Postexercise phosphocreatine resynthesis is slowed in multiple sclerosis

Effects of photobiomodulation therapy on muscle function in individuals with multiple sclerosis

BACKGROUND

In people with multiple sclerosis (pwMS), muscle fatigue and weakness are common issues that can interfere with daily activities. Photobiomodulation therapy (PBMT), comprising light in a 600-1100 nm bandwidth, is a low-level laser therapy thought to improve muscle performance in non-disease populations, in part, by improving mitochondrial function and thus, might be beneficial in pwMS. Given this potential, we aimed to investigate the effects of PBMT on muscle performance in pwMS, both in the short-term and over an extended period.

METHODS

This study consisted of two parts with a randomized double-blind crossover design. In study I, muscle function was assessed in four sessions before and after PBMT in ambulatory pwMS (N = 17, F = 14) as follows: maximal voluntary contraction (MVC) and muscle fatigue of the right tibialis anterior (TA) muscle was compared at baseline and following a two-min submaximal fatiguing contraction. Then, PBMT was administered to the belly of TA muscle at different doses of energy of an active device (40 J, 80 J, 120 J) or placebo. The muscle function assessment was then repeated.

OUTCOME VARIABLES

muscle force recovery (%), muscle fatigue (%). Statistical tests included McNemar's exact test, Wilcoxon signed-rank test, and the Friedman test. In study II, a subgroup from study I (N = 12, F = 11) received individualized doses (i.e., best dose-effect observed in study I) of active, or placebo PBMT, which was administered on the TA muscle for two weeks. Muscle function assessments were performed pre- and post-PBMT in four sessions similar to study I.

OUTCOME VARIABLES

Baseline strength (N), endurance time (s), and muscle fatigue (%). The Wilcoxon signed-rank test was used for statistical analysis. Values are reported as mean (SD).

RESULTS

In study I, participants who received a high dose of PBMT showed significant improvement in force recovery (101.89 % (13.55 %)) compared to the placebo group (96.3 % (18.48 %); p = 0.03). Muscle fatigue did not significantly improve with either active PBMT or placebo. In study II, active PBMT resulted in a significant improvement in muscle strength compared to both the baseline (pre-PBMT = 162.70 N (37.52 N); post-PBMT = 185.56 N (33.95 N); p = 0.01) and the placebo group (active PBMT: mean-change = 22.87 N (23.67 N); placebo: mean-change = -4.12 N (31.95 N); p = 0.02). Endurance time and muscle fatigue did not show significant improvement with either active PBMT or placebo.

CONCLUSION

Our findings suggest that an individualized dose of PBMT might improve muscle performance, including force recovery and strength in individuals with mild-moderate MS. Therefore, PBMT might be a novel therapeutic modality, either as a standalone treatment or in combination with other interventions, to improve muscle performance in pwMS.

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.

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.

Altered muscle oxidative phenotype impairs exercise tolerance but does not improve after exercise training in multiple sclerosis

BACKGROUND

Patients with multiple sclerosis (MS) experience reduced exercise tolerance that substantially reduces quality of life. The mechanisms underpinning exercise intolerance in MS are not fully clear. This study aimed to determine the contributions of the cardiopulmonary system and peripheral muscle in MS-induced exercise intolerance before and after exercise training.

METHODS

Twenty-three patients with MS (13 women) and 20 age-matched and sex-matched healthy controls (13 women) performed a cardiopulmonary exercise test. Muscle fibre type composition, size, succinate dehydrogenase (SDH) activity, capillarity, and gene expression and proteins related to mitochondrial density were determined in vastus lateralis muscle biopsies. Nine MS patients (five women) were re-examined following a 12 week exercise training programme consisting of high-intensity cycling interval and resistance training.

RESULTS

Patients with MS had lower maximal oxygen uptake compared with healthy controls (V̇O_2peak , 25.0 ± 8.5 vs. 35.7 ± 6.4 mL/kg/min, P < 0.001). The lower gas exchange threshold (MS: 14.5 ± 5.5 vs. controls: 19.7 ± 2.9 mL/kg/min, P = 0.01) and slope of V̇O₂ versus work rate (MS: 9.5 ± 1.7 vs. controls: 10.8 ± 1.1 mL/min/W, P = 0.01) suggested an intramuscular contribution to exercise intolerance in patients with MS. Muscle SDH activity was 22% lower in MS (P = 0.004), and strongly correlated with several indices of whole-body exercise capacity in MS patients (e.g. V̇O_2peak , Spearman's ρ = 0.81, P = 0.002), but not healthy controls (ρ = 0.24, P = 0.38). In addition, protein levels of mitochondrial OXPHOS complexes I (-40%, P = 0.047) and II (-45%, P = 0.026) were lower in MS patients versus controls. Muscle capillary/fibre ratio correlated with V̇O_2peak in healthy controls (ρ = 0.86, P < 0.001) but not in MS (ρ = 0.35, P = 0.22), and did not differ between groups (1.41 ± 0.30 vs. 1.47 ± 0.38, P = 0.65). Expression of genes involved in mitochondrial function, such as PPARA, PPARG, and TFAM, was markedly reduced in muscle tissue samples of MS patients (all P < 0.05). No differences in muscle fibre type composition or size were observed between groups (all P > 0.05). V̇O_2peak increased by 23% following exercise training in MS (P < 0.001); however, no changes in muscle capillarity, SDH activity, gene or protein expression were observed (all P > 0.05).

CONCLUSIONS

Skeletal muscle oxidative phenotype (mitochondrial complex I and II content, SDH activity) is lower in patients with MS, contributing to reduced exercise tolerance. However, skeletal muscle mitochondria appeared resistant to the beneficial effects of exercise training, suggesting that other physiological systems, at least in part, drive the improvements in exercise capacity following exercise training in MS.

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.

