Recovery of respiratory cardiac cycle variability after strenuous exercise / 体力科学

A study was conducted to examine the recovery of vagal activity after strenuous exercise based on changes in the magnitude of respiratory cardiac cycle variability, changes in the phase of this variability and the mechanism of the change. Six healthy male university students were studied for 5 h after exhaustive treadmill running. For cardiac cycle (RR) and blood pressure, the magnitude of respiratory variability and phase difference between respira-tory variability and respiration were measured. Respiratory period and tidal volume were maintained at 6 s and 21, respectively.<BR>1. The amplitude of respiratory RR variability decreased markedly after exercise and returned almost to normal after 2 h of recrvery. The phase of RR delayed with exercise, proceeded rapidly 2 h after exercise and progressively after that.<BR>2. The amplitude and phase of respiratory systolic blood pressure variability were almost stable before and after exercise.<BR>Based on these results, we conclude that vagal activity inhibited by strenuous exercise recovers about 2 h after the end of exercise. The delay in the phase of respiratory cardiac cycle variability with exercise may reflect inhibition of vagal activity.

Study of human muscle circulation during bicycle exercise using near-infrared spectroscopy / 体力科学

Using near-infrared spectroscopy, we monitored changes of oxygenated hemoglobin and myoglobin contents [oxy (Hb+Mb) ], deoxygenated hemoglobin and myoglobin contents [deoxy (Hb+Mb) ], and total hemoglobin and myoglobin contents [total (Hb+Mb) ] of the thigh muscle at rest and during incremental bicycle exercise and recovery in 10 healthy male volnuteers. Gas exchange parameters were also measured in breath-by-breath mode.<BR>The following results were obtained :<BR>1) During low-intensity exercise (216 kpm/min), oxy (Hb+Mb) increased, while deoxy (Hb+Mb) and total (Hb+Mb) decreased. These changes are thought to reflect an increase in arterial blood flow to the exercising muscle and an increase in venous return.<BR>2) During high-intensity exercise (above 972 kpm/min), oxy (Hb+Mb) decreased, while deoxy (Hb+Mb) increased. These findings probably reflect increased O<SUB>2</SUB>extraction.<BR>3) Upon cessation of exercise, oxy (Hb+Mb) and total (Hb+Mb) increased, and deoxy (Hb+Mb) decreased abruptly. These changes probably reflect post-exercise hyperemia with decreased O<SUB>2</SUB>extraction.<BR>4) Oxy (Hb+Mb) level at ventilatory threshold (VT) was the same as or higher than that of resting condition, indicating that VT occurs when the level of O<SUB>2</SUB>in the vessels of the thigh muscle is relatively high.<BR>5) Spontaneous fluctuation of oxy (Hb+Mb) with frequency of 7-10 cycles/min was observed. This fluctuation was more marked during exercise than during rest or recovery.<BR>These findings suggest that the influence of increased blood flow and venous return on oxy (Hb+Mb), deoxy (Hb+Mb) and total (Hb+Mb) are greater than that of O<SUB>2</SUB>extraction during low intensity exercise, whereas the influence of O<SUB>2</SUB>extraction increases with exercise intensity.<BR>Near-infrared spectroscopy provides valuable information with regard to O<SUB>2</SUB>transport and O<SUB>2</SUB>extraction in the exercising muscle.

Relationship between sympathetic and adrenomedullary activities during exercise. With reference to duration of exercise / 体力科学

This study was designed to evaluate the effect of exercise duration on the relation between sympathetic and adrenomedullary activities. Six trained subjects completed the following two exercise protocols ; six 2-min exercise sessions at 100% maximal O<SUB>2</SUB>uptake (VO<SUB>2</SUB>max) interspersed with 10-min recovery periods, and three 10-min exercise sessions at 80%VO<SUB>2</SUB>max interspersed with 10-min recovery periods. Plasma noradrenaline (NA), plasma adrenaline (A), NA/A ratio (NA/A), heart rate (HR), coefficient of variation of R-R intervals (CVRR) and blood lactate (La) were measured. With repetition of exercise sessions in both protocols, HR, NA and A gradually increased. CVRR rapidly decreased at the first exercise session and remained unchanged thereafter. NA/A increased by the first exercise session, but decreased by the following exercise sessions. NA in the second exercise session at 100%VO<SUB>2</SUB>max was significantly lower than that in the first. We conclude that, at the beginning of exercise, the increase of sympathetic activity is more dominant than that of adrenomedullary activity, whereas, with prolongation of exercise duration, the increase of adrenomedullary activity becomes more dominant than that of sympathetic activity,

