Effect of physical training on the proportion of slow-twitch type I muscle fibers, a novel nonimmune-mediated mechanism for muscle impairment in polymyositis or dermatomyositis

Exploratory analysis of the relationships between aerobic capacity and self-reported fatigue in patients with rheumatoid arthritis, polymyositis, and chronic fatigue syndrome

OBJECTIVE

To determine if self-reported levels of physical activity and fatigue are related to peak oxygen uptake (VO(2peak)) and whether these relationships differ among the patient groups (rheumatoid arthritis [RA], polymyositis [PM], and chronic fatigue syndrome [CFS]).

DESIGN

Correlational investigation.

SETTING

Two ambulatory research clinics at the National Institutes of Health, Clinical Center, Bethesda, MD.

PARTICIPANTS

There were 9 patients with PM, 10 with RA, and 10 with CFS. All patients met case criteria for their respective diagnoses. METHODS/MAIN OUTCOME MEASUREMENTS: VO(2peak) during bicycle ergometry and self-reported fatigability, fatigue, and physical activity. VO(2peak) was used as the criterion measurement of physiological fatigue with which the self-reported variables were compared.

RESULTS

The Pearson r revealed that self-reported physical activity correlated with VO(2peak) (r = 61, P = .01). However, fatigability and fatigue did not correlate with VO(2peak). Linear regression analysis was performed to assess the effects of diagnosis group, self-reported activity level or fatigue, and their interaction. A trend in the data showed a distinctive relationship between fatigue/fatigability within the 3 groups. In addition, when controlling for group status, self-reported activity predicted aerobic capacity as measured by VO(2peak).

CONCLUSIONS

This study confirms that patients with chronic, but stable RA, PM, or CFS are fatigued and have significantly decreased aerobic capacity. Self-reports of physical activity predicted VO(2peak), and may be used as an indicator of activity-based aerobic capacity. Self-reports of fatigue, however, did not correlate with VO(2peak) and hence are assessing something other than an index of aerobic capacity, and provide additional information about patients' perceptions, which will require further investigation.

Improvement in aerobic capacity after an exercise program in sporadic inclusion body myositis

OBJECTIVES

The study aimed to investigate the effects of a combined functional and aerobic exercise program on aerobic capacity, muscle strength, and functional mobility in a group of patients with sporadic inclusion body myositis (IBM).

METHODS

Aerobic capacity, muscle strength, and functional capacity assessments were conducted on 7 participants with sporadic IBM before and after a 12-week exercise program, which included resistance exercises and aerobic stationary cycling 3 times per week on alternative days.

RESULTS

Aerobic capacity of the group increased significantly by 38%, and significant strength improvements were observed in 4 of the muscle groups tested (P < 0.05). The exercise program was well tolerated, and there was no significant change in the serum creatine kinase level after the exercise period.

CONCLUSIONS

An aerobic exercise program can be safely tolerated by patients with sporadic IBM and can improve aerobic capacity and muscle strength when combined with resistance training. These findings indicate that aerobic and functional muscle strengthening exercise should be considered in the management of patients with IBM.

Exercise effects in patients with adult idiopathic inflammatory myopathies

PURPOSE OF REVIEW

To give an update on recent findings on effects of exercise in patients with adult inflammatory myopathies.

RECENT FINDINGS

Although responding to treatment, a majority of patients with polymyositis and dermatomyositis develop sustained disability. The reason for this is not clear. However, a recent study further supports the hypothesis of hypoxia in muscle tissue as a contributor to muscle weakness. The percentage of type I oxygen-dependent muscle fibers increased after a 12-week submaximal home exercise program along with improved muscle endurance in patients with chronic polymyositis or dermatomyositis. Creatine supplements in addition to the same home exercise program are more beneficial than exercise alone in patients with chronic polymyositis or dermatomyositis. Patients with chronic disease tolerate intensive resistance training resulting in improved muscle strength and muscle endurance. This 7-week exercise study also reported reduced disease activity and possibly even reduced muscle inflammation.

SUMMARY

These recent studies are in line with earlier ones further supporting safety and efficacy of exercise in patients with polymyositis or dermatomyositis. There is an urgent need for larger randomized controlled trials also including patients with inclusion body myositis to further increase knowledge of disease mechanisms causing disability, exercise effects, and what exercise program is most efficient in patients with different entities of idiopathic inflammatory myopathies.

Upregulation of MHC class I in transgenic mice results in reduced force-generating capacity in slow-twitch muscle

Expression of major histocompatibility complex (MHC) class I in skeletal muscle fibers is an early and consistent finding in inflammatory myopathies. To test if MHC class I has a primary role in muscle impairment, we used transgenic mice with inducible overexpression of MHC class I in their skeletal muscle cells. Contractile function was studied in isolated extensor digitorum longus (EDL, fast-twitch) and soleus (slow-twitch) muscles. We found that EDL was smaller, whereas soleus muscle was slightly larger. Both muscles generated less absolute force in myopathic compared with control mice; however, when force was expressed per cross-sectional area, only soleus muscle generated less force. Inflammation was markedly increased, but no changes were found in the activities of key mitochondrial and glycogenolytic enzymes in myopathic mice. The induction of MHC class I results in muscle atrophy and an intrinsic decrease in force-generation capacity. These observations may have important implications for our understanding of the pathophysiological processes of muscle weakness seen in inflammatory myopathies. Muscle Nerve, 2008.

Developments in the scientific and clinical understanding of inflammatory myopathies

The idiopathic inflammatory myopathies are chronic autoimmune disorders sharing the clinical symptom of muscle weakness and, in typical cases, inflammatory cell infiltrates in muscle tissue. During the last decade, novel information has accumulated supporting a role of both the innate and adaptive immune systems in myositis and suggesting that different molecular pathways predominate in different subsets of myositis. The type I interferon activity is one such novel pathway identified in some subsets of myositis. Furthermore, nonimmunological pathways have been identified, suggesting that factors other than direct T cell-mediated muscle fibre necrosis could have a role in the development of muscle weakness.

[Current treatments of dermatomyositis and polymyositis]

Idiopathic inflammatory myositides are chronic diseases affecting predominantly the musculoskeletal system and involving high morbidity and mortality. Even when treated with glucocorticosteroids, patients often experience a progressive or relapsing course of the disease, requiring additional immunosuppressants, biologicals, or other therapeutic interventions. Randomized controlled trials on the treatment of primary myositides are still lacking, which means that the optimum therapeutic regimen has still not been defined. This article reviews the current position indicated by the data collected in standard and modern therapeutic options for the treatment of idiopathic inflammatory myositides.