The potential roles of amino acids and their major derivatives in the management of multiple sclerosis

Recently, we reviewed the important role of carbohydrates and lipids metabolism in different clinical aspects of multiple sclerosis (MS) disease. In the current paper, we aimed to review the contribution of amino acids and their major derivatives to different clinical outcomes of the disease, including etiology, pathogenesis, diagnosis, prognosis, and treatment. In this line, Thr (threonine), Phe (phenylalanine), Glu (glutamate), Trp (tryptophan), and Sero (serotonin) are the main examples of biomolecules that have been suggested for MS therapy. It has been concluded that different amino acids and their derivatives might be considered prominent tools for the clinical management of MS disease.

Oxygen Cost of Walking in People With Multiple Sclerosis and Its Association With Fatigue: A Systematic Review and Meta-analysis

BACKGROUND

This systematic review and meta-analysis aimed to compare the oxygen cost of walking in individuals with multiple sclerosis (MS) and controls and to assess the relationship between oxygen cost of walking and fatigue in individuals with MS.

METHODS

Four databases (CINAHL, MEDLINE, ProQuest, Web of Science) were searched up to September 2020. Studies were included if they recruited adults with MS and either compared oxygen cost of walking in those with MS and a control population or determined the relationship between oxygen cost of walking and fatigue. Meta-analysis of the standardized mean difference in oxygen cost of walking between individuals with MS and controls was performed.

RESULTS

Nine studies were included in this review, of which 7 compared oxygen cost of walking in individuals with MS (n = 176) and controls (n = 142) and 4 investigated the relationship between oxygen cost of walking and fatigue. Meta-analysis revealed that individuals with MS (with predominantly mild-to-moderate disability) had a significantly higher oxygen cost of walking compared with controls (standardized mean difference = 2.21, 95% CI = 0.88 to 3.54, P = .001). In addition, 3 studies found a significant yet weak positive association between oxygen cost of walking and fatigue.

CONCLUSIONS

Individuals with MS expend more energy when walking compared with controls. This increase in energy expenditure may contribute to the development of fatigue, as some studies found that higher oxygen costs of walking were associated with greater fatigue. Future studies should investigate whether reducing energy expenditure during movement improves fatigue.

Forearm muscle mitochondrial capacity and resting oxygen uptake: Relationship to symptomatic fatigue in persons with multiple sclerosis

Background

Mitochondrial dysfunction has been implicated in the pathogenesis of multiple sclerosis (MS). Whether mitochondrial alterations are a function of ambulatory dysfunction or are of a non-ambulatory systemic nature is unclear.

Objective

To compare oxidative capacity, and rest muscle oxygen consumption (mVO₂) in the upper limb of persons with multiple sclerosis (PwMS) to a control group (CON), whereby an upper limb would be comparatively independent of ambulation or deconditioning.

Methods

Near infra-red spectroscopy was used to measure oxidative capacity of the wrist flexors in PwMS (n = 16) and CON (n = 13). Oxidative capacity was indicated by the time constant (TC) of mVO₂ recovery following brief wrist flexion contractions. Measurements included well-being, depression, symptomatic fatigue, disability, handgrip strength, cognition, and functional endurance. Analysis was by T-tests and Pearson correlations with p ≤ 0.05. Data are mean (SD).

Results

TC of mVO₂ recovery was slower in PwMS (MS = 47(14) sec, CON = 36(11) sec; p = 0.03). No significant correlations were found between oxidative capacity and any other measures. Rest mVO₂ was not different between groups, but correlated with symptomatic fatigue (r = 0.694, p = 0.003) and strength (0.585, p = 0.017) in PwMS.

Conclusion

Oxidative capacity was lower in the wrist flexors of PwMS, possibly indicating a systemic component of the disease. Within PwMS, rest mVO₂ was associated with symptomatic fatigue.

Brain and Muscle: How Central Nervous System Disorders Can Modify the Skeletal Muscle

It is widely known that nervous and muscular systems work together and that they are strictly dependent in their structure and functions. Consequently, muscles undergo macro and microscopic changes with subsequent alterations after a central nervous system (CNS) disease. Despite this, only a few researchers have addressed the problem of skeletal muscle abnormalities following CNS diseases. The purpose of this review is to summarize the current knowledge on the potential mechanisms responsible for changes in skeletal muscle of patients suffering from some of the most common CSN disorders (Stroke, Multiple Sclerosis, Parkinson’s disease). With this purpose, we analyzed the studies published in the last decade. The published studies show an extreme heterogeneity of the assessment modality and examined population. Furthermore, it is evident that thanks to different evaluation methodologies, it is now possible to implement knowledge on muscle morphology, for a long time limited by the requirement of muscle biopsies. This could be the first step to amplify studies aimed to analyze muscle characteristics in CNS disease and developing rehabilitation protocols to prevent and treat the muscle, often neglected in CNS disease.

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.

Effect of High-Intensity Exercise on Multiple Sclerosis Function and Phosphorous Magnetic Resonance Spectroscopy Outcomes

PURPOSE

We determined if a high-intensity aerobic exercise program would be safe, improve expected fitness and clinical outcomes, and alter exploratory phosphorous magnetic resonance spectroscopy (P MRS) outcomes in persons with multiple sclerosis (PwMS).

METHODS

This open-label prospective pilot study compared two cohorts of ambulatory PwMS matched for age, sex and V˙O2max. Cohorts underwent 8 wk of high-intensity aerobic exercise (MS-Ex, n = 10) or guided stretching (MS-Ctr, n = 7). Aerobic exercise consisted of four 30-min sessions per week while maintaining ≥70% maximal HR. Changes in cardiorespiratory fitness, clinical outcomes, and P MRS of tibialis anterior (TA) muscle and brain were compared. Cross-sectional P MRS comparisons were made between all MS participants and a separate matched healthy control population.

