Effects of nasal breathing on partial pressure of carbon dioxide in arterial blood during prolonged exercise in a hot environment / 体力科学

Prolonged exercise in a hot environment increases the minute ventilation (VE) and respiratory rate (RR) with an increase in core temperature. This hyperthermia-induced hyperventilation decreases the partial pressure of arterial blood carbon dioxide (PaCO2). Conversely, nasal breathing during exercise has been reported to produce low VE and RR values and high PaCO2 values; however, no studies have investigated this in hot environments. Therefore, the purpose of this study was to clarify the effect of nasal breathing on estimated partial pressure of carbon dioxide in arterial blood (PaCO2,estimate) during prolonged exercise in a hot environment. Twelve university endurance athletes participated in the study and performed a 40-minutes steady-state cycling exercise at an intensity of 55% of peak oxygen uptake in a hot environment (room temperature 35℃, relative humidity 40%). Using randomized crossover design, two experiments were performed—nasal breathing condition (NB) and mouth breathing condition (MB). Moreover, physiological indices were measured during the exercise. Rectal temperature increased in both conditions, but there was no significant difference between these conditions. PaCO2,estimate values were significantly higher in NB between 10 minutes and 40 minutes of exercise (p < 0.05) compared to MB, and decreased with time in MB. Compared to MB, the VE was significantly lower in NB between 30 minutes and 40 minutes (p < 0.05), while the RR was significantly lower in NB between 25 minutes and 40 minutes of exercise (p < 0.05). Therefore, nasal breathing during a prolonged moderate-intensity exercise in a hot environment prevented the decrease in PaCO2,estimate due to hyperthermia-induced hyperventilation.

Effect of temperature for cooling leg on intermittent exercise performance during half-time in a hot environment / 体力科学

Intermittent exercise performance in a hot environment is lower than in temperate conditions. Cooling strategies at rest are important; however, the appropriate cooling temperature is not clear. The purpose of this study was to investigate the effect of temperature for cooling leg during half-time (HT) on intermittent exercise performance. Eleven men performed two pre-tests and three experimental trials of a 2 × 30 min intermittent exercise protocol in the heat (33°C; 50% relative humidity). During HT, three experimental conditions were set: no cooling (CON), cooling at the thigh using 12°C ice packs (COOL), and cooling at the thigh using 0°C ice packs (ICE) for 15 min. During the 2nd half, which consisted of 5 s maximal power pedaling every minute separated by 50 s of unloaded pedaling (80 rpm) and rest (5 s), the subjects repeated 2 × 15 sets of the intermittent exercise protocol. The peak power output under the COOL condition (694 ± 80 W) was significantly higher than that of the CON (653 ± 84 W). Thigh skin and deep temperatures showed a significant difference between each condition. In the COOL, thermal sensation was significantly lower, and thermal comfort was significantly higher. In a protocol that simulates intermittent athletic competitions such as soccer in a hot environment, using ice packs at 12°C to cool the thigh during HT lowered thigh skin and deep temperatures and improved heat perception and intermittent exercise performance. This cooling strategy is practical, suggesting that it would be effective for actual competitive situations.

The associations between physical fitness and body fatness with blood lipid profile in Japanese children and adolescents / 体力科学

<p>The purpose of the present study was to examine the associations between physical fitness and body fatness with blood lipid profile in 231 Japanese children and adolescents (12.1 ± 1.5 years). The primary outcomes of the present study were a lipid risk score which was calculated by summing up z scores of three lipid items (triglycerides, low density lipoprotein-cholesterol, and high density lipoprotein-cholesterol). Physical fitness was assessed by using the Japanese standardised fitness test. For body fatness, a percentage of overweight was calculated with using age-, sex-, height-specific standardised body mass. For combined analysis (fitness × fatness), the participants were cross-tabulated into four groups (Non-Obese/Higher-Fit, Non-Obese/Lower-Fit, Obese/Higher-Fit, and Obese/Lower-Fit). The results demonstrated that the participants in fitness categories A/B [most fit] and C [middle] demonstrated the lower (better) lipid risk score than the participants in fitness categories D/E [least fit] (F _{(2, 222)} = 6.03, p = .003). For body fatness, the lipid risk score in obese group was significantly higher (worse) than that in thin and normal groups (F _{(2, 222)} = 6.08, p = .004). The combined analysis showed that there was a significant interaction (fitness × fatness) on the lipid risk score (F _{(1, 221)} = 4.05, p = .047), suggesting that Obese/Lower-Fit group had the worst risk score compared to the other groups. The present study suggests that improving both fitness and body fatness might be important for better lipid profile in Japanese children and adolescents.</p>