Relationship between respiratory period and respiratory cardiac cycle variability. The influence of respiratory blood pressure variability / 体力科学

This study was undertaken to clarify the influence of respiratory blood pressure variability upon the relationship between respiratory period and respiratory cardiac cycle variability. In 4 healthy male university students respiratory period was varied over the range of 6-20 sec while tidal volume was maintained constant (21) and in 5 other male students tidal volume was varied over the range of 1.0-2.5<I>l</I> while respiratory period was maintained constant (6 sec) . For cardiac cycle (RR) and systolic and diastolic blood pressure (SBP and DBP), amplitude of respiratory variability and phase difference between respiratory variability and respiration were measured.<BR>1. Patterns of change of amplitude of RR and of SBP were similar when respiratory period was changed.<BR>2. When respiratory period was short (6sec), RR was nearly in phase with SBP. However, as respiratory period increased, the phases of RR and SBP had a tendency to proceed, with the tendency being more pronounced in the latter. Thus, when respiratory period was prolonged (20 sec), SBP led RR.<BR>3. Phase relationship between respiratory SBP variability and respiration did not change when tidal volume was changed.<BR>4. Respiratory DBP variability became more marked as respiratory period increased, and showed more marked phase shift than did respiratory SBP variability. Therefore, of those parameters DBP occurred earlier.<BR>Based on these results, it is concluded that respiratory RR variability is closely related to respiratory SBP variability when respiratory period is changed, but that the phase difference between RR and SBP reflects the effect of pulmonary stretch reflex which is dependent on respiratory period.

Heart rate and plasma catecholamines responses to exercise at various intensities / 体力科学

To investigate the responses of heart rate and plasma catecholamines to exercise at various intensities, seven healthy adult males performed 6-min bouts of cycling exercise at 30, 50, 70 and 90% of maximal oxygen consumption (VO<SUB>2</SUB>max) . Heart rate (HR), plasma noradrenaline (NA), plasma adrenaline (A), blood lactate (La) and coefficient of variation of R-R intervals (CVRR) were determined i n each case.<BR>The following results were obtained:<BR>1) CVRR showed a sharp decline to the extent of 50%VO<SUB>2</SUB>max, then fell more slightly for heavier exercise.<BR>2) NA and A significantly increased from resting value at 50%VO<SUB>2</SUB>max, and followed by further increase with exercise intensity. NA/A increasd in proportion to exercise intensity.<BR>3) The results of multiple regression analysis of HR (dependent variable) and NA, A and CVRR (independent variables) indicated the greatest standardized partial regression coefficient for CVRR in the case of low intensity exercise, and for NA with high intensity exercise.<BR>4) La increased abruptly at 70%VO<SUB>2</SUB>max, whereas NA and A rose drastically at 90%VO<SUB>2</SUB>max.<BR>The conclusion based on these results is as follows: HR is mainly influenced by change in parasympathetic tone to the extent of 50%VO<SUB>2</SUB>max, whereas sympathetic and adrenomedullary activity are the main factors controlling HR in heavier exercise. Within the submaximal level of exercise, sympathetic activity increases more markedly than that of adrenomedullary activity. Abrupt increase in La may be independent of catecholamines.

