Arthritis & Rheumatism, Volume 63,
November 2011 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Chicago, Illinois November 4-9, 2011.


Muscle Area and Muscle Quality Relate to Physical Activity in Subjects with Rheumatoid Arthritis.

Khoja,  Samannaaz S., Almeida,  Gustavo JM, Goodpaster,  Bret H., Piva,  Sara R.

Background/Purpose:

People with Rheumatoid Arthritis (RA) experience a reduction in lean muscle mass and an increase in fat mass due to metabolic abnormalities caused by the disease. Low lean muscle mass associates with decreased muscle strength and physical function, and may play a role in the low levels of physical activity (PA) reported in this population. To our knowledge, direct associations between lean muscle mass and PA have not been established in RA. Investigating this relationship may help optimize strategies to improve PA participation. In addition to muscle mass, muscle quality may also affect PA. Muscle quality may be characterized by its muscle attenuation (MA) coefficient and provides information about amount of fatty tissue present within the muscle. Studies in other populations suggest that increased intramuscular fat affects overall muscle function. The aim of this study was to investigate the association of thigh muscle area and muscle quality and PA in subjects with RA

Methods:

Cross-sectional study on 17 subjects with RA (age 61.5± 10.6 yrs; RA duration 17.2 ± 3 yrs; BMI 30.6 ± 7.6 kg/m2; 13 female). PA was measured at several low intensity levels by the Sense Wear armband, a multi-sensor portable activity monitor that provides data on energy expenditure (EE) of PA performed above 1 metabolic equivalent level (PAEE>=1MET), EE of PA performed above 2METs (PAEE>=2METs), and EE of PA performed above 3METs (PAEE>=3METs). Mid-thigh cross-sectional area (CSA) of each leg was measured by computed tomography (CT), and averaged for both sides. The mean MA of the mid-thigh CSA was calculated for each leg using the Slice-O-matic software, and averaged for both sides. MA coefficient ranges from 0 to 100 Hounsfield units (HU), higher numbers indicate lower intramuscular fat and better muscle quality. We calculated the correlations between mid-thigh CSA and MA with PAEE above 1, 2 and 3 METs. We accounted for body size in the analysis by controlling for BMI.

Results:

Total mid-thigh CSA and mean MA both showed positive associations of moderate strength with PAEE>=1MET, PAEE>=2METs and PAEE>=3METs after controlling for BMI. Results suggest that subjects with higher area of thigh muscle and lower amount of intramuscular fat have higher levels of PA. Variable descriptives and semi-partial correlation coefficients are depicted in the Table.

Table. Associations between Muscle Cross-sectional Area (CSA) and Mean Muscle Attenuation (MA) Coefficients with Physical Activity Energy Expenditure (PAEE)

  Semi-Partial Correlation Coefficients After controlling BMI
VariablesMedians (IQ:25–75)PAEE>=1METPAEE>=2METsPAEE>=3METs
Mid-Thigh CSA (sq cm)94.2 (84.2–111.3)0.64*0.59*0.65*
Mid-Thigh mean MA (HU)41.7 (38.9–44.5)0.440.45*0.52*
PAEE>=1MET (kcal/min)913.0 (449.0–1212.5)   
PAEE>=2METs (kcal/min)488 (165.5–773.5)   
PAEE>=3METs (kcal/min)128.0 (29.0–332.0)   
* significant at a–level of 0.05.

Conclusion:

The findings suggest that perhaps improving muscle mass and muscle quality may lead to an increase in PA participation in patients with RA. An increased participation in physical activities reduces cardiovascular risk, which is an important predictor of morbidity and mortality in RA. In order to optimize interventions to promote PA participation, future longitudinal trials should consider the effects of muscle mass and quality while investigating changes in PA.

To cite this abstract, please use the following information:
Khoja, Samannaaz S., Almeida, Gustavo JM, Goodpaster, Bret H., Piva, Sara R.; Muscle Area and Muscle Quality Relate to Physical Activity in Subjects with Rheumatoid Arthritis. [abstract]. Arthritis Rheum 2011;63 Suppl 10 :1560
DOI:

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