Poor Strength,Function, and Low Muscle Density Linked To Hospitalization In The Elderly

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Weak muscle strength (grip and knee extension), poor function (walking speed, chair stands), and low muscle density, but not muscle size or lean mass, are associated with greater risk for hospitalization in elderly adults, according to the results of a prospective cohort study reported online in the July 29 issue of the Journal of the American Geriatrics Society.

"Our research suggests that we need to re-think the way we define sarcopenia or age-related muscle loss," lead author Peggy M. Cawthon, PhD, MPH, from the Research Institute, California Pacific Medical Center in San Francisco, said in a news release. "Many definitions of sarcopenia today tend to focus on lean mass or muscle size, our study shows that is looking at the wrong factors. We found that muscle strength or performance were much better ways of measuring function."

Sarcopenia affects 1 in 5 people older than 65 years in the United States. Estimated direct healthcare costs of treating sarcopenia were more than $18.5 billion in 2000, and these costs should continue to grow with the graying of the US population.

The goal of this study was to evaluate the association between strength, function, lean mass, muscle density, and the risk for hospitalization. At 2 US clinical centers, 3011 adults aged 70 to 80 years who were enrolled in the Health, Aging and Body Composition study underwent measurements of grip and knee extension strength, lean mass, walking speed, and chair stand pace. As a proxy marker for muscle fat infiltration, muscle area and density were determined by computed tomography scans of the thigh.

Local review of medical records determined hospitalizations, and negative binomial regression models separately estimated incident rate ratios (IRRs) of hospitalization for race-specific and sex-specific quartiles of each muscle and function measurement. Age, body mass index, health status, and comorbid conditions were adjusted for using multivariate models. Average duration of follow-up was 4.7 years.

During follow-up, at least 1 hospitalization occurred in 1,678 participants (55.7%). Compared with participants in the highest quartile of muscle density, those in the lowest quartile were more likely to be hospitalized subsequently (multivariate IRR, 1.47; 95% confidence interval [CI], 1.24 - 1.73). The risk for hospitalization was also greater for participants with the weakest grip strength (multivariate IRR, 1.52; 95% CI, 1.30 - 1.78) for the first vs the fourth quartile. Analysis of knee strength, walking pace, and chair stands pace yielded similar results. In contrast, lean mass and muscle area were not associated with the risk for hospitalization.

"The findings are particularly important because they suggest that interventions, such as physical exercise, that improve physical function could help keep more vulnerable seniors out of the hospital," Dr. Cawthon said. "That would not only reduce disability but it would also reduce the huge economic burden associated with hospitalization of the elderly."

Limitations of this study include low generalizability to nonambulatory or infirm elderly, selection bias, inability to determine the temporal association between poor performance and risk for hospitalization, and possible unmeasured confounders.

"Most methods of measuring muscle mass or density rely on complex imaging procedures, such as using quantitative computed tomography (QCT). Those are time consuming and expensive," Dr. Cawthon concluded. "However, we found that much simpler methods — such as measuring walking speed — are much easier and cheaper to do, and are even more accurate in determining a person's risk of future hospitalization. This gives us the ability to screen larger groups of people and help those at risk with some simple interventions, such as physical exercise."


Submitted by DMorgan on Fri, 09/18/2009 - 9:45pm.