| Jan 12, 2015
By David M. Gundermann, Ph.D, and Todd M. Manini, Ph.D., FACSM
|David M. Gundermann, Ph.D |
|Todd M. Manini, Ph.D., FACSM |
Over the next 20 years, the aging of the population and obesity epidemic will collide. These two aircraft carriers of health burden are expected to lead to the nation’s growing health issues. First, aging is associated with a dramatic and progressive loss of muscle mass and quality, which partly leads to a diminished functional ability, increased susceptibility to disease and a declining physical quality of life leading to the possibility of physical dependence. Individuals who lose significant muscle mass are considered to be sarcopenic and, as a result, they typically have low appendicular lean mass relative to body height. Second, advancing age leads to their increased susceptibility to weight gain that contributes to development of obesity, along with a host of cardiovascular, metabolic and functional consequences. Accordingly, there has been a rising concern that older adults who possess both low amounts of appendicular muscle and high levels of adipose tissue are particularly vulnerable to physical disability and health consequences. Low levels of muscle relative to the total fat mass clearly predisposes to metabolic dysregulation and biomechanical disadvantages in performing tasks of daily life against gravity (e.g., stair climbing, chair rising, etc…)
Sarcopenic obesity (a phrase coined in 2000) is difficult to easily detect because many older adults maintain their body weight, but experience a body composition shift with losses in muscle mass and reciprocal gains in fat mass. Additionally, there are no clear criteria, nor are there well defined cutoffs for sarcopenic obesity. For example, there are at least five different published benchmarks, leading to different prevalence estimates ranging from 4 to 40 percent. More importantly, though, the debate about defining sarcopenic obesity is dwarfed by the debate about the actual health concerns it poses. One could assume that the combination of obesity and low muscle mass would lead to an additive effect on health risks, although that may be an unfair assessment. That is because those labeled with sarcopenic obesity still have significantly more muscle than those with frank sarcopenia (even by all the current definitions). Thus, in fact, they might not be expected to have the same health risks associated with sarcopenia. A more apt comparison tends to be between the obese and the sarcopenic obese. So far, there are mixed results in the research literature that the latter condition predicts higher health and disability risks.
While it is a worthwhile endeavor to compartmentalize the older adult population into risk categories, sarcopenic obesity may simply be the natural progression from obesity, considering that high fatness, in fact, predicts accelerated loss of muscle. Therefore, even though sarcopenic obesity is a relatively new concept that is gaining traction, there remains much to be understood about whether additional risk is conferred by the condition, especially if you consider covariates such as changes in daily activity and diet. Regardless of the causes and consequences, sarcopenic obesity is a condition that can benefit from existing treatments of physical activity and appropriate dietary intake. Viewpoints presented on the ACSM blog reflect opinions of the authors and do not necessarily reflect positions or policies of ACSM.
Drs. David Gundermann and Todd Manini are geriatric exercise scientists in the Department of Aging and Geriatric Research at the University of Florida. Their research focuses on enhancing skeletal muscle for preventing physical disability in late life. Both are members of ACSM and are actively involved with research to treat obesity and sarcopenia. Dr. Manini serves on ACSM’s Strategic Health Initiative on Aging Committee and has received an award from the ACSM’s Paffenbarger-Blair Fund for epidemiological research on physical activity.