RESULTS

The MS-Ex cohort achieved target increases in V˙O2max (mean, +12.7%; P = <0.001, between-group improvement, P = 0.03). One participant was withdrawn for exercise-induced syncope. The MS-Ex cohort had within-group improvements in fat mass (-5.8%; P = 0.04), lean muscle mass (+2.6%; P = 0.02), Symbol Digit Modalities Test (+15.1%; P = 0.04), and cognitive subscore of the Modified Fatigue Impact Scale (-26%; P = 0.03), whereas only the physical subscore of the Modified Fatigue Impact Scale improved in MS-Ctr (-16.1%; P = 0.007). P MRS revealed significant within-group increases in MS-Ex participants in TA rate constant of phosphocreatine (PCr) recovery (+31.5%; P = 0.03) and adenosine triphosphate/PCr (+3.2%; P = 0.01), and near significant between-group increases in TA PCr recovery rate constant (P = 0.05) but no significant changes in brain P MRS after exercise. Cross-sectional differences existed between MS and healthy control brain PCr/inorganic phosphate (4.61 ± 0.44, 3.93 ± 0.19; P = 0.0019).

CONCLUSIONS

High-intensity aerobic exercise in PwMS improved expected cardiorespiratory and clinical outcomes but provoked one serious adverse event. The P MRS may serve to explore underlying mechanisms by which aerobic exercise exerts cerebral benefits.

Effects of Treadmill Training on Muscle Oxidative Capacity and Endurance in People with Multiple Sclerosis with Significant Walking Limitations

Background

Exercise can improve muscle function and mobility in people with multiple sclerosis (MS). However, the effects of exercise training on skeletal muscle oxidative capacity and endurance in people with MS remain unclear, and few studies have evaluated muscle plasticity in people with MS who have moderate-to-severe disability. The present study evaluated the effects of treadmill training on muscle oxidative capacity and muscle endurance and examined the relationship to walking function in people with MS who have moderate-to-severe disability.

Methods

Six adults (mean ± SD age, 50 ± 4.9 years) with MS (Expanded Disability Status Scale score, 6.0-6.5) performed treadmill training for 24 minutes approximately twice per week for approximately 8 weeks (16 sessions total) using an antigravity treadmill system. The following measures were taken before and after the intervention phase: muscle oxidative capacity in the medial gastrocnemius using near-infrared spectroscopy after 15 to 20 seconds of electrical stimulation; muscle endurance in the medial gastrocnemius using accelerometer-based mechanomyography during 9 minutes of twitch electrical stimulation in three stages (3 minutes per stage) of increasing frequency (2, 4, and 6 Hz); and walking function using the 2-Minute Walk Test.

Results

Mean ± SD muscle oxidative capacity increased from 0.64 ± 0.19 min^-1 to 1.08 ± 0.52 min^-1 (68.2%). Mean ± SD muscle endurance increased from 80.9% ± 15.2% to 91.5% ± 4.8% at 2 Hz, from 56.3% ± 20.1% to 76.6% ± 15.8% at 4 Hz, and from 29.2% ± 13.1% to 53.9% ± 19.4% at 6 Hz of stimulation in the gastrocnemius. There were no significant improvements in walking function.

Conclusions

Treadmill training can improve muscle oxidative capacity and endurance in people with MS who have moderate-to-severe levels of disability.

Hamstrings and Quadriceps Muscles Function in Subjects with Prior ACL Reconstruction Surgery

BACKGROUND

As the knee joint is a common site for injury among younger people, the purpose of this study was to measure the skeletal muscle endurance and strength on people with prior anterior cruciate ligament (ACL) knee reconstruction surgery.

METHOD

Young healthy female subjects who reported having knee reconstruction surgery more than one-year prior were tested. The skeletal muscle endurance index (EI) of the hamstrings and quadriceps muscles was determined as the decline in the specific muscle acceleration in response to 2 Hz, 4 Hz, and 6 Hz electrical stimulation. Maximal isometric muscle strength (MVC) was measured in the hamstrings and quadriceps muscles.

RESULTS

The hamstrings muscles in the injured leg had less endurance than the non-injured leg at 6 Hz stimulation (55.5 ± 13.2% versus 78.0 ± 13.3%, p < 0.01). Muscle endurance was not reduced in the quadriceps muscles in the injured leg compared to the non-injured leg at 6 Hz stimulation (78.0 ± 13.3% versus 80.3 ± 10.0%, p = 0.45). There were no differences in MVC between the injured and non-injured legs for either the hamstrings (p = 0.20) or quadriceps muscles (p = 0.67).

CONCLUSIONS

Muscle endurance was reduced in the hamstrings muscles at least one-year post injury, while hamstrings strength was recovered. Reduced hamstrings muscle endurance could be a result of lack of endurance training during rehabilitation. This may contribute to re-injury in the muscle, even in people who have recovered muscle strength.

Effects of lipoic acid on walking performance, gait, and balance in secondary progressive multiple sclerosis

BACKGROUND

Gait and balance impairment is common in secondary progressive multiple sclerosis (SPMS). Lipoic acid (LA), an over-the-counter antioxidant, is effective in MS animal models and may improve walking speed, but effects on mobility are unreported.

OBJECTIVE

Examine the effects of 1200 mg daily oral dose of LA versus placebo (PLA) on gait and balance in a 2-year, randomized, double-blind pilot study.

METHODS

134 participants were screened for eligibility before assignment to LA (n = 28) or PLA (n = 26). Included here were, 21 participants with SPMS who took LA (N = 11) or PLA (N = 10) capsules for 2 years (enrolled May 2, 2011 - August 14, 2015) and completed all tasks without the use of an assistive device. Participants completed the Timed Up and Go (TUG) and quiet standing tasks every 6 months while wearing inertial sensors (APDM Opals) to quantify mobility.

RESULTS

LA had a medium effect on time to complete TUG at 2 years (g = 0.51; 95% CI = -0.35, 1.38). In a subset of 18 participants with less disability (EDSS < 6, no use of ambulatory device), turning time was significantly shorter with LA (p =  0.048, Δ= 0.48 s). No differences in balance metrics were found between groups.

CONCLUSIONS

LA had an effect on walking performance in people with SPMS, particularly in those with lower baseline disability.

TRIAL REGISTRATION

Lipoic Acid for Secondary Progressive Multiple Sclerosis https://clinicaltrials.gov/ct2/show/NCT01188811?term=spain+lipoic+acid&rank=1 NCT0118881.

