The rate of peripheral circulatory adjustment at the onset of exercise was studied in six active women aged 2022 yrs. Five bouts of exercise with different duration of 15, 30, 60, 120 and 180 s were performed on a level treadmill at an intensity of 70% Vo₂max. Calf blood flow was measured with a mercury-in-rubber strain gauge plethysmograph immediately after cessation of each bout of exercise. Heart rate and Vo₂ were measured during running.
Calf blood flow after 15-s exercise increased to 25.98±3.51 ml/100 ml/min (mean±SD), which corresponded to 70% of the mean calf blood flow (32.80 ml/100 ml/min) immediately after 180-s exercise. The relative increases in calf blood flow after 15- and 30-s exercise were significantly higher than those of heart rate. The Vo₂ after exercise of identical duration showed a smaller percentage increase in comparison with heart rate.
The increase of calf blood flow or heart rate was fitted best by a monoexponential equation, Yt=C-ae^-kt, where Yt is the response at time t (s) expressed as a percentage of the value at 180-s exercise, C is 100 in the present study, and k is a rate constant. The rate constant k in the equations ranged from 0.025 to 0.179 for blood flow and 0.025 to 0.036 for the heart rate. The calculated half-times (t1/2) for the increase in blood flow averaged 12.85 s, ranging from 5.6 to 20.0 s. This was significantly (p<0.05) shorter than HRt 1/2, which averaged 21.7 s.
The present study therefore showed that the adjustment of the peripheral circulatory system at the commencement of treadmill runnning at an intensity of 70% Vo₂max preceded the central circulatory adjustment.

This review describes age-related changes in muscle work capacity and muscle blood flow as an indicator of oxygen transport capacity. Maximal endurance time, measured using a given relative load, did not differ between younger and older people ; and the strength decline ratio, as a percent of maximal voluntary contraction, remained constant across the middle- and old age groups, or slightly increased with age. A likely explanation would be the agerelated modification of muscle fiber composition. In contrast, the recently proposed submaximal test indicated that the breaking point of blood pressure regulation (BP_critical), during progressively increasing exercise, significantly decreased in the elderly in their 70 s. Concerning muscle blood flow in the elderly, the results are inconsistent. Some studies indicated the muscle blood flow during leg or handgrip exercise can be preserved in the elderly ; other studies reported it decreases in older people both at baseline and during exercise. Longitudinal studies on elderly people show that training can reverse age-related peripheral circulatory changes in healthy older people. In addition, daily physical activity is related to muscle work capacity and gradually decreases with age. Thus, further studies are needed concerning whether the decline of muscle work capacity or the reduction of muscle blood flow with age is due to aging or inactivity in older people.

The purpose of this study was to determine the difference in vascular conductance changes in brachial and femoral artery (BVC, FVC) of non-exercising limbs during handgrip exercise at different intensities. Six subjects performed rhythmic handgrip exercise, which consisted of 2-second contraction and 2-second relaxation at the intensities of 15%, 30%, and 45% of maximal voluntary contraction (MVC). Brachial and femoral artery blood flow (Doppler ultrasound method) of non-exercising limbs, blood pressure, and heart rate were measured. The BVC during exercise at lower intensities (15% and 30%MVC) and FVC during exercise at any of three intensities did not change significantly. However, BVC significantly decreased at 45%MVC when the exercise was continued to longer than 60% of maximal endurance time (P<0.05). These results suggest that FVC of the non-exercising limb dose not change during handgrip exercise at the intensity lower than 45%MVC, but BVC of the non-exercising limb change during handgrip exercise depending on the exercise intensity and duration.

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 (Vo₂) was measured by the 10-s mixing chamber method. Changes in oxygenated hemoglobin (HbO₂), 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 (SO₂) was calculated as the HbO₂ 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_2peak. However, the HbO₂ and Hb remained unchanged when exercise intensity was below 50%Vo_2peak, above which the increase in Hb and decrease in HbO₂ were observed. Thus the decline in SO₂ occurred at 60%Vo_2peak in the RF, and 70%Vo_2peak 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.

