Cardiac output and active limb blood flow responses to unilateral and bilateral dynamic handgrip exercise / 体力科学

The purposes of this study were 1) to determine cardiac output and active limb blood flow responses to unilateral and bilateral dynamic handgrip exercises and 2) to investigate the effects of exercise intensity and a change in active muscle mass on the relationship between limb blood flow and cardiac output. Five physically active women performed dynamic handgrip exercises with the right hand (right handgrip exercise ; RHG), with the left hand (left handgrip exercise ; LHG), and bilaterally (bilateral handgrip exercise ; BHG) . Exercise intensities were 10%, 30% and 50% of the subjects' maximum voluntary contraction (MVC) and the exercise frequency was 60 contractions per minute. The 10%MVC exercise duration was 10 min, while the 30% and 50%MVC exercise conditions were performed to exhaustion. During exercise, stroke volume (SV) and heart rate (HR) were measured using Doppler ultrasound and electrocardiogram (ECG), respectively. Cardiac output (Q<SUB>sys</SUB>) was calculated as the product of SV and HR. Blood flow to the forearm (Q<SUB>foream</SUB>, ) was measured by venous occlusion plethysmography. Q<SUB>sys</SUB>, did not differ significantly between RHG, LHG and BHG. However, SV was lower in BHG than in RHG and LHG. Reciprocally, HR was higher during BHG than RHG and LHG. The increase in the Q<SUB>forearm</SUB>, was significantly lower during BHG than RHG and LHG exercise (p<0.05) .<BR>These results suggest that Q<SUB>sys</SUB>, does not differ between unilateral and bilateral handgrip exercise, despite the increase in active muscle mass. The unchanged Q<SUB>sys</SUB> could be explained by the Q<SUB>forearm</SUB> reduction during BHG. The Q<SUB>forearm</SUB> was lower during BHG than during the unilateral handgrip exercises, possibly due to vasoconstriction induced by BHG exercise.

Difference in oxygen supply-consumption balance in thigh muscles working together during knee-extension exercise / 体力科学

The purpose of this study was to clarify the changes in oxygen kinetics in two different thigh muscles recruited for dynamic knee-extension exercise at varying intensities in seven female subjects. Pulmonary oxygen uptake (Vo<SUB>2</SUB>) was measured by the 10-s mixing chamber method. Changes in oxygenated hemoglobin (HbO<SUB>2</SUB>), deoxygenated hemoglobin (Hb), and total hemoglobin (HbT) contents were measured in the vastus lateralis (VL) and rectus lemons (RF) muscles using near-infrared spectroscopy, and the oxygen saturation (SO<SUB>2</SUB>) was calculated as the HbO<SUB>2</SUB> divided by HbT in percent. The surface electromyograms (EMG) of both muscles were also recorded. The integrated EMGs (iEMG) of the VL and RF increased linearly with increasing exercise intensity up to 100%VO<SUB>2peak</SUB>. However, the HbO<SUB>2</SUB> and Hb remained unchanged when exercise intensity was below 50%Vo<SUB>2peak</SUB>, above which the increase in Hb and decrease in HbO<SUB>2</SUB> were observed. Thus the decline in SO<SUB>2</SUB> occurred at 60%Vo<SUB>2peak</SUB> in the RF, and 70%Vo<SUB>2peak</SUB> in the VL. These results suggest that muscle deoxygenation is accelerated during exercise above a certain intensity, which is lower in the RF than in the VL, during dynamic knee-extension exercise.

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 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.