Case Report: Effect of Antigravity Treadmill Training on Muscle Oxidative Capacity, Muscle Endurance, and Walking Function in a Person with Multiple Sclerosis

Background

Exercise training can improve skeletal muscle metabolism in persons with multiple sclerosis (MS). However, quantification of exercise-mediated improvements in muscle metabolism has been limited, particularly in people with high levels of disability. We evaluated the effect of 9 weeks of antigravity treadmill training on muscle oxidative capacity and muscle endurance and assessed the relationship to walking function in a person with MS.

Methods

One person with MS (Expanded Disability Status Scale score, 6.5) performed treadmill training for 24 minutes approximately twice weekly for 9 weeks (16 sessions) using an antigravity treadmill system. Before and after the intervention phase, we measured muscle oxidative capacity in the medial gastrocnemius using near-infrared spectroscopy after 15 to 20 seconds of electrical stimulation; muscle endurance in the medial gastrocnemius using accelerometer-based mechanomyography during 9 minutes of twitch electrical stimulation in three stages (3 minutes per stage) of increasing frequency (2, 4, and 6 Hz); muscle strength (plantarflexion) using a maximal voluntary contraction; and walking function using the Timed 25-Foot Walk test and the 2-Minute Walk Test.

Results

Muscle oxidative capacity increased from 0.73 min^-1 to 1.08 min^-1 (48%). Muscle endurance increased from 75.9% to 84.0% at 2 Hz, from 67.8% to 76.2% at 4 Hz, and from 13.5% to 44.7% at 6 Hz. Maximal voluntary contraction decreased by 0.68 kg (15%), Timed 25-Foot Walk test speed decreased by 0.19 ft/s (20%), and 2-Minute Walk Test distance increased by 65 m (212%).

Conclusions

Muscle oxidative capacity and muscle endurance, as well as walking function, improved in a person with MS after training on an antigravity treadmill.

Muscle carnosine in experimental autoimmune encephalomyelitis and multiple sclerosis

BACKGROUND

Muscle carnosine is related to contractile function (Ca⁺⁺ handling) and buffering of exercise-induced acidosis. As these muscular functions are altered in Multiple Sclerosis (MS) it is relevant to understand muscle carnosine levels in MS.

METHODS

Tibialis anterior muscle carnosine was measured in an animal MS model (EAE, experimental autoimmune encephalomyelitis, n = 40) and controls (CON, n = 40) before and after exercise training (EAE_EX, CON_EX, 10d, 1 h/d, 24 m/min treadmill running) or sedentary conditions (EAE_SED, CON_SED). Human m. vastus lateralis carnosine of healthy controls (HC, n = 22) and MS patients (n = 24) was measured.

RESULTS

EAE muscle carnosine levels were decreased (p < .0001) by ~ 40% to ~ 64% at 10d and 17d following EAE induction (respectively) regardless of exercise (p = .823). Similarly, human MS muscle carnosine levels were decreased (- 25%, p = .03).

CONCLUSION

Muscle carnosine concentrations in an animal MS model and MS patients are substantially reduced. In EAE exercise therapy does not restore this.

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.

The Assessment of Motor Fatigability in Persons With Multiple Sclerosis: A Systematic Review

Background. Persons with multiple sclerosis (PwMS) are often characterized by increased motor fatigability, which is a performance change on an objectively measured criterion after any type of voluntary muscle contractions. This review summarizes the existing literature to determine which protocols and outcome measures are best to detect or study motor fatigability and the underlying mechanisms in MS. Methods. Two electronic databases, PubMed and Web of Science, were searched for relevant articles published until August 2016 with a combination of multiple sclerosis, fatigability, muscle fatigue, and motor fatigue. Results. A total of 48 articles were retained for data extraction. A variety of fatigability protocols were reported; protocols showed differences in type (isometric vs concentric), duration (15 to 180 s), and number of contractions (fixed or until exhaustion). Also, 12 articles reported motor fatigability during functional movements, predominantly assessed by changes in walking speed; 11 studies evaluated the mechanisms underlying motor fatigability, using additional electrical nerve or transcranial magnetic stimulation. Three articles reported psychometrics of the outcomes. Conclusions. The disparity of protocols and outcome measures to study different aspects of motor fatigability in PwMS impedes direct comparison between data. Most protocols use maximal single-joint isometric contractions, with the advantage of high standardization. Because there is no head-to-head comparison of the different protocols and only limited information on psychometric properties of outcomes, there is currently no gold standard to assess motor fatigability. The disability level, disease phenotype, and studied limb may influence the assessment of motor fatigability in PwMS.

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.

Skeletal muscle mitochondrial capacity in people with multiple sclerosis

Background

People with multiple sclerosis (MS) have functional disability and may have reduced muscle mitochondrial capacity.

Objective

The objective of this paper is to measure muscle mitochondrial capacity of leg muscles using near-infrared spectroscopy (NIRS) and compare to functional status.

Materials and methods

People with MS (n = 16) and a control (CON) group (n = 9) were evaluated for 25-ft walk time. Mitochondrial capacity of both gastrocnemius muscles were measured with NIRS as the rate of recovery of oxygen consumption in after exercise.

Results

Mitochondrial capacity was lower in the MS group compared to the CON group (rate constants: 1.13 ± 0.29 vs. 1.68 ± 0.37 min⁻¹, p < 0.05). There was a tendency for people with MS who used assistive devices to have lower mitochondrial capacity in the weaker leg (p = 0.07).

Conclusion

NIRS measurements of mitochondrial capacity suggest a 40% deficit in people with MS compared to CONs and this may contribute to walking disability.

