Atsuko Kagaya

Reduced exercise hyperaemia in calf muscles working at high contraction frequencies

SummaryThe effects of muscle contraction frequency on blood flow to the calf muscle (Qcalf) were studied in six female subjects, who performed dynamic plantar flexions at frequencies of 20, 40, 60, 80 and 100 contractions · min−1, in a supine position. TheQcalf measured by a mercury-in-rubber strain gauge plethysmograph, increased as contraction frequency increased and reached a peak at 60–80 contractions · min−1. After 100 plantar flexions at 60 contractions · min−1, the meanQcalf was 30.95 (SEM 4.52) ml · 100 ml−1 · min−1. At 100 contractions · min−1, however, it decreased significantly compared with that at 60 contractions · min−1 at a specified time (2 min or exhaustion) or after a fixed amount of work (100 contractions). The contraction frequency at whichQcalf reached a peak depended on the duration of exercise. The heart rate showed its highest mean value at 60 contractions · min−1 and decreased significantly at 100 contractions · min−1. The mean blood pressure was lower at 100 contractions · min−1 than at 60 contractions · min−1. The relaxation period between contractions, measured by recording the electromyogram from the gastrocnemius muscles, shortened markedly as the frequency increased; the mean value at 100 contractions · min−1 was 0.14 (SEM 0.02) s, which corresponded to 35.7% of the contraction time. This shortened relaxation period between contractions should have led to the inhibition of exercise hyperaemia at the higher contraction frequencies.

Oxygen supply-consumption balance in the thigh muscles during exhausting knee-extension exercise.

The purpose of this study was to investigate the difference in muscle oxygenation between the individual muscles involved in an exhaustive knee-extension exercise. Eight active women performed exercise by extending the knee joint from 90 degrees to 30 degrees (60 extensions min-1) at 20%, 30%, and 40% maximum voluntary contraction (MVC). Changes in oxy-(delta HbO2), deoxy-(delta Hb), and total (delta HbT) hemoglobin concentrations, and oxygen saturation (delta SO2NIRS = HbO2/HbT) in the vastus lateralis (VL) and rectus femoris (RF) muscles were measured with a spatially resolved near-infrared spectrometer (NIRS). The delta SO2NIRS in the VL and RF decreased rapidly from the pre-exercise control value (VL: 75.6 +/- 0.9%; RF: 81.6 +/- 1.6%) at the onset of exercise at three different intensities, although no significant difference in delta SO2NIRS was found between the two muscles at this time. However, the delta SO2NIRS decreased more rapidly thereafter and reached a lower value at exhaustion in the VL than in the RF. The difference in delta SO2NIRS between the VL (-10.3 +/- 1.7%) and RF (-4.0 +/- 1.0%) was significant (p < 0.05) when exercise intensity was 30% MVC. When the decreases in delta HbO2 and delta HbT (p < 0.05) were compared at different exercise intensities, the values at 30% and 40% MVC were significantly lower (delta HbO2: p < 0.01; delta HbT: p < 0.05) than those at 20% MVC in the VL, but there was no significant difference in any of the parameters in the RF, or in delta Hb in the VL. These results suggest that the muscle oxidative response to exhaustive knee-extension exercise differed between the VL and RF muscles. At exhaustion, oxygen saturation decreased to a lower level in the VL than in the RF, and an intensity-dependent difference in muscle oxygenation parameters was observed at 30% MVC in the VL but not in the RF muscles.

Central command and the increase in middle cerebral artery blood flow velocity during static arm exercise in women

We examined the role of central command in static exercise‐induced increase in middle cerebral artery mean blood flow velocity (VMCA). Eleven young female subjects performed static elbow flexion for 2 min at 30% maximal voluntary contraction without (control exercise; CONT) and with vibrations to the biceps brachii tendon (EX+VIB) in order to reduce the effort needed to maintain the set contraction intensity. The rating of perceived exertion in exercising muscle (Arm RPE) at the end of EX+VIB was lower than that of CONT (mean ±s.d.; 4.8 ± 1.1 for CONT versus 3.5 ± 1.0 for EX+VIB; P < 0.05). The increases in mean arterial pressure (36 ± 8 versus 22 ± 7%; P < 0.05), heart rate (36 ± 16 versus 21 ± 7%; P < 0.05) and cardiac output (56 ± 26 versus 39 ± 14%; P < 0.05) during EX+VIB were also lower than those during CONT. Similarly, the increase in the VMCA during EX+VIB was lower than that during CONT (29 ± 5 versus 17 ± 14%; P < 0.05). These results suggest that the influence of central command contributes to cerebral blood flow regulation during static exercise and the decrease in VMCA is likely to be caused by attenuated brain activation in the central command network and/or by the reduction in cardiac output.

