Required muscle mass for preventing lifestyle-related diseases in Japanese women.(Research article)

Authors: Masae Miyatani (corresponding author) [1,2]; Hiroshi Kawano [3,4]; Kei Masani [1,2]; Yuko Gando [3,4]; Kenta Yamamoto [4,5]; Michiya Tanimoto [4]; Taewoong Oh [6]; Chiyoko Usui [3,7]; Kiyoshi Sanada [4,5]; Mitsuru Higuchi [7]; Izumi Tabata [4]; Motohiko Miyachi [4]

Background

Previous epidemiologic and clinical evidence indicate that a poor cardiorespiratory fitness is a major risk factor for life-style related diseases (LSRD) such as obesity, hypertension, hypercholesterolaemia, arteriosclerosis and diabetes [1, 2, 3, 4]. Moreover, low cardiorespiratory fitness has been found to be a predictor of cardiovascular disease (CVD) mortality, and all-cause mortality [5, 6, 7, 8]. Thus, it is essential to maintain a high level of cardiorespiratory fitness to prevent LSRD.

Cardiovascular fitness is usually evaluated as the maximal oxygen uptake per body mass (

V o2 max, mL*kg-1 *min-1 ). The Japanese Ministry of Health Labour and Welfare in 2006 proposed V o2 max reference values for each age group to prevent LSRD [9]. These V o2 max reference values were determined by the "Committee for the Determination of the Recommended Exercise Allowance and Exercise Guide" established in August 2005, and were referenced in the "Exercise and Physical Activity Reference Quantity for Health Promotion 2006 (EPAR2006)". Originally, the "Recommended Quantity of Exercise for Health Promotion (1989)" had been formulated to mainly target the prevention of coronary artery disease. With the passage of more than 15 years following the establishment of this standard, the morbidity pattern of people has worsened and LSRD have increased in prevalence. In order to face this situation, the EPAR2006 was made based on the latest scientific evidence, and was designed to maintain and promote the health of people and prevent LSRD by improving their capacity for physical activity and exercise. These V o2 max reference values proposed in the EPAR2006 were determined by experts through the systematic review of literature regarding the relationship between V o2 max and LSRD such as obesity, hypertension, hypercholesterolemia, diabetes, cerebrovascular disease, CVD mortality and all-cause mortality.

It is well known that

V o2 max decreases with age [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]. It has been suggested that the age-related decline in V o2 max is a consequence of attenuation of central and peripheral functions such as stroke volume, heart rate max (HRmax ), peripheral O2 extraction, and lean body mass (LBM) or muscle mass [19, 21, 22, 23, 24, 25]. Among these determinants, reductions in HRmax and LBM or muscle mass have been suggested to be primary factors [26, 27]. While many studies on cardiovascular fitness have focused on cardiac measurements, it should be emphasized that muscle mass is one of the critical determinants of V o2 max [13, 14, 19, 24, 26, 28, 29, 30] since the amount of tissue available to extract oxygen during maximal exercise, i.e., muscle, can directly contribute to the value of V o2 max. For example, Sanada et al. reported the MRI-measured lower body skeletal muscle mass was closely associated to the absolute V o2 max during running [28, 30]. Additionally, the age-related decrement in V o2 max can be related to the age-associated muscle loss [24, 19]. Further, it is important to notice that LBM or muscle mass can be maintained to some degree by exercise training, while such training cannot prevent age-related declines in HRmax , [26, 27].

Therefore, we hypothesized that a certain level of muscle mass required to maintain sufficient cardiovascular fitness is present and that it could be a limiting factor of age-related

V o2 max attenuation. Based on this hypothesis, it is advantageous to Japanese women's health to propose such muscle mass required to maintain sufficient V o2 max. Thus, the purpose of this study was to determine a required value of muscle mass to maintain the V o2 max reference value determined by the Japanese Ministry of Health Labour and Welfare in 2006 (Ministry of Health, Labour and Welfare of Japan 2006).

Methods

Subjects

A group of 403 Japanese women aged 20 to 69 years were randomly allocated to either a validation group (V-group, n = 201) or a cross-validation group (CV-group, n = 202). The subjects were recruited from the community around the National Institute of Health and Nutrition. All subjects were active and free of overt CVD assessed using a medical history questionnaire. All assessments were conducted at the National Institute of Health and Nutrition between February 2004 and October 2006. The study was approved by the Ethics Committee of the National Institute of Health and Nutrition, and written consent was obtained from all participants.

Percentage of muscle mass

The lean soft tissue mass of legs and arms were measured with a whole-body Dual Energy X-ray Absorptiomettry (DXA) scanner (Hologic QDR-4500, Hologic INC., Waltham, MA, USA). The body regions were delineated according to specific anatomical landmarks using manual DXA analysis software (version11.2.3). The appendicular lean soft tissue mass was calculated as a sum of the lean soft tissue mass of the legs and the arms. The lean soft tissue mass of extremities assessed using DXA …