Association of vigorous physical activity with age-related, site-specific loss of thigh muscle in women: the HIREGASAKI study

Abstract

body, constitutes approximately 40% of fat-free body mass in young adults1 but decreases with advancing age, especially after the fifth decade of life.2 These age-related changes lead to a decline of strength and power, a decrease in physical performance, and disability.3 Because the population of elderly people is growing in most countries, including Japan, the agerelated loss of skeletal muscle mass is likely to have a severe economic impact on the healthcare system. Age-related loss of skeletal muscle mass (Sarcopenia) has been studied extensively by evaluating muscle volume, muscle cross-sectional area (CSA), and anatomical muscle thickness (MTH).4 Recently, Abe and colleagues demonstrated that age is associated with site-specific loss of skeletal muscle mass in Japanese men and women5,6 and in German men7. Interestingly, in the anterior and posterior regions of the thigh, age-related muscle loss was observed in the quadriceps but not in the hamstrings and adductors.8 The etiology of sitespecific sarcopenia is multifactorial and complex. Several factors have been implicated such as declining anabolic hormone concentrations, nutritional deficiencies, chronic inflammation, and insulin resistance.5,7 Decreased physical activity levels that occur with aging also contribute to sarcopenia. It is well established that hormonal receptors for mRNA and transcriptional activity are increased8 and that there is reduced insulin resistance9 in exercising muscles following an acute bout of exercise for sedentary individuals. There are therefore many important interrelationships between physical activity levels and other etiologic factors associated with health and aging that may contribute in varying degrees to the age-related loss of skeletal muscle mass in older populations. More recently, we examined the effect of habitual physical activity on age-related loss of skeletal muscle and found that there is site-specific loss in both active (more than once a week) and inactive old women.10 In that study, the subjects were classified into active and inactive groups based on their self-reported habitual physical activity. The effect of exercise intensity and duration of daily physical activities on site-specific loss of thigh muscle is unknown. However, muscle mass and strength losses associated with increasing age