Gas exchange kinetics during constant-load exercise were measured to investigate the possibility that excess CO₂ output during exercise might not be dependent on hyperventilation. Five healthy males performed twelve minutes of cycle exercise, including two minutes of 0 W pedaling, at 20, 40, 50, 60, 70, and 80% of their maximal work rate (WRmax) determined on the basis of preliminary ramp exercise of 30 W/min. Minute ventilation, O₂ uptake, and CO₂ output were measured breath-by-breath. Excess CO₂ output and CO₂ stores were calculated, assuming that the respiratory quotient (RQ) in tissue is constant during constant-load exercise and that the respiratory exchange ratio at the mouth level is equal to the RQ during the steady-state phase. Excess CO₂ output was observed at levels of WR greater than 40% WRmax after initial CO₂ storage, where VC_O2/V_E decreased gradually as though in parallel with the kinetics of CO₂ storage. VO₂/V_E, however, appeared to be constant after the initial peak. These data suggest that V_E is closely correlated with V_O2 rather than V_CO2 during constant-load exercise, indicating that excess CO₂ output to compensate lactate production is independent of hyperventilation.

View full abstract

Respiro-circulatory responses to forearm and calf exercise performed simultaneously were compared with corresponding responses to forearm or calf exercise performed separately in 9 active women aged 21.1 yr on average. Handgrip exercise and plantar flexion were carried out for 60 s in a supine position at a frequency of 60 times·min^-1 and the load was adjusted to 1/3 MVC. Forearm blood flow (FBF) increased to 9.64±1.00 ml·100 ml^-1·min^-1 immediately after handgrip exercise, and calf blood flow (CBF) to 12.72±0.72 ml·100 ml^-1·min^-1 after plantar flexion. These increases in FBF and CBF were not significantly different from those after combined arm and leg exercise. Blood flow to inactive limbs showed no significant changes. Rises in systolic and diastolic blood pressure at the end of exercise were significantly higher after handgrip exercise than after plantar flexion. However, no significant difference was found in mean blood pressure among the three types of exercise. Vo₂ and HR in combined exercise were significantly higher than those during handgrip exercise, but no significant difference was found between combined exercise and plantar flexion.
Thus the present results indicated that the circulation to active limbs was not restricted when exercise was performed at 1/3 MVC, and that inhibitory summation shown in the central respiro-circulatory response to increased active muscle mass could occur without restriction of the peripheral circulation to the active muscle.

View full abstract

The relationship between exercise habit and physical fitness in aged individuals was studied in 179 urban residents aged 60-89 years (82 males and 97 females) by a battery of physical performance tests. Eighty-seven point eight percent of the males and 88, 5% of the females were regularly engaged in some kind of exercise, most frequently walking (45.8% of the males and 37.7% of the females), followed by tending plants, croquet, and light exercise (about 30% each) . More strenuous exercise such as swimming, tennis, and jogging was done by 2-3%. The results of the tests were better in individuals who exercised regularly than those who did not, and the differences were significant in grip strength, breath holding, and total score in the males and in all items except grip strength in the females. Physical performance also differed among those who exercised according to the frequency, duration, and intensity of the exercise, but the differences were smaller than between those who exercised and those who did not. From these findings, relatively mild exercise is considered to be effective for preventing (or delaying) the decline of physical fitness in aged individuals.

View full abstract

To study the effects of prolonged kendo practice in a hot environment on cardiovascular function, certain hemodynamic parameters were measured in 5 male college kendo fencers before and after 1 hour of kendo practice performed at a dry bulb temperature of 30.4t and wet bulb temperature of 26.2°C After kendo practice, body weight was significantly decreased and both hematocrit and blood viscosity were significantly increased. The left ventricular end-diastolic dimension and the left atrial dimension, measured by echocardiography, were significantly reduced after kendo practice, and stroke volume, ejection fraction, and fractional shortening were also significantly decreased after practice. The same fencers were subjected to lower body negative pressure testing designed to reduce the left ventricular end-diastolic dimension to the same degree as kendo practice, and comparable decreases in stroke volume, ejection fraction, and fractional shortening were observed. The ratio of end-systolic wall stress to end-systolic volume index was significantly increased during both kendo practice and lower body negative pressure testing. We conclude that prolonged kendo practice in a hot environment impairs cardiac pump function by reducing preload in parallel with the decrease in venous return, that myocardial contractility may not deteriorate despite marked hemoconcentration, and that fluid intake during practice may prevent deterioration of cardiovascular function.

