Purpose: Disability in patients with rheumatoid arthritis (RA) is a multifactorial process involving various unaccounted factors. Loss of lean body mass plays an important role in impaired physical function, and exercise studies in RA have shown promising results in restoring muscle mass, strength, and function. However, no comprehensive assessment of the muscle characteristics has been undertaken to determine whether qualitative changes in muscle also contribute to RA disability. This study explores the physiological muscle properties of a community-based population with stable RA.
Methods: Vastus lateralis (VL) force and physiological cross-sectional area (PCSA), voluntary muscle activation capacity, and contractile properties were assessed in 23 patients with stable RA (age = 60 ± 2 yr (mean ± SEM); 16 women) and age- and sex-matched healthy controls (age = 60 ± 3 yr). Measurements with EMG were obtained during maximal isometric knee extension contractions, with resting and superimposed electrical stimulations. Concentric knee extension contractions were also assessed. Pennation angle and VL volume were measured with ultrasound to determine fiber fascicle length and PCSA. Muscle-specific force was calculated (VL force/VL PCSA). Body composition using dual-energy x-ray absorptiometry and objective physical function were also measured.
Results: The patients displayed typical features of RA with reduced physical function (P = 0.001-0.09), a trend toward lower appendicular lean mass (P = 0.09) and increased total body fat (P < 0.05) relative to controls. However, there were no differences in specific force, contractile properties, voluntary activation capacity, and contraction velocity (P = 0.41-0.99). VL PCSA was reduced (P < 0.05) with minor architectural changes in patients with RA.
Conclusions: Physiological properties of muscle that determine specific force are not compromised in patients with stable RA despite deficits in physical function.
1School of Sport, Health and Exercise Sciences, Bangor University, Wales, UNITED KINGDOM; and 2Department of Rheumatology, Llandudno Hospital, Betsi Cadwaladr University Health Board, UNITED KINGDOM
Address for correspondence: Verena Matschke, M.D., M.R.C.P., School of Sport, Health and Exercise Sciences, Bangor University, George Building, Holyhead Road, Bangor, Gwynedd LL57 2PZ, United Kingdom; E-mail: firstname.lastname@example.org.
Submitted for publication January 2010.
Accepted for publication April 2010.