Relationship between accelerated plethysmogram, blood pressure and arteriolar elasticity / 体力科学

The relationship between arterial blood pressure and accelerated plethysmogram (APG) obtained by differentiating two times digital plethysmogram was studied in five healthy male university students. Finger arterial blood pressure was found to change by inflating the cuff of a sphygmomanometer placed on the upper arm followed by gradual deflation. APG and blood pressure were analyzed in the beat by beat mode. Room temperature was maintained at 23-24°C.<BR>The following results were obtained :<BR>1) Component“a”of APG became higher, and“b”and“e”components became increased with systolic blood pressure (SBP) .<BR>2) Component“a”of APG decreased, as did also“b”and“e”components with increase in diastolic blood pressure (DBP) and arteriolar elasticity.<BR>3) The two mechanisms for increase in SBP were increase in blood volume, and increase in peripheral resistance. The wave pattern of APG (A-G) changed from G to A by the former, and A to G by the latter.<BR>These findings clearly show the relationship between APG and arterial blood pressure depend on the particular mechanism involved. The simultaneous mesurement of APG and blood pressure may serve as a useful means for measuring peripheral hemodynamics.

Circulatory responses to sudden strenuous exercise. A study by mechanocardiographic method / 体力科学

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.<BR>Six healthy male students volunteered for the study. A bicycle ergometer was prepared for SSE. The intensity and duration of SSE were 100%VO<SUB>2</SUB>max and 1 min, respectively. Warming-up consisting of 80%VO<SUB>2</SUB>max 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.<BR>The main results obtained were as follows :<BR>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 (QS<SUB>2</SUB>), left ventricular ejection time (LVET) or preejection time (PEP) .<BR>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 QS<SUB>2</SUB> shortend and QT/QS<SUB>2</SUB> increased temporarily.<BR>These results suggest the following conclusions :<BR>1) Notch formation observed in heart rate is due to the temporary extension of DT at the early stage of SSE.<BR>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.

Relationship between respiratory period and respiratory arrhythmia / 体力科学

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.<BR>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.<BR>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) .<BR>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.<BR>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.

Effects of prolonged kendo practice in a hot environment on cardiovascular function / 体力科学

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.

Effects of warming-up on circulatory responses to sudden strenuous exercise / 体力科学

A study was conducted to elucidate the changes in circulatory responses to sudden strenuous exercise (SSE) using beat-by-beat analysis of heart rate (HR), stroke volume (SV) and blood pressure (BP) . The effects of warming-up on these responses were also studied.<BR>Six healthy male students volunteered for the study. A bicycle ergometer was prepared for SSE. The intensity and duration of SSE were 100% VO<SUB>2</SUB>max and 1 min, respectively. Warming-up of 80% VO<SUB>2</SUB>max for 5 min followed by SSE. The interval between SSE and warming-up varied from 5 to 30 min. A control experiment was also performed without warming-up.<BR>The main results obtained were as follows :<BR>1) BP decreased in the initial stage of SSE, followed by a steep increase. This temporary drop in BP was prevented by warming-up. This might contribute to the prevention of myocardial ischemia which is occasionally observed in the initial stage of SSE without warming-up.<BR>2) Time constants of HR and SV during SSE were shortened by warming-up with long intervals, while the time constant of BP was shortened when the interval was short.<BR>3) The recovery response of each parameter was accelerated by warming-up, but the effect of warming-up had almost disappeared after a 30 min interval.<BR>These results suggest the following conclusions :<BR>Warming-up accelerates the up-stroke and recovery of circulatory responses to SSE, but these effects of warming-up are strongly influenced by interval time. In particular, the effect of recovery acceleration is almost abolished by a 30 min interval.

Respiratory respones to sinusoidal work load in man. Relationships among amplitude respones, phase response and aerobic capacity / 体力科学

