isometric effort (experiment B). Maximum strength, strength in relationship to weight, slope of fatigability in 11 consecutive contractions, and strength and duration of a maximum effort were calculated. Fatigue as a symptom was measured using the Fatigue Severity Scale (FSS) and the Fatigue Descriptive Scale (FDS). Non-parametric techniques were used for the statistical analysis. Patients with MS had less isometric and isotonic strength, but the recovery was the same as recovery in the control group. There was a negative linear correlation between the symptom of fatigue and the baseline strength. In conclusion, this study supports the existence of signs of muscular fatigue in MS patients. However, the recovery after exercise is normal. The correlation between the baseline scores in strength and the symptom of fatigue suggest that the same cause (probably pyramidal deficits) may be involved in both of them. Copyright 1998 Lippincott Williams & Wilkins

Functional significance of upper and lower motor neuron impairment in amyotrophic lateral sclerosis

The objective of this study was to examine the contribution of lower motor neuron (LMN) and upper motor neuron (UMN) dysfunction to weakness and impaired motor control in 27 patients with amyotrophic lateral sclerosis (ALS). Isometric strength was measured by dorsiflexor maximum voluntary contraction force (MVC). LMN function was measured by tetanic force, twitch force, and the amplitude of the compound muscle action potential. UMN function was measured by the speed of rapid foot taps, the maximum rate of rise of voluntary force, and the central activation ratio [CAR = MVC/(MVC + superimposed tetanic force)]. The results suggest that (1) LMN loss appears to be the primary cause of progressive weakness in ALS; while (2) UMN impairment in ALS leads to slowing of contraction speed and rapid movements, and modest decreases in central activation; and (3) during 6 months of progression, LMN changes were greater than UMN changes.

Muscle high-energy phosphates in central nervous system disorders. The phosphorus MRS experience

Phosphorus magnetic resonance spectroscopy (MRS) was used to study muscle phosphates metabolism in several brain disorders. Those with primary mitochondrial encephalomyopathies showed the typical pattern of impaired oxidative metabolism at rest and during recovery after exercise. In migraine, Parkinson's disease and alternating hemiplegia muscle MRS observations lend support to a possible mitochondrial dysfunction. Similar observations in multiple sclerosis are probably the result of secondary deconditioning. In post polio syndrome and in some of the hereditary ataxias, elevated intracellular inorganic phosphates may be the result of another, yet unknown, metabolic impairment. Thus, muscle phosphate metabolism may be altered in various central nervous system (CNS) disorders by different metabolic impairments. All these possibilities should be taken into account when evaluating MRS results in brain diseases.

Strength, skeletal muscle composition, and enzyme activity in multiple sclerosis

This study examined functional, biochemical, and morphological characteristics of skeletal muscle in nine multiple sclerosis (MS) patients and eight healthy controls in an effort to ascertain whether intramuscular adaptations could account for excessive fatigue in this disease. Analyses of biopsies of the tibialis anterior muscle showed that there were fewer type I fibers (66 +/- 6 vs. 76 +/- 6%), and that fibers of all types were smaller (average downward arrow26%) and had lower succinic dehydrogenase (SDH; average downward arrow40%) and SDH/alpha-glycerol-phosphate dehydrogenase (GPDH) but not GPDH activities in MS vs. control subjects, suggesting that muscle in this disease is smaller and relies more on anaerobic than aerobic-oxidative energy supply than does muscle of healthy individuals. Maximal voluntary isometric force for dorsiflexion was associated with both average fiber cross-sectional area (r = 0.71, P = 0.005) and muscle fat-free cross-sectional area by magnetic resonance imaging (r = 0.80, P < 0. 001). Physical activity, assessed by accelerometer, was associated with average fiber SDH/GPDH (r = 0.78, P = 0.008). There was a tendency for symptomatic fatigue to be inversely associated with average fiber SDH activity (r = -0.57, P = 0.068). The results of this study suggest that the inherent characteristics of skeletal muscle fibers per se and of skeletal muscle as a whole are altered in the direction of disuse in MS. They also suggest that changes in skeletal muscle in MS may significantly affect function.

Central motor drive is increased during voluntary muscle contractions in multiple sclerosis

To test the hypothesis that central motor drive is increased during voluntary contractions in multiple sclerosis (MS) patients, we recorded the surface electromyogram (EMG) and force from the tibialis anterior muscle during isometric dorsiflexion in 14 MS and 18 control subjects. Measurements were obtained during contractions at 10-100% of maximal voluntary contraction (MVC), incremented by 10% MVC. Integrated EMG (% maximum) was elevated in MS compared to controls from 10 to 70% MVC (pairwise, P < 0.05; main effect, P=0.001). MS severity (Expanded Disability Status Scale) was highly correlated to the individual slopes of the EMG/force relationship (r=-0.87, P < 0.001). We conclude that central motor drive in MS is increased throughout a large range of submaximal contractions and that this increase is associated with overall disease severity.