In vivo mitochondrial function in aging skeletal muscle: capacity, flux, and patterns of use

Because of the fundamental dependence of mammalian life on adequate mitochondrial function, the question of how and why mitochondria change in old age is the target of intense study. Given the importance of skeletal muscle for the support of mobility and health, this question extends to the need to understand mitochondrial changes in the muscle of older adults, as well. We and others have focused on clarifying the age-related changes in human skeletal muscle mitochondrial function in vivo. These changes include both the maximal capacity for oxidative production of energy (ATP), as well as the relative use of mitochondrial ATP production for powering muscular activity. It has been known for nearly 50 yr that muscle mitochondrial content is highly plastic; exercise training can induce an ∼2-fold increase in mitochondrial content, while disuse has the opposite effect. Here, we suggest that a portion of the age-related changes in mitochondrial function that have been reported are likely the result of behavioral effects, as physical activity influences have not always been accounted for. Further, there is emerging evidence that various muscles may be affected differently by age-related changes in physical activity and movement patterns. In this review, we will focus on age-related changes in oxidative capacity and flux measured in vivo in human skeletal muscle.

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.

Effects of aerobic and strength exercise on motor fatigue in men and women with multiple sclerosis: a randomized controlled trial

Objective: To investigate the effects of aerobic and strength exercise on motor fatigue of knee flexor and extensor muscles in subjects with multiple sclerosis (MS).

Design: A randomized controlled trial.

Setting: At Masku Neurological Rehabilitation Centre, Masku, and the Social Insurance Institution, Research Department, Turku, Finland.

Subjects: Ninety-five MS patients with mild to moderate disability were randomized into exercise group (n = 47) and a control group (n = 48).

Intervention: Participants in the exercise group attended in a supervised exercise period of three weeks, which was followed by a home exercise programme lasting for 23 weeks. Patients in the control group continued with their normal living.

Outcome measures: Motor fatigue of knee flexor and extensor muscles was measured during a static 30-s maximal sustained muscle contraction. The decline in force (Nm) during the 30 s was recorded, and a fatigue index (FI) was calculated. Subjective fatigue was measured by using the Fatigue Severity Scale (FSS). The Ambulatory Fatigue Index (AFI) was calculated on the basis of a 500-m walking test. Assessment took place at baseline, at the third week (not for the control group) and at the 26th week. All outcome variables were analysed, men and women together, and some interesting contrasts were analysed by gender.

Results: Associations were observed with changes in extension FI and Expanded Disability Status Scale (EDSS) score and mean extension torque (Nm), but not with changes in FI and aerobic or strength exercise activity, mean AFI, mean FSS or in mean knee flexion torque. AFI was decreased in all subject groups (p = 0.007). Motor fatigue was reduced in knee flexion (p = 0.0014) and extension (ns) among female but not in male exercisers after six months of exercise. The exercise activity of women was 25% higher than that of the men.

Conclusions: Six months of exercise reduced motor fatigue in women, but not in men.

Altered signaling for mitochondrial and myofibrillar biogenesis in skeletal muscles of patients with multiple sclerosis

Patients with multiple sclerosis (pwMS) experience muscle weakness and lowered muscle oxidative capacity. To explore the etiology for the development of such muscle phenotype we studied skeletal muscle adenosine monophosphate (AMP)-activated protein kinase phosphorylation (phospho-AMPKα, governing mitochondrial biogenesis) and mammalian target of rapamycin phosphorylation (phospho-mTOR, governing myofibrillar biogenesis) in pwMS. After assessment of body composition, muscle strength, exercise tolerance, and muscle fiber type, muscle phospho-AMPKα and phospho-mTOR were assessed in 14 pwMS and 10 healthy controls (part 1). Next, an endurance exercise bout was executed by 9 pwMS and 7 healthy subjects, with assessment of changes in muscle phospho-AMPKα and phospho-mTOR (part 2). Increased basal muscle phospho-AMPKα and phospho-mTOR were present in MS (P < 0.01) and independently related to MS. Correlations between muscle phospho-AMPKα or phospho-mTOR and whole-body fat mass, peak oxygen uptake, and expanded disability status scale (P < 0.05) were found. After endurance exercise muscle phospho-AMPKα and phospho-mTOR remained increased in pwMS (P < 0.01). Muscle signaling cascades for mitochondrial and myofibrillar biogenesis are altered in MS and related to the impairment and disability level. These findings indicate a link between muscle signaling cascades and the level of disability and impairment, and thus may open a new area for the development of novel therapies for peripheral muscle impairment in MS.

Pilot study: evaluation of the effect of functional electrical stimulation cycling on muscle metabolism in nonambulatory people with multiple sclerosis

OBJECTIVE

To investigate the changes in muscle oxygen consumption (mV˙O2) using near-infrared spectroscopy (NIRS) after 4 weeks of training with functional electrical stimulation (FES) cycling in nonambulatory people with multiple sclerosis (MS).

DESIGN

Four-week before-after trial to assess changes in mV˙O2 after an FES cycling intervention.

SETTING

Rehabilitation hospital.

PARTICIPANTS

People (N=8; 7 men, 1 women) from a volunteer/referred sample with moderate to severe MS (Expanded Disability Status Scale score>6.0).

INTERVENTION

Participants cycled 30 minutes per session, 3d/wk for 4 weeks or a total of 12 sessions.

MAIN OUTCOME MEASURES

mV˙O2 of the right vastus lateralis muscle was measured with NIRS before and within 1 week after the intervention. Six bouts of 15-second electrical stimulation increasing from 2 to 7Hz were used to activate the muscle. mV˙O2 was assessed by analyzing the slope of the NIRS oxygen signal during a 10-second arterial occlusion after each electrical stimulation bout.

RESULTS

Significant FES training by electrical stimulation frequency level interaction was observed (P=.031), with an average increase in mV˙O2 of 47% across frequencies with a main effect of training (P=.047).

CONCLUSIONS

FES cycling for 4 weeks improved mV˙O2, suggesting that FES cycling is a potential therapy for improving muscle health in people with MS who are nonambulatory.

