The interaction of breath holding and muscle mechanoreflex on cardiovascular responses in breath-hold divers and non-breath-hold divers.

Cardiovascular responses to diving are characterized by two opposing responses: tachycardia resulting from exercise and bradycardia resulting from the apnea. The convergence of bradycardia and tachycardia may determine the cardiovascular responses to diving. The purpose of this study was to investigate the interaction of breath holding and muscle mechanoreflex on cardiovascular responses in breath-hold divers (BHDs) and non-BHDs. We compared the cardiovascular responses to combined apnea and the mechanoreflex in BHDs and non-BHDs. All participants undertook three trials-apnea, passive leg cycling (PLC), and combined trials-for 30 s after rest. Cardiovascular variables were measured continuously. Nine BHD (male:female, 4:5; [means ± SD] age, 35 ± 6 years; height, 168.6 ± 4.6 cm; body mass, 58.4 ± 5.9 kg) and eight non-BHD (male:female, 4:4; [means ± SD] age, 35 ± 7 years; height, 163.9 ± 9.1 cm; body mass, 55.6 ± 7.2 kg) participants were included. Compared to the resting baseline, heart rate (HR) and cardiac output (CO) significantly decreased during the combined trial in the BHD group, while they significantly increased during the combined trials in the non-BHD group (P < 0.05). Changes in the HR and CO were significantly lower in the BHD group than in the non-BHD group in the combined trial (P < 0.05). These results suggest that bradycardia with apnea in BHDs is prioritized over tachycardia with the mechanoreflex, whereas that in non-BHDs is not. This finding implies that diving training changes the interaction between apnea and the mechanoreflex in cardiovascular control.

Effects of eating speed on diet-induced thermogenesis / 体力科学

Overweight or obesity becomes a worldwide public health issue; the global obesity pandemic. Strategies to effectively prevent overweight and obesity are needed. Slow eating, which involves chewing food slowly and thoroughly, can be an effective strategy to prevent overweight and obesity. Previous studies reported a relationship between rapid eating and overweight. Candidate factors inducing the relationship have been thought to be related to increases in appetite and energy intake through rapid eating, allowing the ingestion of a greater-than-optimal volume of food. While the counter effect of slow eating has been widely known, effects of eating speed on digestion, absorption, and metabolism has yet to be elucidated. If eating speed affects digestion, absorption, and metabolism, eating speed can be a factor explaining the relationship between eating speed and body composition. The present review is to summarize the effects of eating speed on digestion, absorption, and metabolism, consequently suggesting preferable effects of slowly eating on increasing energy expenditure after eating.

Effect of exercise intensity on autonomic nervous system activity during and after acute exercises / 体力科学

A study was conducted to investigate the effect of exercise intensity on the recovery of autonomic nervous activity after exercise. Ten subjects performed four kinds of 10-min cycle exercise with target heart rates of 100, 120, 140, and 160 beats/min (THR 100, THR 120, THR 140 and THR 160, respectively) following 5 min of exercise to increase the heart rate to the target level. The beat-by-beat variability of the R-R interval was recorded throughout the experiment including the 5-min pre-exercise control period and the 30-min recovery period. Spectral analysis (fast Fourier transform) was applied to every 5-min R-R interval data set before, during ( 5-10 min) and after exercise at the target heart rate. The low- (0.05-0, 15 Hz : P<SUB>1</SUB>) and high- (0, 15-1.0 Hz : P<SUB>h</SUB>) frequency areas were calculated to evaluate sympathetic (SNS) and parasympathetic (PNS) nervous activities as P<SUB>1</SUB>/P<SUB>h</SUB>and P<SUB>h</SUB>, respectively. During exercise, SNS of THR 160 was significantly higher, and PNS of THR 140 and THR 160 was significantly lower than the respective pre-exercise values (p<0.05) . Althouglt all indicators recovered to, or overshot the pre-exercise values at 20-30 min after THR 100 and THR 120, heart rate and SNS were still higher and PNS was still lower than the pre-exercise value after THR 160. These results suggest that the recovery of cardiac autonomic nervous activity is slower after high-intensity exercise than after low-intensity exercise, and that the recovery of autonomic nervous activity after acute exercise does not always corrrespond linearly on the exercise intensity.