Factors associated with achieving physical activity guideline in Japanese adolescents / 体力科学

Understanding factors associated with physical activity (PA) is important to promote PA. The purpose of the present study was to investigate factors associated with achieving PA guideline in 293 Japanese adolescents (140 boys and 153 girls). Time spent in moderate to vigorous PA (MVPA) was accessed by using accelerometers. Based on MVPA, the participants were classified as “Active” (≥60 min/day of MVPA) or “Inactive” (<60 min/day of MVPA). Anthropometry, age, screen time, mental health, participation in after-school sport activities, sleep status, and breakfast status were measured as factors potentially associated with achieving PA guideline. Adjusted logistic regression analyses revealed that after-school sports activities were positively associated with the probability of being Active for both sexes (odds ratios [ORs] [95% confidence intervals (CI)] = 3.90 [1.13-13.49] for boys, 4.80 [1.80-12.81] for girls). In addition, body fat was negatively associated with a reduced likelihood of being Active for girls (ORs [95%CI] = 0.93 [0.87-0.97]). Two factor ANOVA revealed that those in Inactive group had significantly lower PA levels than those in Active group on both regular curriculum and extra-curriculum (F _{(1, 138)} = 152.50 for boys, F _{(1, 151)} = 181.95 for girls, p < 0.001). In addition, for girls, there was a significant interaction effect between domain (regular curriculum vs. extra-curriculum) and after-school sport activities (F _{(1, 151)} = 4.91, p = 0.028), suggesting that obtaining higher PA levels on extra-curriculum might be difficult for those who do not belong to any after-school sport activities. Therefore, promoting PA on regular curriculum (i.e., physical education lessons and recess) might be alternative ways to increase PA levels for those individuals. Furthermore, special attention may be needed for girls who have higher body fat to promote PA.

Effect of increased physical activities of daily living on postprandial triacylglycerol concentrations in postmenopausal women / 体力科学

Limited evidence was available to support the effect of self-selected activities performed under free-living conditions on postprandial lipaemia, particularly for older adults. Thus, the aim of the present study was to examine the chronic effect of increased physical activity of daily living on postprandial triacylglycerol (TAG) in postmenopausal women. Twenty-eight postmenopausal women, aged 71 ± 4 years (mean ± SD), were randomly divided into two groups: active (n=14) and control (n=14) groups. The participants in the active group were asked to increase their activities above their usual lifestyle levels for 4 weeks; freely deciding the duration and intensity of their chosen activities. The participants in the control group maintained their usual lifestyle for 4 weeks. All participants were asked to wear a uniaxial accelerometer for 4 consecutive weeks. At baseline and after 4 weeks, all participants rested and consumed a standardised breakfast and lunch after a 24-h period of physical activity avoidance. Blood samples were collected in the fasted state (0 h) and at 2, 4 and 6 h after breakfast. After 4 weeks, the participants in the active group increased their step counts by 600 steps/day (from 6979 ± 2057 to 7586 ± 2301 steps/day, p=0.047). There was no difference in the pattern of postprandial TAG response between groups (trial × time interaction, p=0.335). A previous study has suggested that only recent exercise (i.e., 12h before but not 24 h before) appears to facilitate the exercise-induced postprandial TAG lowering effects. Thus, in the present study, postprandial lipaemia was not reduced after performing self-selected activities under free-living in postmenopausal women.