It is well known that individual differences exist in exercise capacity or trainability. Several studies have shown that these individual differences are brought about by environmental effects such as life-style, diet and genetics. The potential of several specific genes to cause individual differences in endurance capacity or trainability has been investigated. The angiotensin-converting enzyme (ACE) gene, which has insertion (I) /deletion (D) polymorphism, is one of the most studied genes. Montgomery et al. reported that elite high-altitude mountaineers had higher I allele frequency of the ACE gene than did sedentary males. Moreover, they reported that subjects with II homozygotes showed higher trainability during a 10-week endurance training program than did individuals with ID heterozygotes or DD homozygotes. However, the results reported by Rankinen et al. did not support their results in terms of the relation between ACE genotype and cardiorespiratory endurance. Although numerous studies have reported a relationship between these two items, it remains controversial. Furthermore, mitochondrial DNA (mtDNA), the creative kinase and the Na⁺-K⁺-ATPase ∂2 genes have been studied as genes that may dictate individual differences in endurance capacity or trainability. We are going to report about the relation between these genes and exercise capacity and trainability.

The ability to walk is just as important for the elderly as it is for young people. In fact, in the elderly, decreased mobility limits function in daily life and can lead to more serious situations (e.g., becoming bedridden) . The elderly population has increased over the last decade, and many researchers have studied the mobility of the elderly. However, the focus of most studies has been to facilitate recovery of bedridden individuals and prevent the elderly from becoming bedridden, and particularly to prevent fall-induced fractures, which often cause the elderly to become bedridden. However, about 70-80% of the elderly population do not require care, and it is necessary to conduct research on the maintenance of activities of daily living to make it possible for the elderly to work or volunteer. From this perspective, mobility is an important physical factor. Mobility is dependent on muscle activity and it has long been known that aging reduces muscle mass. Therefore, it is feasible to assume that reduced muscle mass leads to decreased ability to walk, and we have proven that there is a close correlation between the two. When presenting the idea of strength training to the elderly, it is appropriate to focus on the maintenance and improvement of mobility, not on the training itself. The results of our research can be summarized as follows:
Muscle mass decreases with age, with the legs being affected to a greater degree than the arms. Moreover, muscle atrophy is dependent on weakening of muscle fibers, especially fast-twitch (Type II) fibers. Reduced lower limb muscle mass increases the risk of falling and can decrease walking ability to a degree that can affect daily living activities.
In order to improve reduced muscle mass in aging, it is important to use an exercise program that is designed to strengthen fast-twitch fibers, which can be followed even by the elderly. Since walking therapy mostly mobilizes slow twitch fibers, it is not effective in preventing and improving muscle atrophy. It is important to have an exercise program that is designed to mobilize fast-twitch fibers.

Physical fitness including muscle strength and endurance capacity varies substantially among individuals. Physical activity level and exercise behavior also vary among individuals. Many family studies and studies on twins have reported that genetic factors are responsible for heterogeneity in fitness-related traits. However, there is much dispersion in heritability, as previously reported. A systematic review was performed to determine the extent of heritability in physical fitness. A literature search was conducted through PubMed using the following keywords: (heredity or heritability) and (“muscle strength” or “muscle contraction” or endurance or athlete* or fitness or exercise) and (twin* or family). Finally, 43 articles that included 137 phenotypes met the criteria. Only one article focused on the heritability of athletic status. With respect to muscle strength, 23 articles and 54 phenotypes were collected, and showed a range of heritability of 0%-98% (mean: 55±22%). This heterogeneity was partly explained by the ages of subjects. With respect to endurance capacity, 13 articles and 28 phenotypes showed heritability of 0%-93% (mean: 54±25%). The considerable degree of variability in heritability of fitness-related traits may depend on age, sex, race, and environmental factors. Therefore it is necessary to investigate the interaction between genetic factor and factors other than genetic factor. On the other hand, with respect to exercise behavior or physical activity level which is important for improving the physical fitness or health status, the heritability of 0%-85% has also been reported. That is, the genetic factor plays a role in not only physiological phenotypes but also behavioral phenotypes. Understanding of these genetic factors and their mechanisms will lead to improvement in physical fitness or encouragement of physical activity/exercise behavior.

