Effects of periodic hypobaric hypoxic environments on physiological responses during endurance exercise and recovery after exercise / 体力科学

<p>We developed a periodic hypobaric hypoxic environment (PHHE) system. Characteristics of this system varied between decreased pressure at an altitude of 1,500 m for 180 seconds and increased pressure at an altitude of 0 m for 180 seconds. The present study aimed to determine the effects of PHHE on physiological responses during endurance exercise and recovery after exercise. This study included 12 healthy men, and they provided written informed consent. All subjects performed a cycling exercise for 30 minutes and recovered after exercise for 10 minutes. The exercise protocol was performed with 20% maximum oxygen uptake for 6 minutes (warm-up), 40 % for 18 minutes (main exercise), and 20 % for 6 minutes (cool down). We established two experimental conditions: exercise with the PHHE and the control (C). The C condition involved exercise using the PHHE at an altitude of 0 m, and the atmospheric pressure was not changed. In the PHHE condition, the atmospheric pressure was changed periodically from 967 to 817 hPa (the external pressure was 1,008 hPa). Subjects’ heart rate (HR), blood pressure (BP), arterial oxygen saturation (SpO₂), rating of perceived exertion, and respiratory responses were measured in both conditions. The SpO₂, HR and systolic BP during exercise were significantly lower in the PHHE condition than in the C condition. The HR post-exercise was significantly lower. After exercise, the ln HF, an index of cardiac parasympathetic nervous system modulation, was significantly higher. In conclusion, during endurance exercise, cardiocirculatory responses in the PHHE condition were decreased.</p>

RELATIONSHIP BETWEEN MUSCLE PROPORTION AND QUANTITY OF EXTREMITIES IN YOUNG JAPANESE WOMEN / 体力科学

Recently, a long-term health concern has been identified in young Japanese women. These women have a high percentage of body fat despite a normal shape index indicator such as BMI. This condition is called marked obesity, and shows relative low lean body mass. Using an analogous determination, we investigated low percentage of muscle quantity (LM) in the extremities of young Japanese women (n=156) . The cross-sectional areas of muscle, subcutaneous fat, and bone were measured in the upper arm and thigh using ultrasonography. Extremity shape index (CSA<SUB>t</SUB>/L) was defined as the total extremity cross-sectional area (CSA<SUB>t</SUB>) divided by the length of the limb (L), Percent muscle in each extremity (% MA) was calculated from the ratio of muscle CSA to whole limb CSA. LM was defined as the percentage of muscle in the upper arm or thigh less than 1 SD below average and the limb shape index less than 1 SD above average. Nine of 91 subjects displayed LM for the upper arm. A similar proportion of subjects showed LM for the thigh (15/156) . The muscle mass and strength in the upper arm or thigh were compared between the subjects with LM and non-LM subjects with a similar shape index of extremity. There was a tendency towards lower muscle mass and muscle strength in the subjects with LM. From the same comparison, the subjects with LM showed a greater load on extremity muscles to sustain the body weight (i.e., body weight per unit of upper arm or thigh muscle CSA) . To mitigate the deleterious health consequences of low percent muscle quantity it is recommended that young Japanese women who display such a condition should participate in a resistance-training program.