Amplitude and phase response of ventilation (V<SUB>E</SUB>), carbon dioxide output (VCO<SUB>2</SUB>) and oxygen uptake (VO<SUB>2</SUB>) during sinusoidally varying work load for periods (T) of 1-16 min were studied in six healthy men. The relationships between these parameters and aerobic capacity (VO<SUB>2</SUB>max, ATVO<SUB>2</SUB>) were also examined. The results and conclusions obtained were as follows:<BR>(1) The relationship between the period (T) of exercise and amplitude response of VO<SUB>2</SUB>, VCO<SUB>2</SUB> and V<SUB>E</SUB> was well described by first-order exponential models. However, the relationship between the period of exercise and the phase shift (phase responses of VO<SUB>2</SUB>, VCO<SUB>2</SUB>, and V<SUB>E</SUB>) was better described by complex models comprising a first-order exponential function and a linear equation. This can be explained by Karpman's threshold theory.<BR>(2) High negative correlations were observed between the steady-state amplitude (A) of phase response or the time constants (r) of amplitude response and VO<SUB>2</SUB>max, and ATVO<SUB>2</SUB>. Significantly high negative correlations for all gas exchange parameters may be more rapid in individuals with greater aerobic capacity.<BR>(3) A close relationship between the response of VCO<SUB>2</SUB> and V<SUB>E</SUB> was demonstrated by a higher correlation coefficient than that between VO<SUB>2</SUB> and VCO<SUB>2</SUB> or between VO<SUB>2</SUB> and V<SUB>E</SUB>. This can be partly, but not completely, explained by the cardiodynamic theory.

Changes in systolic and diastolic time intervals during prolonged exercise. (Part 3) / 体力科学

A study was undertaken to elucidate the mechanism responsible for the specific changes in systolic time intervals (STIs), diastolic time (DT) and the ratio of total electromechanical systole to DT (QS<SUB>2</SUB>/DT), which were observed during prolonged exercise<SUP>17, 19)</SUP> Sixteen healthy male students performed short-term incremental maximal exercise and 40-min submaximal exercise with a work load requiring 65% of maximal oxygen consumption on a bicycle ergo-meter, Heart rate (HR), stroke volume (SV), blood pressure (BP), STIs and DT were calculated from electrocardiogram, phonocardiogram, derivative of ear densitogram, impedance cardiogram and finger arterial pressure wave.<BR>1) During the short-term exercise, STIs, DT and QS<SUB>2</SUB>/DT changed rectilinearly in accordance with increased HR, whereas they changed in a specific zigzag pattern during the prolonged exercise.<BR>2) During the prolonged exercise, SV and BP were lower than those during the short-term exercise, except for SV between 1 and 2 min after the start of the exercise. From 2 min onwards, left ventricular ejection time (LVET), QS<SUB>2</SUB> and QS<SUB>2</SUB>/DT became smaller than those during the short-term exercise.<BR>3) Differences between the measured values of LVET, pre-ejection period (PEP) and PEP/LVET and those predicted by multiple regression equations during the prolonged exercise were smaller than those during the short-term exercise.<BR>From these findings, it was concluded that the specific changes observed in STIs, DT and QS<SUB>2</SUB>/DT during prolonged exercise are produced by decrease of SV and BP in the early stage, and probably influenced by a decrease in myocardial contractility in the late stage.

Changes in systolic and diastolic time intervals during prolonged exercise. (Part 2) / 体力科学

A study was undertaken to determine whether the specific change in the ratio of systolic to diastolic time (QS<SUB>2</SUB>/DT) observed during prolonged exercise<SUP>17)</SUP> is dependent on HR or elapsed time, and also to elucidate the possible relationship between change in QS<SUB>2</SUB>/DT and distance-running performance. Twelve male distance runners were divided into two groups, a high- (HP Group) and a low-performance (LP Group) group, according to their 10, 000-meter running performance. They performed 60-min exercise on a bicycle ergometer at a work load controlled so as to keep the HR at 150 bpm. HR, systolic time intervals (STIs) and DT were calculated from electrocardiogram, phonocardiogram and the derivative of ear densitogram.<BR>In the time course of QS<SUB>2</SUB>/DT, two crests were formed at 2 and 15 min after the start of exercise, and also two troughs were formed at 10 and 20 min. Some of these troughs and crests formed even when HR was kept constant. Patterns of change in QS<SUB>2</SUB>, DT, QS<SUB>2</SUB>/DT and other parameters were similar in the two groups. However, the absolute values of the parameters differed. QS<SUB>2</SUB>, left ventricular ejection time (LVET) and QS<SUB>2</SUB>/DT in the HP Group were lower than those in the LP Group, whereas DT in the HP Group was longer than that in the LP Group.<BR>From these findings, it was concluded that the specific change seen in QS<SUB>2</SUB>/DT during prolonged exercise is dependent not on the HR level but on elapsed time. The changes in STIs and DT during prolonged exercise are thus influenced by the distance-running performance of the subjects.