A cross-validation of near-infrared spectroscopy measurements of skeletal muscle oxidative capacity with phosphorus magnetic resonance spectroscopy

The purpose of this study was to cross-validate measurements of skeletal muscle oxidative capacity made with near-infrared spectroscopy (NIRS) measurements to those made with phosphorus magnetic resonance spectroscopy ((31)P-MRS). Sixteen young (age = 22.5 ± 3.0 yr), healthy individuals were tested with both (31)P-MRS and NIRS during a single testing session. The recovery rate of phosphocreatine was measured inside the bore of a 3-Tesla MRI scanner, after short-duration (∼10 s) plantar flexion exercise as an index of skeletal muscle oxidative capacity. Using NIRS, the recovery rate of muscle oxygen consumption was also measured using repeated, transient arterial occlusions outside the MRI scanner, after short-duration (∼10 s) plantar flexion exercise as another index of skeletal muscle oxidative capacity. The average recovery time constant was 31.5 ± 8.5 s for phosphocreatine and 31.5 ± 8.9 s for muscle oxygen consumption for all participants (P = 0.709). (31)P-MRS time constants correlated well with NIRS time constants for both channel 1 (Pearson's r = 0.88, P < 0.0001) and channel 2 (Pearson's r = 0.95, P < 0.0001). Furthermore, both (31)P-MRS and NIRS exhibit good repeatability between trials (coefficient of variation = 8.1, 6.9, and 7.9% for NIRS channel 1, NIRS channel 2, and (31)P-MRS, respectively). The good agreement between NIRS and (31)P-MRS indexes of skeletal muscle oxidative capacity suggest that NIRS is a valid method for assessing mitochondrial function, and that direct comparisons between NIRS and (31)P-MRS measurements may be possible.

Myalgic encephalomyelitis/chronic fatigue syndrome and encephalomyelitis disseminata/multiple sclerosis show remarkable levels of similarity in phenomenology and neuroimmune characteristics

BACKGROUND

'Encephalomyelitis disseminata' (multiple sclerosis) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) are both classified as diseases of the central nervous system by the World Health Organization. This review aims to compare the phenomenological and neuroimmune characteristics of MS with those of ME/CFS.

DISCUSSION

There are remarkable phenomenological and neuroimmune overlaps between both disorders. Patients with ME/CFS and MS both experience severe levels of disabling fatigue and a worsening of symptoms following exercise and resort to energy conservation strategies in an attempt to meet the energy demands of day-to-day living. Debilitating autonomic symptoms, diminished cardiac responses to exercise, orthostatic intolerance and postural hypotension are experienced by patients with both illnesses. Both disorders show a relapsing-remitting or progressive course, while infections and psychosocial stress play a large part in worsening of fatigue symptoms. Activated immunoinflammatory, oxidative and nitrosative (O+NS) pathways and autoimmunity occur in both illnesses. The consequences of O+NS damage to self-epitopes is evidenced by the almost bewildering and almost identical array of autoantibodies formed against damaged epitopes seen in both illnesses. Mitochondrial dysfunctions, including lowered levels of ATP, decreased phosphocreatine synthesis and impaired oxidative phosphorylation, are heavily involved in the pathophysiology of both MS and ME/CFS. The findings produced by neuroimaging techniques are quite similar in both illnesses and show decreased cerebral blood flow, atrophy, gray matter reduction, white matter hyperintensities, increased cerebral lactate and choline signaling and lowered acetyl-aspartate levels.

SUMMARY

This review shows that there are neuroimmune similarities between MS and ME/CFS. This further substantiates the view that ME/CFS is a neuroimmune illness and that patients with MS are immunologically primed to develop symptoms of ME/CFS.

Effect of creatine supplementation on muscle capacity in individuals with multiple sclerosis

There has been interest in the use of exogenous creatine (Cr) as an adjunct treatment for neurological disorders. Creatine enhances bouts of activity through augmenting phosphocreatine for increased synthesis of ATP; however, multiple sclerosis (MS) individuals suffering from muscle weakness have not been shown to improve muscle work after 5 days of Cr supplementation. This study's purpose was to determine whether the extended duration would increase muscle capacity. In a double-blind, crossover trial, with a 3-week washout period, eleven MS subjects were randomly assigned to either Cr (5 g 4/day, day 1-7: 2.5 g 2/day, day 8-14) or placebo groups for two 14-day periods. Biodex Dynamometer recorded total work and power over three bouts of 30 maximal knee extensions and flexions. Total work was nonsignificant with Cr for knee extension (pretest 1277.7 ± 214.9 J vs. posttest = 1313.14 ± 200.5 J; p = 0.81) and flexion (pretest = 1220.7 ± 200.5 J vs. posttest = 1302.10 J ± 189.64 J; p = 0.93). Creatine did not enhance muscle power in knee extension (p = 0.31; pretest = 82.1 ± 12.7 W vs. posttest = 87.7 ± 12.6 W) or flexion (p = 0.29; pretest = 75.3 ± 12.1 W vs. posttest = 81.2 ± 11.1 W). Therefore, 14 days of Cr supplementation did not improve muscle capacity or habitual fatigue in MS individuals.

A comparison of exercise type and intensity on the noninvasive assessment of skeletal muscle mitochondrial function using near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) can be used to measure muscle oxygen consumption (mVO(2)) using arterial occlusions. The recovery rate of mVO(2) after exercise can provide an index of skeletal muscle mitochondrial function. The purpose of this study was to test the influence of exercise modality and intensity on NIRS measurements of mitochondrial function. Three experiments were performed. Thirty subjects (age: 18-27 yr) were tested. NIRS signals were corrected for blood volume changes. The recovery of mVO(2) after exercise was fit to a monoexponential curve, and a rate constant was calculated (directly related to mitochondrial function). No differences were found in NIRS rate constants for VOL and ES exercises (2.04 ± 0.57 vs. 2.01 ± 0.59 min(-1) for VOL and ES, respectively; P = 0.317). NIRS rate constants were independent of the contraction frequency for both VOL and ES (VOL: P = 0.166 and ES: P = 0.780). ES current intensity resulted in significant changes to the normalized time-tension integral (54 ± 11, 82 ± 7, and 100 ± 0% for low, medium, and high currents, respectively; P < 0.001) but did not influence NIRS rate constants (2.02 ± 0.54, 1.95 ± 0.44, 2.02 ± 0.46 min(-1) for low, medium, and high currents, respectively; P = 0.771). In summary, NIRS measurements of skeletal muscle mitochondrial function can be compared between VOL and ES exercises and were independent of the intensity of exercise. NIRS represents an important new technique that is practical for testing in research and clinical settings.

