Poor Muscle Strength Predicts Immobility in Obese ElderlyTuesday, July 7, 2009
Students and residents in my clinic are often surprised when I refer to my severely obese patients as olympian athletes – most people I know, who consider themselves fairly athletic, would be unable to even stand up out of their chairs let alone walk 10 steps were they to suddenly weigh 400 lbs or more.
For the same reason I consider Jillian and Bob the biggest losers on the Biggest Loser show, as neither of them would last even 5 minutes doing any of their exercises and drills wearing a 200 lb fat suit (something they regularly expect of their poor contestants).
That said, losing some of that incredible muscle (or lean body mass) in an obese individual is always a reason for grave concern – I have previously referred to it as a medical emergency. We routinely see severely obese patients, who were fully mobile on their own prior to admission, unable to even stand on their own after a few days in a hospital bed. This offloading-atrophy is a major complication and frequent cause of extended immobility in severely obese patients.
That losing lean body mass (for whatever reasons) is never a good sign, not even for obese individuals, who generally have plenty of muscle to go around, is shown in a new study by Sari Stenholm and colleagues from the National Institute on Aging, Baltimore, MD, published in this month’s issue of the International Journal of Obesity.
This study examined whether older obese persons with low muscle strength experience significantly greater declines in walking speed and mobility than comparable persons with only obesity or low muscle strength.
The study population consisted of 930 community-dwelling adults aged 65 years or older living in the Chianti geographic area (Tuscany, Italy) and were followed for 6 years (inChianti study).
Obesity was defined as BMI equal or greater than 30 and low muscle strength as lowest sex-specific tertile of knee extensor strength. Walking speed and self-reported mobility disability (ability to walk 400 m or climb one flight of stairs) were assessed at baseline and at 3- and 6-year follow-up.
As expected, at baseline, obese persons with low muscle strength had lower walking speed compared with all other groups.
More importantly, in the longitudinal analyses, obese participants with low muscle strength at baseline had a much steeper decline in walking speed and substantially higher risk of developing new mobility disability over the 6-year follow-up period.
Interestingly, this difference was seen only before age 80, whereafter the role of muscle strength (or sarcopenia) appeared to diminish (or the sample size was simply no longer large enough to detect an effect).
The study emphasizes the importance of assessing muscle strength (which similar to fitness testing) may serve as an important predictor of immobility and perhaps mortality in obese individuals.
Although this study only examined older individuals, I would not be surprised if similar observations regarding sarcopenia were made in younger obese individuals. As posted before, obesity is a significant risk factor for early disability and it is reasonable to assume that this risk is probably highest for individuals who have poor muscle strength.
Will strength training prevent early immobility and improve outcomes? I would not be surprised if it did.