Breath-by-breath differences between exercise gas exchange kinetics measured at the mouth and those estimated at the alveolar level / 体力科学

In order to study respiratory transients during exercise, we examined breath-by-breath differences between gas exchange kinetics measured at the mouth and those estimated at the alveolar level. The gas exchange data at the mouth were obtained by measurement of expired gases only (expiratory flow method) . Correction for breath-by-breath changes in lung gas stores was applied to the total gas exchange, which was obtained by subtracting expired from inspired gas volume (alveolar gas exchange method) . Constant work loads (150, 200, 250 W) and a ramp work load (30 W/min) preceded and followed by a 50 W load were generated by a computerized cycle ergometer. Best-fit first- or second-order model values for gas exchange kinetic parameters were found by the non-linear least-squares method.<BR>1. Regardless of work intensity and forcing function, the breath-by-breath variation in gas exchange measured at the mouth was larger than the gas exchange estimated at the alveolar level, in both a non-steady state and a steady state. The variation was caused by the invalidity of assuming zero N<SUB>2</SUB> exchange at the mouth, which was attributed to changes in lung volume.<BR>2. Vo<SUB>2</SUB> kinetics at the alveolar level were faster than those at the mouth, while the converse held for Vco<SUB>2</SUB> at the onset of constant load work, due to the effects of fluctuations in lung gas stores on the kinetics of gas exchange at the mouth. During ramp load work, Vo<SUB>2</SUB> and Vco<SUB>2</SUB> kinetics at the alveolar level were faster than those at the mouth.<BR>3. Steady state gas exchange values at the alveolar level and at the mouth were the same during constant load work, since the lung gas stores corrections added up to small fractions of the total gas exchange when summed over the long term.<BR>4. Consideration of both the proper end-expiratory lung volume and ventilationperfusion inhomogeneity was required in order to estimate the true alveolar gas exchange.

Measurement of left ventricular ejection time utilizing the derivative of the ear densitogram / 体力科学

A study was performed to investigate the validity of the derivative of the ear densitogram for measurement of left ventricular ejection time (LVET) .<BR>Nine male college students performed bicycle exercise at an initial work load of 0 watt (W), subsequently increasing by 60W every 3 min up to 240W. The LVET derived from the derivative of the ear densitogram (LVETe) was compared with that derived from the carotid pulse wave (LVETc) obtained at the same time.<BR>The results were as follows:<BR>1. There was a high correlation coefficient, r=0.987 (P<0.01), between LVETe and LVETc.<BR>2. At rest, LVETe showed a tendency to coincide with LVETc. In contrast, LVETe became longer than LVETc during exercise, and the higher HR became, the larger the difference between the two.<BR>3. In the individual regression equations between LVETe and LVETc, the slopes and the intercepts were nearly identical.<BR>4. The following equation was proposed for the correction of LVETe during exercise. LVET=-0.147⋅HR+ LVETe+ 8.3<BR>From these findings, it was concluded that the validity of the derivative of the ear densitogram for estimation of LVET is sufficiently high. LVETe at rest is valid for the estimation of LVET without correction. During exercise, however, LVETe shows a tendency to be longer than LVETc, and thus it is desirable to correct LVETe using the above equation.