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_sys) was calculated as the product of SV and HR. Blood flow to the forearm (Q_foream, ) was measured by venous occlusion plethysmography. Q_sys, 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_forearm, was significantly lower during BHG than RHG and LHG exercise (p<0.05) .
These results suggest that Q_sys, does not differ between unilateral and bilateral handgrip exercise, despite the increase in active muscle mass. The unchanged Q_sys could be explained by the Q_forearm reduction during BHG. The Q_forearm was lower during BHG than during the unilateral handgrip exercises, possibly due to vasoconstriction induced by BHG exercise.

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.

The purpose of this study was to elucidate how long it takes to reach peak blood flow after muscle contractions in consideration of the cardiac cycle. Seven healthy female subjects performed two successive dynamic plantar flexions of 1-s duration at 30, 50 and 70% of maximal voluntary contraction (MVC). Based upon the blood flow response after a single contraction, we set up intervals during two successive contractions each corresponding to 10% (10 I), 30% (30 I) and 50% (50 I) of the time required to reach peak blood flow. Upon cessation of contraction, the popliteal artery blood flow (Qpa) increased progressive, beat-by-beat increase and peaked by the 5^th cardiac cycle, for all conditions. The highest peak blood flow among the cardiac cycle was at 3^rd cycle in overall data. Peak Qpa values reached after exercise did not differ among intervals, whereas peak Qpa value attained after exercise was significantly greater in 50 and 70%MVC than 30%MVC (p<0.05). The result indicates that the augmentation of the Qpa after exercise with short duration differed with the exercise intensity but the timing for reaching peak post-exercise value did not differ in terms of the number of cardiac cycles.

The purpose of this study was to clarify the relationship between left ventricular muscle mass, skeletal muscle volume and vessel structures in elderly women (n=15, 76.0±5.4 years). We measured the thigh muscle thickness, and brachial and common carotid arterial diameter using B-mode ultrasound method. Posterior wall thickness, interventricular septal thickness, left ventricular end-diastolic internal diameter, and aorta artery were measured by B-mode echocardiography. No significant relationship was obtained between brachial and common carotid arterial diameters, and aortic diameter. On the other hand, significant correlation coefficients were obtained between cardiac muscle thickness and thigh muscle thickness (r=0.674, p<0.01). A significant correlation coefficient was also obtained between the estimated skeletal muscle volume and left ventricular mass [LVmass](r=0.542, p<0.05). The slope of regression equation between estimated thigh muscle volume and LVmass in elderly women in this study was (y=0.11x+75.65) steeper than in children (y=0.06x+14.02) reported previously. These results indicate that the ventricular muscle (LVmass) is closely related to the skeletal muscle volume in ordinary elderly women and skeletal muscle mass at a given LVmass is smaller in elderly women than children.

The purpose of this study was to confirm the causal structure model of muscle, motor and living functions utilizing structural equation modeling (SEM) . As subjects, 103 community-dwelling older men and women, aged 65.7±6.9years of age, participated in the study to measure muscle cross-sectional area, maximum voluntary contractions, muscle power, 4 physical performance tests, and 16 questionnaires regarding ability of activities of daily living. The causal structure model of muscle, motor and living functions was hypothesized to be a hierarchical causal structure. The causal structure model of muscle function was hypothesized to be a hierarchical causal structure consisting of 3 sub-domains of muscle mass, muscle strength, and muscle power. Data analysis procedures were as follows : a) testing of construct validity of muscle function variables using confirmatory factor analysis (CFA) in SEM ; b) testing of causal structure using SEM ; c) testing of factor invariance using multi-group analysis for gender. The highest goodness of fit indices was obtained in the causal structure model of muscle, motor and living functions (NFI= .928, CFI= .978, RMSEA =.061) . The causal coefficient of muscle function to motor function was .98 (p<.05), followed by.34 for motor function to living function. From the results of multi-group analysis, the measurement invariance model indicated the highest goodness of fit indices (TLI=.968, CFI .977) . It was concluded that the hierarchical causal relation was among muscle, motor and living functions, and in which muscle function was consisted of 3 sub-domains.