Slowed Exercise-Onset Vo2 Kinetics During Submaximal Endurance Exercise in Subjects With Multiple Sclerosis

Background. Low physical activity levels in persons with multiple sclerosis (MS) may reduce skeletal muscle oxidative capacity. Rehabilitation strategies might be altered by a measure of capacity that did not require invasive techniques or maximal exercise testing. For this purpose, we measured exercise onset and offset oxygen uptake (Vo2) kinetics during endurance exercise. Objective. This study compared exercise-onset and -offset Vo2 kinetics in mildly affected persons with MS with healthy matched participants. Methods. From 38 MS patients who had a mean Expanded Disability Status Scale of 3.1 and 16 healthy participants, exercise-onset and -offset Vo2 kinetics (mean response time [MRT]) were determined during two 6-minute submaximal bouts of exercise separated by a 6-minute recovery interval. Blood lactate, heart rate, expiratory volume, and Borg ratings of perceived exertion were assessed during exercise and compared between groups. Relationships between clinical characteristics and MRT were assessed. Results. During exercise, blood lactate, heart rate, and expiratory volume did not differ between groups ( P > .05), but exercise-onset MRT was significantly slower in MS versus healthy participants ( P = .007). Exercise-onset MRT was independently related to having MS ( P = .02). Exercise-offset MRT was not different between groups or was independently related to having MS ( P > .05). No independent relationships between clinical characteristics of MS and exercise-onset or -offset MRT were found. Conclusions. Exercise-onset Vo2 kinetics during submaximal endurance exercise are significantly slowed in mildly disabled persons with MS, suggesting low skeletal muscle oxidative capacity. Using mean response time testing, rehabilitation interventions for this reduction in exercise capacity can be assessed and targeted.

Postmaximal contraction blood volume responses are blunted in obese and type 2 diabetic subjects in a muscle-specific manner

The purpose of this study was to determine whether there are differences in postisometric contraction blood volume and oxygenation responses among groups of type 2 diabetes mellitus (T2DM), obese, and lean individuals detectable using MRI. Eight T2DM patients were individually matched by age, sex, and race to non-T2DM individuals with similar body mass index (obese) and lean subjects. Functional MRI was performed using a dual-gradient-recalled echo, echo-planar imaging sequence with a repetition time of 1 s and at two echo times (TE = 6 and 46 ms). Data were acquired before, during, and after 10-s isometric dorsiflexion contractions performed at 50 and 100% of maximal voluntary contraction (MVC) force. MRI signal intensity (SI) changes from the tibialis anterior and extensor digitorum longus muscles were plotted as functions of time for each TE. From each time course, the difference between the minimum and the maximum postcontraction SI (ΔSI) were determined for TE = 6 ms (ΔSI(6)) and TE = 46 ms (ΔSI(46)), reflecting variations in blood volume and oxyhemoglobin saturation, respectively. Following 50% MVC contractions, the mean postcontraction ΔSI(6) values were similar in the three groups. Following MVC only, and in the EDL muscle only, T2DM and obese participants had ∼56% lower ΔSI(6) than the lean individuals. Also following MVC only, the ΔSI(46) response in the EDL was lower in T2DM subjects than in lean individuals. These data suggest that skeletal muscle small vessel impairment occurs in T2DM and body mass index-matched subjects, in muscle-specific and contraction intensity-dependent manners.

Evaluation of skeletal muscle during calf exercise by 31-phosphorus magnetic resonance spectroscopy in patients on statin medications

Muscle pain is a common side effect of statin medications, but the cause is poorly understood. We characterized phosphocreatine (PCr) exercise recovery kinetics in 10 patients with hypercholesterolemia before and after a 4-week regimen of statin therapy using 31-phosphorus magnetic resonance spectroscopy ((31) P-MRS). (31) P spectra were obtained before, during, and after exercise on a calf flexion pedal ergometer. Creatine kinase (CK) serum levels were drawn before and after statin therapy. The mean metabolic recovery time constant in subjects increased from 28.1 s (SE = 6.5 s) to 55.4 s (SE = 7.4 s) after statin therapy. The unweighted mean of the pre/post-recovery time difference was -27.3 s (SE = 12.4 s; P = 0.02). Pre- and post-therapy CK levels were not significantly different (P = 0.50). Metabolic recovery time in the calf is prolonged in patients after statin use. This suggests that statins impair mitochondrial oxidative function, and (31) P MRS is a potential study model for statin-associated myopathy.

[Reconsidering fatigue at the onset of multiple sclerosis]

Fatigue is a frequent symptom of multiple sclerosis (MS). It has been reported to varying degrees at all stages of the disease by 50 to 90% of all MS patients. Fatigue is now recognised as a disabling symptom which negatively impacts daily living. This symptom was underrated until recently but has now been included in clinical practice. Most fatigue scales have been developed in the English language and are culturally specific to their country of origin. The Fatigue Severity Scale is a one-dimensional nine-item scale which briefly assesses the impact of fatigue on the daily lives of MS patients. It has been widely used in different studies, even though it appears to be less relevant than the multi-dimensional 40-item Fatigue Impact Scale which was developed in Canada by Fisk et al (1994). The Fatigue Impact Scale is useful because it assesses different aspects of MS-related fatigue, such as the effects of fatigue on cognitive and physical activities and can include daily living. The Multiple Sclerosis Council for Clinical Practice Guidelines recommends the use of a 21-item Modified Fatigue Impact Scale which is a shortened version of the 40-item Fatigue Impact Scale. Using word-for-word translations of these scales into French would fail because the results would not be interpretable. We first translated and culturally adapted the Fatigue Impact Scale to French-speaking patients. We then evaluated the psychometric properties of this French version (EMIF-SEP). We used the EMIF-SEP scale to study fatigue in French MS patients. We found a significant correlation between higher EMIF-SEP total scores and higher EDSS scores; likewise physical dimension of the EMIF-SEP were linked to disability. But no correlations were found between the cognitive aspects of fatigue and disability. Other studies have failed to show any correlation between fatigue and disability. We suggest that this may be due to differences in sample size, or to the type of instrument used to quantify fatigue. As seen above, some tools do not allow for multi-dimensional assessment of fatigue. The EMIF-SEP scale is useful in that it allows for qualitative and quantitative assessment of fatigue.