Exhausting handgrip exercise reduces the blood flow in the active calf muscle exercising at low intensity

The calf and forearm blood flows (Qcalf and Qforearm respectively), blood pressure, heart rate and oxygen uptake of six men and women were studied during combined leg and handgrip exercise to determine whether a reduction of exercise-induced hyperaemia would occur in the active leg when exhausting rhythmic handgrip exercise at 50% maximal voluntary contraction (MVC) was superimposed upon rhythmic plantar flexion lasting for 10 min at 10% MVC (P10) prior to this combined exercise. The Qcalf and Qforearm were measured by venous occlusion plethysmography during 5-s rests interposed during every minute of P10 exercise and immediately after combined exercise. The muscle sympathetic nerve activity (MSNA) changes were also recorded during leg exercise alone and combined exercise. During plantar flexion performed 60 times · min−1 with a load equal to 10% MVC (P10), Qcalf was maintained at a constant level, which was significantly higher than the resting value (P < 0.001). When rhythmic handgrip contraction at 50% MVC (H50) and P10 were performed simultaneously, the combined exercise was concluded due to forearm exhaustion after a mean of 51.2 (SEM 5.5) s. At exhaustion, Qcalf had decreased significantly from 20.6 (SEM 3.0) ml · 100 ml−1 · min−1 (10th min during P10 exercise) to 15.3 (SEM) ml · 100 ml−1 · min−1 (P = 0.001), whereas Qforearm had increased significantly (0.001 < P < 0.01) from 8.6 (SEM 1.9) ml · 100 ml−1 · min−1 (10th min of P10 exercise) to 26.2 (SEM 3.2) ml · 100 ml−1 · min−1. The mean blood pressure remained at an almost constant level during the 3rd to 10th min of P10 exercise and increased markedly when H50 was added. The calf vascular conductance during combined exercise decreased significantly (0.001 < P < 0.01) compared with that at the 10th min of P10 alone. Although the MSNA (expressed as burst rate) remained unchanged during P10 exercise for 10 min, it increased markedly when exhausting H50 and P10 exercise were performed simultaneously. These findings indicated that superimposition of exhausting handgrip exercise at 50% MVC caused a vasoconstriction in the exercising calf due to increased MSNA, which counteracted the vasodilatation in this active muscle.

Detection of Oxygen Consumption in Different Forearm Muscles During Handgrip Exercise by Spatially Resolved Nir Spectroscopy

Muscle O2 kinetics during exercise in humans have been estimated by measuring blood flow, and arterial and venous O2 contents. To date, plethysmography and the ther-modilution method have been used for blood flow measurement. The blood flow values estimated by these methods have been considered to represent the average value for several working muscles. To estimate the venous O2 content, blood samples have been collected from the antecubital vein during handgrip exercise (Joyner et al.1992, Hartling et al. 1989) and from the femoral vein during \eg exercise (Costes et al. 1996, Richardson et al. 1995, Vollestad et al. 1990). Since these veins are relatively large, the venous O2 content estimated from the blood collected from them has also been considered to represent the average for several working muscles. Thus, in humans, O2 kinetics during exercise have been estimated as the average values for several working muscles, and differences in O2 kinetics between individual working muscles which contribute to the exercise have not been detected. The recent development of near-infrared (NIR) spectroscopy makes it possible to estimate changes in O2 levels in small blood vessels, capillaries, and intracellular O2 uptake sites (Mancini et al. 1994). The estimation of changes in O2 supply and consumption in muscle tissue has been achieved using the venous occlusion technique (Homma et al. 1996a), while tissue O2 saturation has been demonstrated using spatially resolved NIR spectroscopy (Farell et al. 1992, Tsunazawa et al. 1996). The aim of this study was to investigate differences in the O2 kinetics of two individual muscles, both working during handgrip exercise of various intensities, using spatially resolved NIR spectroscopy.

Blood flow and arterial vessel diameter change during graded handgrip exercise in dominant and non-dominant forearms of tennis players

The training effect on exercise-induced maximal blood flow remains unclear. The purpose of this study was to clarify the difference of exercise-induced blood flow, blood flow velocity and vessel diameter of brachial artery in dominant and non-dominant forearms of tennis players during graded hand-grip exercise. Ten female tennis players aged 20.1 +/- 0.1 years. (mean +/- SD) performed 30-s static handgrip exercise in the supine position with either the dominant or non-dominant hand by increasing load at 30-s intervals until exhaustion. Brachial arterial blood flow velocity (Doppler ultrasound method) did not differ between both limbs, whereas the vessel diameter (2-D method) was significantly larger in the dominant limb during diastole both at baseline (p < 0.01) and after exercise (p < 0.05), but no difference was found during systole. As a result, the blood flow was significantly higher (p < 0.05) in the dominant limb during post-exercise condition. Muscle thickness of the forearm muscles and maximal handgrip strength were significantly higher in the dominant limb. Thus, the effect of training on exercise-induced blood flow specific to the dominant limb was confirmed during post-exercise due to the enlarged vessel diameter during diastole of cardiac cycle. The dimensional change in the vasculature specific to the dominant side will be included in the training effects associated with the dimensional muscular changes in the dominant forearm.

Relative contraction force producing a reduction in calf blood flow by superimposing forearm exercise on lower leg exercise

SummaryThe relative contraction force producing a reduction in exercise hyperaemia was studied by superimposing handgrip contraction at different intensities on plantar flexion of low intensity. Ten active women served as subjects. Blood flow to the forearm (

Differential cardiorespiratory response to combined exercise with different combinations of forearm and calf exercise

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