The etiology and exercise implications of sarcopenia in the elderly

An increasing aging population greatly impacts health care services worldwide. A large percentage of healthcare expenditures for seniors arise from the negative outcomes of muscle loss, also known as sarcopenia. Aging-related losses of muscle strength and quality impair balance, walking ability and endurance and cause negative events such as falls, incident disability and frailty. This review systemically explores the significance of sarcopenia in the elderly and addresses several important physiological mechanisms of sarcopenia. The implications of crucial exercise regimens that improve muscle strength and delay the onset of sarcopenia are also discussed. Copyright © 2015, Chinese Nursing Association. Production and hosting by Elsevier (Singapore) Pte Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/). A rapidly expanding aging population is one of the factors that impacts health care services across the globe. According to statistics from the U.S. Bureau of the Census, the number of people who are 65 years or older (seniors) equaled 43.1 million in July 2012, representing 15% of the U.S. population. By 2050, it is projected that there will be about 83.7 million seniors representing almost 20% of the population [1]. Health care expenditures for seniors in the U.S. are expected to increase six-fold by 2040 [2] and a high percentage of health care costs for seniors arise from the negative outcomes of lean muscle mass loss [3]. This review explores the impact of sarcopenia, which refers to the loss of muscle mass and the decline of muscle quality with increased age [4], on the mobility and independence of the elderly. The physiological causes of sarcopenia and the implications of exercise regimens to improve muscle strength or to delay sarcopenia are discussed. Nursing Association. g Association. Production ://creativecommons.org/ 1. Significance of sarcopenia The term of “sarcopenia” was first introduced in 1989 to describe a progressive, generalized loss of skeletal muscle mass and accompanying decline in muscle strength and performance with increasing age. Sarcopenia is associated with many negative outcomes, such as disability, frailty, comorbidities, hospital admissions and death [4e6]. The prevalence of sarcopenia with advanced age has been well-documented. Baumgartner and colleagues [7] utilized data from a population-based study and analyzed the epidemiology of sarcopenia among the New Mexico elderly. The prevalence of sarcopenia was 13e14% in persons under age 70 and >50% in those older than 80. In a 7.8 year longitudinal study, Forbes and Reina [8] reported an average loss of 0.25 kg/ year of lean muscle mass among the participants aged 22e53. and hosting by Elsevier (Singapore) Pte Ltd. This is an open access licenses/by-nc-nd/4.0/). i n t e r n a t i o n a l j o u rn a l o f n u r s i n g s c i e n c e s 2 ( 2 0 1 5 ) 1 9 9e2 0 3 200 The significant consequences of sarcopenia have also been well-recognized. Roubenoff [9] investigated the close relationship between muscle mass and strength and found that sarcopenia was important in functional deterioration, including declines in gait and balance, increased fall risks, and loss of independence [10]. Murphy and colleagues [11] examined the time-course of sarcopenia determinants and found that low functioning, lack of physical activity and a high body mass indexpredicted transition toward sarcopenia,whichwas more likely to lead to death. Szulc and associates [12] assessed the degree of sarcopenia by the relative appendicular skeletal muscle (RASM)mass index. They found that a decreasedRASM value among elderlymenwas associatedwith a lower bending strength. Therefore, the authors concluded that sarcopenia in older men was associated with impaired balance and an increased risk of falling. The relationship between sarcopenia and functional status was also investigated in the NewMexico Study, which revealed that people with sarcopenia had 3e4 fold higher rates of disability, significantly greater risks of falling, andweremore likely to use assistive devices [7]. Metter et al. [13] found that sarcopenia could act as a significant predictor of all-cause mortality. The loss of muscle mass and quality also has metabolic and physiological consequences. Sarcopenia may influence the body's thermoregulation process in both cold and warm environments [14] and may contribute to age-associated glucose intolerance [15]. Therefore, sarcopenia not only has detrimental effects on physical functioning, but also impacts skeletal and metabolic health. Sarcopenia greatly diminishes the overall quality of life [3]. 2. Etiology of sarcopenia Sarcopenia, likemany other problems that occurwith aging, is a multifactorial condition. Factors that contribute to the occurrence of sarcopenia in the elderly include motor units, protein metabolism, hormones and lifestyle [9].