Repeatability of a dual gradient-recalled echo MRI method for monitoring post-isometric contraction blood volume and oxygenation changes

The purpose of this study was to assess the repeatability of a dual gradient-recalled echo (GRE) muscle functional MRI technique. On 2 days, subjects (n = 8) performed 10 s isometric dorsiflexion contractions under conditions of: (1) maximal voluntary contraction (MVC), (2) 50% MVC (50% MVC), or (3) 50% MVC with concurrent proximal arterial cuff occlusion (50% MVC(cuff)). Functional MRI data were acquired using single-slice dual GRE (TR/TE = 1000/6, 46 ms)-echo planar imaging for 20 s before, during, and for 180 s after each contraction. The mean signal intensity (SI) time courses at each TE (SI(6) and SI(46), reflecting variations in blood volume and %HbO(2), respectively) from the tibialis anterior (TA) and extensor digitorum longus (EDL) muscles were characterized with the post-contraction change in SI and the time-to-peak SI (DeltaSI and TTP, respectively). DeltaSI(6) following an MVC was 36% higher than that obtained after a 50% MVC (p = 0.048). For DeltaSI(6), the highest intraclass correlation coefficients (ICCs) were observed for the TA muscle in the 50% MVC and MVC conditions, with values of 0.83 (p = 0.01) and 0.88 (p = 0.005), respectively. Bland-Altman plots revealed repeatability coefficients (RCs) for the 50% MVC and MVC conditions in the TA muscle of 1.9 and 1.4, respectively. The most repeatable measures for DeltaSI(46) were obtained for the 50% MVC and MVC conditions in the EDL muscle (p = 0.01 and p = 0.04, respectively). Bland-Altman plots revealed RC's for 50% MVC and MVC conditions in the EDL muscle of 3.9 and 5.7, respectively. DeltaSI(6) and DeltaSI(46) increased as a function of the contraction intensity. The repeatability of the method depends on the muscle and contraction condition being evaluated, and in general, is higher following an MVC.

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.

Short-term high-intensity interval training improves phosphocreatine recovery kinetics following moderate-intensity exercise in humans

Previous studies have shown that high-intensity training improves biochemical markers of oxidative potential in skeletal muscle within a 2-week period. The purpose of this study was to examine the effect of short-term high-intensity interval training on the time constant (τ) of phosphocreatine (PCr) recovery following moderate-intensity exercise, an in vivo measure of functional oxidative capacity. Seven healthy active subjects (age, 21 ± 4 years; body mass, 69 ± 11 kg) performed 6 sessions of 4–6 maximal-effort 30 s cycling intervals within a 2-week period, and 7 subjects (age, 24 ± 5 years; body mass, 80 ± 15 kg) served as controls. Prior to and following training, phosphorous-31 magnetic resonance spectroscopy (31P-MRS; GE 3T Excite System) was used to measure relative changes in high-energy phosphates and intracellular pH of the quadriceps muscles during gated dynamic leg-extension exercise (3 cycles of 90 s exercise and 5 min of rest). A monoexponential model was used to estimate the τ of PCr recovery. The τ of PCr recovery after leg-extension exercise was reduced by 14% with high-intensity interval training (pretraining, 43 ± 14 s vs. post-training, 37 ± 15 s; p < 0.05) with no change in the control group (44 ± 12 s vs. 43 ± 12 s, respectively; p > 0.05). These findings demonstrate that short-term high-intensity interval training is an effective means of increasing functional oxidative capacity in skeletal muscle.

Possible mechanisms of the formation of chronic fatigue syndrome in the clinical picture of multiple sclerosis

A frequent manifestation of multiple sclerosis (MS) is chronic fatigue syndrome, which can be defined as a subjective decrease in the level of physical and/or mental energy. Chronic fatigue syndrome can be divided into asthenia (fatigue at rest), pathological fatigability (fatigue on physical loading), and fatigue on the background of deterioration of other symptoms (exacerbation of MS). There are both central and peripheral mechanisms for the formation of fatigue. The combination of fatigue and affective disturbances, especially depression and sleep disorders (insomnia, restless legs syndrome) is common in MS and may provide evidence that they share common mechanisms--decreases in the activity of the serotoninergic and noradrenergic systems. An important component in the formation of chronic fatigue syndrome consists of endocrine and autoimmune factors, the latter having a greater effect on asthenia than on pathological fatigue. Further studies of the pathogenetic mechanisms of the formation of asthenia and pathological fatigue and clarification of their differential diagnostic signs should allow not only a better understanding of the nature of this syndrome, but also better selection of individual treatment.

Physical training and multiple sclerosis

For many years, patients with multiple sclerosis (MS) were advised to avoid exercise because of the risk of increased neurological impairment. This article reviews the literature related to MS and physical exercise. Physical exercise depends on patients' physiological tolerance and response to exercise. MS patients can exhibit dysfunction of cardiovascular adjustment accompanied by respiratory involvement, which can alter aerobic capacity. These abnormalities tend to increase with the neurological impairment. Muscle weakness is the consequence of not only altered central motor drive but also disuse. Several studies have shown the benefits of physical training, with improvements in aerobic capacity, gait parameters and fatigue, and an influence on quality of life. Regular aerobic physical activity is necessary to maintain the benefit of physical training.

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.