Quantitation of lower physical activity in persons with multiple sclerosis

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system that often affects the motor system. We tested the hypothesis that physical activity was lower in a group of 17 MS patients (mean +/- SD; age = 46 +/- 6 yr, 11 females, 6 males) compared with 15 healthy sedentary control subjects (age = 44 +/- 7 yr, 9 females, 6 males). Physical activity was measured with a three-dimensional accelerometer and with an activity questionnaire for 7 d. Vector magnitude values from the accelerometer for the MS and sedentary control subjects were 121,027 +/- 59,336 and 185,892 +/- 60,566 arbitrary units/day, respectively (P = 0.01). Estimated energy expenditure values derived from the questionnaire were 35.9 +/- 3.0 and 36.2 +/- 4.1 Kcal.kg-1.d-1 (NS), respectively. Thus, when measured directly with an accelerometer, activity was lower in MS compared with sedentary control subjects. The data also suggest that the accelerometer was more sensitive than the questionnaire for detecting differences in activity between two relatively sedentary populations, including one with neurologic disease.

Serum carnitine and disabling fatigue in multiple sclerosis

The serum concentrations of total, free and acylcarnitine were compared in 25 patients with multiple sclerosis (MS) and among age- and sex-matched normal controls by the new enzymatic cycling method in order to clarify whether the fatigue in MS might be due to possible carnitine-related fatty acid metabolic abnormalities in the mitochondria of skeletal muscles. Patients with MS were divided into those with and those without excessive fatigue. Levels of total and free carnitine were not significantly different between MS patients and normal controls. Levels of acylcarnitine, whose decrease in chronic fatigue syndrome has been reported, were also similar between MS patients and normal controls. There was no difference in these carnitine levels between MS patients with and without excessive fatigue. We argue that acylcarnitine deficiency and fatty acid metabolic dysfunction in mitochondria are not relevant to the excessive fatigue in patients with MS, and further explanatory investigations are to be sought.

Central fatigue assessed by transcranial magnetic stimulation

Central fatigue is a subjective phenomenon which can be examined using transcranial magnetic stimulation (TMS). To assess central fatigue, we compared TMS and peripheral electrical stimulations in patients with central nervous system (CNS) lesions and controls before and after an exhaustive task. The recovery times of motor evoked potential (MEP) amplitudes were significantly prolonged in the patient group whereas the recovery of F waves and compound muscle action potentials showed no significant changes. The results indicate that fatigue cannot be attributed either to intramuscular processes or to reduced spinal excitability, but reflects a supraspinal, probably cortical phenomenon. The measurement of MEP recovery times proved to be a simple and objective tool for the assessment of fatigue and for the differentiation between healthy controls and patients with CNS lesions.

Quantitation of central activation failure during maximal voluntary contractions in humans

Muscle fatigue or neuromuscular disease may result in central activation failure during maximal voluntary contractions (MVCs). Superimposition of an electrically stimulated contraction during an MVC has been used to detect central activation failure. To determine the most sensitive means of quantitating central activation failure using this technique, we compared the increment in isometric force from single, double, and high-frequency trains (50 Hz, 500 or 1000 ms) of stimuli of the peroneal nerve imposed during three separate MVCs of the dorsiflexor muscles. Completeness of activation was quantitated with the central activation ratio (CAR) = MVC/(MVC + stimulated force). Comparisons were made of the CARs of three groups of subjects during the three stimulation conditions: 7 healthy subjects, 13 patients with amyotrophic lateral sclerosis, and 5 healthy subjects after fatiguing exercise. For all three groups, the CAR was significantly lower during the train of stimuli condition (means = 0.76-0.89) compared with either the single or double stimuli conditions (means = 0.96-1.00). The results suggest that a superimposed high-frequency train of stimuli is a more sensitive indicator of central activation failure during isometric MVCs compared with either the superimposed single or double stimuli methods.

Evidence of an abnormal intramuscular component of fatigue in multiple sclerosis

The goals of this study were to investigate muscle fatigue in patients with multiple sclerosis (MS), and to determine the relationships between muscle fatigue, clinical status, and perceived fatigue. The fatigability of the anterior tibial muscle was quantitated in patients and controls during 9 min of intermittent stimulation (used to eliminate central sources of muscle fatigue). During exercise, the decline in tetanic force, phosphocreatine, and intracellular pH was greater in patients than in controls. The compound muscle action potential amplitude did not decrease during exercise, indicating that there was no failure of neuromuscular transmission during fatigue. Thus, the excessive fatigue in MS developed from sources beyond the muscle membrane. Following exercise, the recovery of tetanic force was delayed in patients (a pattern that suggests abnormal excitation-contraction coupling), whereas the recovery of metabolites was complete in both groups. Muscular fatigue was correlated with clinical disability but not with perceived fatigue. These results suggests that fatigue in MS has both central (perception, upper motor neuron dysfunction) and peripheral (impaired metabolism and excitation-contraction coupling) components.