The effects of endurance training and detraining on cardiac autonomic nervous system activity were studied by using the power spectral analysis of heart rate (HR) variability. Twenty-one sedentary male subjects were trained for 8 weeks using cycle ergometer exercise [70% of maximal oxygen uptake (VO₂max), 60 min, 3.4 times/wk] . Resting HR for 5 min was recorded before the training, after the 8-week training period, and after the 2-week and 4-week detraining period. The indices of cardiac parasympathetic and sympathetic nervous system activity were determined by Mem-Calc method, as the high frequency power (HF : 0.15-0.50 Hz) and the ratio of the low frequency power (LF : 0.04-0.15 Hz) to the HF (LF/HF), respectively. The VO₂max after the training and 4 weeks detraining period were significantly higher than the initial value (before training : 41 ± 1 ml/kg/min ; after training: 48±2, P<0.0001; after detraining: 46±2, P<0.001) . The HF was significantly in-creased by the training (P<0.05), and maintained the increased level for the 2-week detraining period (before training : 6.4±0.3 In ms²; after training: 7.0±0.2, P<0.01; after 2-week detrain-ing: 7.0±0.2, P<0.05) . The increase in the HF, however, disappeared after the 4-week detraining period (6.8±0.31n ms²) . The LF/HF did not show any significant changes during the training and detraining period. These results suggest that an endurance exercise with moderate intensity enhan-ces cardiac parasympathetic nervous system activity, but not cardiac sympathetic nervous system activity. The enhanced cardiac parasympathetic nervous system activity, however, may regress rapidly during detraining period.

A physical activity reference value for health promotion, 23 METs-h/week was established by the Ministry of Health, Welfare, and Labour in Japan in 2006. The purpose of this study was to determine the daily step counts (steps/day) that classify adults as meeting the 23 METs-h/week reference value by using objective measurements. Objectively measured physical activity levels of 1837 Japanese adults aged from 23 - 69 yrs from both urban and rural Japanese cohorts were provided. Amount of physical activity and daily step counts were assessed using a triaxial accelerometer (Actimarker EW4800; Panasonic Electric Works). Receiver operating characteristics (ROC) curve analysis determined the optimal daily step counts (steps/day) that discriminated adults who met the reference value from those who did not. Approximately 48 % of Japanese adults met the 23 METs-h/week of physical activity reference value. ROC curve analysis found that 9341 steps/day produced 77.1 % of sensitivity and 79.5 % of specificity in all subject. When the analysis was performed in each cohort, 9980 steps/day and 8640 steps/day were indicated as the optimal daily step counts for them to meet 23 METs-h/week in urban and rural cohort, respectively. These data suggest that Japanese adults are likely to meet 23 METs-h/week of physical activity reference value if they accumulate between 8500 and 10,000 steps/day of daily step counts.

High-sensitivity C-reactive protein (CRP) is a novel risk factor for coronary artery disease. It is well known that body weight loss is effective in reducing serum CRP concentration ; however, the effect of exercise training on serum CRP concentration has not been fully elucidated. The purpose of this study was to examine the effect of a 24-week exercise training program on serum CRP concentration in 169 healthy middle-aged and elderly subjects (65.9±6.4 years). Each subject underwent baseline testing (peak oxygen uptake, daily physical activity, body weight, and serum CRP levels), and repeated these tests on completion of the training program. The subjects were classified into 2 groups based on initial CRP levels : normal<1.0 mg/L, n=139, and high≥1.0mg/L, n=30. On completion of the program, both daily physical activity and peak oxygen uptake increased significantly (+33.9±72.4%, p<0.0001, +5.4±14.7%, p=0.014, respectively). However, body weight did not change significantly. In addition, CRP levels of the entire group did not change significantly. However, CRP levels significantly decreased among the high baseline CRP group (from 1.82±0.81 mg/L to 0.98±0.59 mg/L, p<0.0001). It was concluded that serum CRP levels are reduced without body weight loss in response to exercise training in healthy middle-aged and elderly subjects with high initial CRP levels.

