Change in balance ability in day time and the factors in healthy young people using a stabilometer / 体力科学

Maintaining posture and movement stabilities, that is, balance, is particularly important for safety in daily life along with performing exercises. The purpose of this study was to clarify the changes in static and dynamic balance abilities from 8:00 to 18:00 and investigate the factors of change in balance ability among healthy young people. The subjects were nine relatively active healthy university students. The static and dynamic balance abilities were measured by a body sway test while static standing and the Cross Test, in which the center of gravity was voluntarily moved to the maximum in the front, back, left, and right directions, respectively. No change with time was observed in the static balance index. However, the maximum amplitude in the anteroposterior direction, an index of dynamic balance, significantly increased with time (8:00 vs 18:00, p<0.05). Sleepiness score significantly decreased with time (8:00 vs 18:00, p<0.05). As a result of simple correlation analysis, there were significant relationships between static balance indices (environmental area and rectangle area) and autonomic activity index (heart rate variability) at many times (p<0.05). Thus, it was concluded that the static balance ability was not affected by time. Furthermore, the ability to move the center of gravity in the anteroposterior direction of dynamic balance was low during morning and increased with time in relatively active healthy young people. Additionally, it was suggested that autonomic nervous activity was associated with static balance and the sleepiness was associated with dynamic balance.

CARDIOVASCULAR RESPONSE TO STATIC AND DYNAMIC MUSCLE CONTRACTIONS AT EQUIVALENT TENSION-TIME INDICES / 体力科学

In the present study, we examined cardiovascular response to static and dynamic hand-grip exercise at equivalent work load (peak tension) and tension-time index (TTI, integrated tension for time) in healthy young (n=8) and elderly (n=8) males. Static and dynamic exercises were conducted for 75 s and 150 s at 30% of maximal voluntary contraction (MVC) and for 45 s and 90 s at 50%MVC, respectively. Arterial pressure was continuously measured on a beat basis. Blood pressure at the end of exercise and the magnitude of pressor response induced by exercise did not differ significantly between static and dynamic exercises at the two work loads. The magnitude of pressor response tended to depend on work load. These findings were the same in both age groups. Consequently, it was indicated that blood pressure responses to static and dynamic hand-grip exercise at equivalent work load and TTI did not differ both in young and elderly people. Furthermore, it was suggested that central command and muscle metabolite induced stimulation of the exercise pressor reflex during static and dynamic exercise were similar based on the results of relative perceived exertion and blood pressure response during post-exercise arterial occlusion.

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.

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.

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.