Systolic and diastolic time intervals during prolonged exercise of a constant intensity / 体力科学

The purpose of this study was to elucidate the changes in systolic and diastolic time intervals which accrue along with increase of HR during a prolonged exercise.<BR>Fifteen male collegiate distance runners performed bicycle ergometer exercise of 70% maximal oxygen intake for 60 minutes. Electrocardiogram, phonocardiogram, pulse wave using ear densitogram and its derivative were recorded throughout the exercise, and then HR, STI, DT (diastolic time) and QS<SUB>2</SUB>/DT were caluculated from the tracings.<BR>The results obtained are as follows:<BR>1. At the initial phase of the exercise, DT decreased markedly to result in rapid increase of QS<SUB>2</SUB>/DT. When HR was between 130-150 beats/min, however, the rate of decrease of QS<SUB>2</SUB> was greater than that of DT, so QS<SUB>2</SUB>/DT showed a tendency to decrease. When HR was more than 150, QS<SUB>2</SUB> reached a plateau but DT still continued to decrease, and QS<SUB>2</SUB>/DT turned to increase again.<BR>2. LVET decreased slowly throughout the exercise, whereas PEP decreased rapidly within initial two minutes and kept a steady state thereafter. The change in QS<SUB>2</SUB> after two minutes of exercise seemed to depend on LVET.<BR>3. LVETi and QS<SUB>2</SUB>i showed a similar change as that in QS<SUB>2</SUB>/DT but the change in QS<SUB>2</SUB>i was less obvious than that in LVETi.<BR>4. PEN and PEP/LVET decreased rapidly in the initial two minutes, thereafter they continued to increase more slowly with increase of HR until the end of exercise.<BR>Conclusively, HR continued to increase monotonously during prolonged exercise of a constant intensity, while systolic and diastolic time intervals varied the directions and patterns of their changes during the exercise.

Change of postural control while repeatedly imposing horizontal floor vibration in upright stance / 体力科学

This study was designed to investigate the change of postural control while repeatedly imposing the horizontal floor vibration in upright stance. A vibration table mounted with a force platform was vibrated sinusoidaly in anteroposterior direction under the condition of 2.5 cm amplitude and 0.5 Hz frequency. Ten female subjects, aged from 18 to 21 years, were equally divided into O-group and C-group. The subjects maintained the standing posture on the vibration table, for one minute with open and closed eyes in both groups in the first trial, for two minutes with open eyes in O-group and with closed eyes in C-group in the 2 nd to 11 th trials, and for one minute with closed eyes in O-group and open eyes in C-group in the 12th trial. The fluctuation of the center of foot pressure (CFP) in anteroposterior direction and EMGs of m. tibialis anterior and m. gastrocnemius were analyzed. The controllability of standing posture was evaluated by the mean speed of the CFP fluctuation. The muscle activity was examined with EMGs. The results were summarized as follows :<BR>1) In a great number of subjects, the controllability of standing posture rapidly improved till the 3rd trial in each eye condition, while after the 3 rd trial changes of controllability were relatively small. Accordingly, it was suggested that by investigating the change of controllability for 5 trials, we could sufficiently detected an individual difference of the learning ability of postural control.<BR>2) At the beginning of the practice, the controllability with open eyes was greatly superior to that with closed eyes. Although the difference of controllability between open and closed eyes decreased with advance of practice, in the 11 th trial that difference was obviously observed.<BR>3) In a great number of subjects, the phase lag of the CFP fluctuation to the floor vibration increased till the 3rd trial according to improving controllability. In some subjects, the change of controllability was relatively small, the change of phase lag was small and also, correlations between the postural controllability and the phase lag weren't significant.<BR>4) M. gastrocnemius was active when the CFP fluctuated forward and m. tibialis anterior when the CFP fluctuated backward greatly. In each eye condition, the magnitude of muscle activity decreased with practice and m. tibialis anterior was inactive in a great number of subjects in the last stage of the practice.<BR>5) The controllability with open eyes didn't show a significant change after practice with closed eyes. By contrast, the controllability with closed eyes improved greatly after practice with open eyes and was approximately equal to that in the last stage of practice with closed eyes.