The purpose of this study was to develop prediction models of sarcopenia in 1,894 Japanese men and women aged 18-85 years. Reference values for sarcopenia (skeletal muscle index, SMI; appendicular muscle mass/height², kg/m²) in each sex were defined as values two standard deviations (2SD) below the gender-specific means of this study reference data for young adults aged 18-40 years. Reference values for predisposition to sarcopenia (PSa) in each gender were also defined as values one standard deviations (1SD) below. The subjects aged 41 years or older were randomly separated into 2 groups, a model development group and a validation group. Appendicular muscle mass was measured by DXA. The reference values of sarcopenia were 6.87 kg/m² and 5.46 kg/m², and those of PSa were 7.77 kg/m² and 6.12 kg/m². The subjects with sarcopenia and PSa aged 41 years or older were 1.7% and 28.8% in men and 2.7% and 20.7% in women. The whole body bone mineral density of PSa was significantly lower than in normal subjects. The handgrip strength of PSa was significantly lower than in normal subjects. Stepwise regression analysis indicated that the body mass index (BMI), waist circumference and age were independently associated with SMI in men; and BMI, handgrip strength and waist circumference were independently associated with SMI in women. The SMI prediction equations were applied to the validation group, and strong correlations were also observed between the DXA-measured and predicted SMI in men and women. This study proposed the reference values of sarcopenia in Japanese men and women. The prediction models of SMI using anthropometric measurement are valid for alternative DXA-measured SMI in Japanese adults.

This study aimed to develop affective experience, attitude, and behavioral intention scales for exercise, and examine their associations with exercise behavior. A web-based questionnaire survey was conducted among 500 individuals aged 60 to 69 years at baseline. The survey measured respondents’ affective experiences, attitude, behavioral intention, exercise behavior, and demographic factors. The same survey was conducted 2 weeks (n = 345) and 1 year later (n = 338). Exploratory and confirmatory factor analyses showed that the factor structures of the affective experience (2 factors: 3 items each for positive experience and negative experience), attitude (2 factors: 3 items each for affective attitudes and instrumental attitudes), and behavioral intention scales (2 factors: 4 items each for intention to maintain behavior and intention to overcome barriers) were acceptable. For these scales, the Cronbach’s alpha coefficients ranged from 0.69 to 0.92, Pearson’s correlation coefficients for baseline and 2-week follow-up ranged from 0.51 to 0.81, and Cohen’s d values for the associations with exercise behavior ranged from 0.46 to 0.98. After adjusting for demographic factors and exercise behavior at baseline, structural equation modeling showed that an affective attitude toward exercise at baseline significantly predicted exercise behavior at 1-year follow-up (standardized coefficient = 0.27), and that the affective attitude was predominantly explained by the positive affective experience of exercise (standardized coefficient = 0.80). The results confirmed the validities and reliabilities of the scales. Positive affective experiences and affective attitudes may be important determinants of exercise behavior.

The purpose of this study was to develop prediction models of sarcopenia in 1,894 Japanese men and women aged 18-85 years. Reference values for sarcopenia (skeletal muscle index, SMI; appendicular muscle mass/height2, kg/m2) in each sex were defined as values two standard deviations (2SD) below the gender-specific means of this study reference data for young adults aged 18-40 years. Reference values for predisposition to sarcopenia (PSa) in each gender were also defined as values one standard deviations (1SD) below. The subjects aged 41 years or older were randomly separated into 2 groups, a model development group and a validation group. Appendicular muscle mass was measured by DXA. The reference values of sarcopenia were 6.87 kg/m2 and 5.46 kg/m2, and those of PSa were 7.77 kg/m2 and 6.12 kg/m2. The subjects with sarcopenia and PSa aged 41 years or older were 1.7% and 28.8% in men and 2.7% and 20.7% in women. The whole body bone mineral density of PSa was significantly lower than in normal subjects. The handgrip strength of PSa was significantly lower than in normal subjects. Stepwise regression analysis indicated that the body mass index (BMI), waist circumference and age were independently associated with SMI in men; and BMI, handgrip strength and waist circumference were independently associated with SMI in women. The SMI prediction equations were applied to the validation group, and strong correlations were also observed between the DXA-measured and predicted SMI in men and women. This study proposed the reference values of sarcopenia in Japanese men and women. The prediction models of SMI using anthropometric measurement are valid for alternative DXA-measured SMI in Japanese adults.