View full abstract

This study was undertaken to clarify the relationship between respiratory period and respiratory arrhythmia. Five healthy male university students voluntarily changed the respiratory period over a range of 3-30 seconds while maintaining tidal volume constant (; 21) . Maximum and minimum cardiac cycles (RRmax and RRmin) and amplitude of cardiac cycle variability (ΔRR), the difference between RRmax and RRmin, were measured from electrocardiogram and respiratory curve.
1. Amplitude of cardiac cycle variability was small for shorter respiratory periods and increased with respiratory period, attaining maximum at respiratory periods of 8-14 seconds followed by decrease at longer respiratory periods.
2. The time from the onset of inspiration to the minimum cardiac cycle was the same for respiratory periods of 8-14 seconds (about 3.6 seconds) .
3. Phase difference between cardiac cycle variability and respiration was determined at each respiratory period. When the minimum or maximum cardiac cycle coincided with the onset of inspiration, this situation being defined as 0°, RRmin was delayed by 180°, 90°, and 0° at respiratory periods of 2.3, 14.4, and 26.5 seconds, respectively and by 360°, 270°, and 180° at respiratory periods of 2.7, 15.0, and 27.3 seconds, respectively.
Based on these results, respiratory arrhythmia is concluded to be quite stable at respiratory periods of 8-14 seconds. At short respiratory periods, tachycardia was found to occur during inspiration and bradycardia during expiration. During long respiratory periods, bradycardia was noted during inspiration and tachycardia during expiration.

View full abstract

A study was conducted for further investigation of the mechanism of notch formation of heart rate (HR) in sudden strenuous exercise (SSE), and rapid increase in stroke volume (SV) right after SSE which were the questions arised in the prior experiment.
Six healthy male students volunteered for the study. A bicycle ergometer was prepared for SSE. The intensity and duration of SSE were 100%VO₂max and 1 min, respectively. Warming-up consisting of 80%VO₂max for 5 min, preceeded SSE. The interval between SSE and warming-up varied from 5 to 30 min. A control experiment was also conducted without warming-up.
The main results obtained were as follows :
1) Diastolic time (DT) temporarily elongated when a notch of HR was formed at the early stage of SSE. Warming-up prevented this formation. No notch was observed throughout total electromechanical systolic time (QS₂), left ventricular ejection time (LVET) or preejection time (PEP) .
2) DT was prolonged immediately after SSE, while LVET, PEPi (PEP index, Weissler's equation) were shortened. PEP/LVET did not change in the initial stage of the recovery period, while electrical systolic time (QT) and QS₂ shortend and QT/QS₂ increased temporarily.
These results suggest the following conclusions :
1) Notch formation observed in heart rate is due to the temporary extension of DT at the early stage of SSE.
2) Decrease in afterload may be the main cause for the rapid increase in stroke volume after SSE, though other factors such as increase in preload, myocardial contractility and sympathetic tone should also be considered.

View full abstract

To evaluate the changes in muscle energetics following NaHCO₃ intake, we measured the phosphorus-31 nuclear magnetic resonance (³¹P NMR) spectra of human muscle in vivo during exercise. Seven male subjects performed two trials, a NaHCO₃ (Alka, Tr.) and a NaCI trial (Cont. Tr.), on two occasions. ³¹P NMR spectra were obtained serially during leg-elevating exercises. Before and during exercise, the intracellular phosphocreatine (PCr), inorganic phosphate (Pi) and pH were determined from the NMR spectra. The decrease of intracellular pH during exercise showed a tendency to be inhibited by NaHCO₃ intake, and the intracellular pH at the end of the exercise was 6.69 for Alka. Tr, and 6.51 for Cont. Tr. The decline of the PCr/ (PCr+Pi) ratio during exercise was not influenced by NaHCO₃ intake. The PCr/ (PCr+Pi) ratio was related exponentially to the intracellular pH. A remarkable decline of PCr/ (PCr+Pi) ratio occurred until the intracellular pH fell to about 6.7, but did not decrease below that. It was suggested that the intake of NaHCO₃ could decrease the rate of fall in the intracellular pH during exercise, and that the PCr store could be influenced by the intracellular pH when the pH was above 6.7, but not below that level.

View full abstract