A STUDY OF MUSCLE PUMP / 体力科学

The purpose of this study was to investigate the effects of contraction force and the pooled blood volume in the calf on the pumping action of calf muscle contraction. Calf blood volume was controlled by lower body negative pressure (LBNP) and isometric contraction of calf extensor muscle was performed using a handmade dynamometer in recumbent position. The relative volume changes (ΔV/V%) of calf were determined using rubber straingage, when isometric contractions (5, 10, 20, 40 and 60 kg) of the calf muscle were repeated under LBNP of 0, -20, -40, and -60 mmHg.<BR>During resting condition, Δ V/V was increased by 1.04% under -20 mmHg LBNP, 1.88% under -40 mmHg, and 2.54% under -60 mmHg. These increases of ΔV/V were due to the increased blood pooling in the calf. It was shown that the increased blood volume was almost expelled by several bouts of muscle contractions of proper force. The optimum force of contractions for expelling pooled blood was 20 kg under -20mmHg LBNP, and 40 kg under -40 and -60 mmHg LBNP. And it was apparent that the effectiveness of muscle pump was accumulated with repeating contractions, arriving to a plateau after several bouts.<BR>It was shown that the effect of muscle pump in the given contraction force was more effective under the condition with more amount of blood contained in the calf, but the muscle pumping action by light contraction forces couldn't overcome the effect of severe LBNP.

A study of muscle pump. Relationship between contraction force and blood volume and pumping action / 体力科学

The purpose of this study was to investigate the effects of contraction force and the pooled blood volume in the calf on the pumping action of calf muscle contraction. Calf blood volume was controlled by lower body negative pressure (LBNP) and isometric contraction of calf extensor muscle was performed using a handmade dynamometer in recumbent position. The relative volume changes (ΔV/V%) of calf were determined using rubber straingage, when isometric contractions (5, 10, 20, 40 and 60 kg) of the calf muscle were repeated under LBNP of 0, -20, -40, and -60 mmHg.<BR>During resting condition, Δ V/V was increased by 1.04% under -20 mmHg LBNP, 1.88% under -40 mmHg, and 2.54% under -60 mmHg. These increases of ΔV/V were due to the increased blood pooling in the calf. It was shown that the increased blood volume was almost expelled by several bouts of muscle contractions of proper force. The optimum force of contractions for expelling pooled blood was 20 kg under -20mmHg LBNP, and 40 kg under -40 and -60 mmHg LBNP. And it was apparent that the effectiveness of muscle pump was accumulated with repeating contractions, arriving to a plateau after several bouts.<BR>It was shown that the effect of muscle pump in the given contraction force was more effective under the condition with more amount of blood contained in the calf, but the muscle pumping action by light contraction forces couldn't overcome the effect of severe LBNP.

Effect of muscle pump on hemodynamics. (Part 3). Transient changes at the start and end of exercise during LBNP / 体力科学

In order to evaluate the effect of muscle pump on blood circulation at the start and end of exercise, cardiac responses to pedaling exercise at 75 watt in the supine position were investigated under lower body negative pressure (LBNP) of -60mmHg. Six healthy male college students volunteered for subjects. Cardiac output (Q), stroke volume (SV), thoracic impedance (ZO) and heart rate (HR) were determined by using ensemble-averaged impedance cardiogram and ECG.<BR>The results obtained were as follows.<BR>1) By the initiation of exercise under LBNP, SV and Q promptly and more markedly increased and ZO decreased than the control experiment which were done under normal pressure. These changes were suggested to be caused by mobilization of previously pooled blood in the legs by muscle pump. Effects of muscle pump arrived to a plateau within about 30 sec after the start of exercise. And these effects were immediately disappeard by the cessation of exercise.<BR>2) By the release of LBNP during resting condition, the same changes were observed in SV, Q and ZO as in the start of exercise under LBNP. However HR decreased in the case while it increased in the case of exercise in LBNP. This difference in HR might be the result of the chronotropic effects by the exercise.<BR>3) In the very early phase of exercise in the control exercise, SV decreased and ZO increased. These changes were probably caused by superiority of chronotropic action by the exercise to increase in venous return in this position.<BR>These results led us to a conclusion that the effect of muscle pump appeares immediately by the start of the exercise and it arrives at plateau within about 30 sec. This effect is immediately disappeared by the cessation of exercise.