PURPOSE:Walking is a major exercise for maintaining good health. However, with age joint degeneration progresses and musculoskeletal tolerance to mechanical stress caused by walking decreases. Therefore, to extend the walking life without age-related walking problems, we developed New Ninja-Walk, which was designed in consideration of reducing mechanical stress, and then, examined the effects of its smooth walking. METHODS:The first examination, we measured 10-m walking speed and 3D acceleration using Safety Walk Navi (Descente Ltd, Osaka, Japan) for older adults (n=451, 72.1±5.1years) who could walk on their own, and examined their acceleration distribution ranges, i.e. markers of mechanical stress during a walking test. In the second examination, a 30-minute New Ninja-Walk workshop was held for older adults (n=67) who could walk on their own. Before and after the workshop, the same measurements and stride as the first examination were measured. Since the acceleration changes depending on the walking speed, only the participants whose speed change before and after was 0.2m/sec or less (n=47, 75.2±6.1 years) were compared. RESULTS: In the first examination, there was a positive correlation between walking speed and acceleration (forward acceleration: r=0.61, upward acceleration: r=0.76, downward acceleration: 0.36, and lateral acceleration: r=0.43, all P<0.01). In addition, even if, their accelerations were same at the walking speed, a considerable width distribution area was observed. In the second examination, after introducing the New Ninja-Walk, their, stride narrowed from 0.433±0.043 (height ratio) before the workshop to 0.417±0.038 after the workshop (P<0.01). Acceleration was reduced in three directions except downward (forward: to 0.668±0.219g from 0.789±0.28g, upward: to 0.418±0.1g from 0.4620.116g, lateral: to 0.817±0.216 from 0.936±0.232g, all P<0.01). CONCLUSION: We found that the faster the walking speed, the greater the mechanical stress. However, there was a difference in mechanical stress depending on how they walked. As a result of devising and practicing a smooth walking style like a ninja, mechanical stress was generally reduced.
METHODS: Forty female mice(4 weeks old) were randomly divided into a lifelong exercise(LE), premenopausal exercise(PE), adolescent exercise(AE) and blank control(BC) groups consisting 10 mice in each group. The mice in the LE firstly underwent swimming exercise for 12 consecutive weeks during the 5 weeks to 13 months age period, for 60 min, with the intensity of 3% of the body weight, 5 times a week; and then performed treadmill exercise until two weeks before the slaughter, for 60 min ,with the speed of 10 m/s, 4 times a week. The mice in the PE underwent treadmill exercise for 8 weeks during 30-38 weeks age period, for 60 min ,with the speed of 10 m/s, 4 times a week. The mice in the AE underwent swimming exercise for 8 weeks during 5 to 13 weeks age period , for 60 min, with the intensity of 3% of the body weight, 5 times a week. The mice in the BC underwent no exercise for the entire experiment. All animals were sacrificed by intravenous bloodletting after 11 months of feeding. Dual-energy x-ray absorptiometry was used to estimate the Bone Mineral Density(BMD), Bone Mineral Content(BMC) and body composition. RESULTS: A total of 37 mice completed the study.(1) The growth rate of BMD in the AE group(0.140±0.117g/cm2/d,P<0.05) was higher than in the other groups during 13-19 weeks age period. (2) Compared with the BC group, the BMD of AE group (0.077±0.019 g/cm2, P=0.011) and LE group (0.065±0.026 g/cm 2 , P =0.011) significantly increased; the muscle mass of LE group (18.222±4.631g, P=0.003), PE group (16.500±5.798g, P=0.010) and AE group (14.700±7.917g, P =0.042) significantly increased; the fat mass and body fat rate of PE group (1.500±4.478g, P=0.003; -22.4±11.3%, P=0.00) and LE group (1.556±3.9721g, P=0.003; -23.5±7.0%, P=0.000) significantly decreased. CONCLUSIONS: The present study demonstrates that:(1)adolescent physical activity can help mice to accumulate peak bone mass;(2) both lifelong exercise and starting exercise at an old age can help prevent fat accumulation and muscle mass reduction.
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