Takuya Osada’s research while affiliated with Tokyo Medical University and other places

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Publications (4)


Figure 1. One-legged knee extensor exercise model a) <Dynamic> Isotonic muscle contraction at 60 contractions per minute performed as 0.5s-voluntary (active) muscle contraction and 0.5s-passive muscle relaxation (1s) for 5 min at 10, 20, 30 and 40 W, respectively.  
Figure 2. Simultaneous recording of blood velocity and hemodynamic parameters during exercise a) <Dynamic> Isometric muscle contractions were clearly evident in the oscillations of mean blood velocity (MBV) due to muscle contraction-relaxation cycle superimposed on the cardiac beat cycle. The MBV profile shows turbulence representing non-systole and diastole portions. b) <Static> Repeat isometric muscle contraction may indicate the clear MBV profile at each beat corresponding to the cardiac systole-diastole. The blood velocity fluctuations (coefficients of variation) were determined by each muscle contraction-relaxation cycle (● or *) as well as the cardiac beat-by-beat cycle (▲ or †). EMGs, surface electromyography; G, gap between contraction and relaxation. Figure 2a is drawn from our original unpublished data. Figure 2b is adapted from Osada et al. [15], reproduced with permission for unrestricted use from BioMed Central.  
Figure 5. Relationship between blood flow and exercise intensity a) <Dynamic> There was a close positive linear relationship between net-blood flow and workload (r = 0.991, p < 0.01). b) <Static> There was a close positive linear relationship between blood flow and %MVC during muscle relaxation (r = 0.989, p < 0.05) as well as combined muscle contraction-relaxation (r = 0.984, p < 0.05). However, blood flow during isometric muscle contraction showed no change within the target %MVC. Statics (p < 0.05 and correlation coefficient, r) -linear regression analysis. NS, not significant; %MVC, percentage of maximum voluntary contraction. The values are expressed as means ± standard error. Figure 5a adapted from Osada and Rådegran [12], reproduced with permission from Edizioni Minerva Medica. Figure 5b adapted from Osada et al. [15], reproduced with permission for unrestricted use from BioMed Central.  
Difference in muscle blood flow fluctuations between dynamic and static thigh muscle contractions: How to evaluate exercise blood flow by Doppler ultrasound
  • Article
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January 2016

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840 Reads

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8 Citations

Physical Medicine and Rehabilitation Research

Takuya Osada

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Mechanical compression during repeated sustained isometric muscle contractions and hyperemic recovery in healthy young males

December 2015

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429 Reads

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23 Citations

Journal of PHYSIOLOGICAL ANTHROPOLOGY

An elevated intramuscular pressure during a single forearm isometric muscle contraction may restrict muscle hyperemia. However, during repeated isometric exercise, it is unclear to what extent mechanical compression and muscle vasodilatation contribute to the magnitude and time course of beat-to-beat limb hemodynamics, due to alterations in leg vascular conductance (LVC). In eight healthy male subjects, the time course of both beat-to-beat leg blood flow (LBF) and LVC in the femoral artery was determined between repeated 10-s isometric thigh muscle contractions and 10-s muscle relaxation (a duty cycle of 20 s) for steady-state 120 s at five target workloads (10, 30, 50, 70, and 90 % of maximum voluntary contraction (MVC)). The ratio of restricted LBF due to mechanical compression across workloads was determined by the formula (relaxation LBF − contraction LBF)/relaxation LBF (%). The exercise protocol was performed completely by all subjects (≤50 % MVC), seven subjects (≤70 % MVC), and two subjects (≤90 % MVC). During a 10-s isometric muscle contraction, the time course in both beat-to-beat LBF and LVC displayed a fitting curve with an exponential increase (P < 0.001, r 2 ≥ 0.956) at each workload but no significant difference in mean LBF across workloads and pre-exercise. During a 10-s muscle relaxation, the time course in both beat-to-beat LBF and LVC increased as a function of workload, followed by a linear decline (P < 0.001, r 2 ≥ 0.889), that was workload-dependent, resulting in mean LBF increasing linearly across workloads (P < 0.01, r 2 = 0.984). The ratio of restricted LBF can be described as a single exponential decay with an increase in workload, which has inflection point distinctions between 30 and 50 % MVC. In a 20-s duty cycle of steady-state repeated isometric muscle contractions, the post-contraction hyperemia (magnitude of both LBF and LVC) during muscle relaxation was in proportion to the workload, which is in agreement with previous findings. Furthermore, time-dependent beat-to-beat muscle vasodilatation was seen, but not restricted, during isometric muscle contractions through all target workloads. Additionally, the relative contribution of mechanical obstruction and vasodilatation to the hyperemia observed in the repeated isometric exercise protocol was non-linear with regard to workload. In combination with repeated isometric exercise, the findings could potentially prove to be useful indicators of circulatory adjustment by mechanical compression for muscle-related disease.


Figure 4. Relationship between net-femoral arterial blood flow (FBF) and target workload during dynamic knee extensor exercise. The relationship between FBF and target workload was positive and linear at 30 cpm (r = 0.997, P < 0.01, n = 4) and 60 cpm (r = 0.999, P < 0.05, n = 3), respectively. The value of FBF for one subject was the average value of 60 samplings at each session. Furthermore, the target workload value in each individual subject was determined by averaging values of 60 samplings of the achieved workloads at each session. Both FBF and target workload were obtained from average values of all 9 subjects. Regression equations are indicated as follows: FBF (l/min) = 1.71 + 0.083 × target workload at 30 cpm (solid line): FBF (l/min) = 1.52 + 0.098 × target workload at 60 cpm (short dotted line). These data are in close agreement with the findings of Rådegran [6]: FBF (l/min) = 1.317 + 0.084 × target workload at 60 cpm, long dotted line. The difference in absolute FBF was approximately 0.5 l/min between the present FBF data and previous reports at 60 cpm by Rådegran [6]. This difference may be due to the subjects' characteristics, such as muscle strength variations and that they worked at different percentages of the maximum voluntary knee contraction force. However, the slope of the regression line in the present study is similar to previous findings. cpm, contractions per minute. Data are expressed as means  standard error. Figure adapted from Osada and Rådegran [32], reproduced with permission from John Wiley & Sons Ltd. 
Assessment of voluntary rhythmic muscle contraction-induced exercising blood flow variability measured by Doppler ultrasound

January 2013

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46 Reads

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8 Citations

Open Journal of Molecular and Integrative Physiology

Given recent technological developments, ultrasound Doppler can provide valuable measurements of blood velocity/flow in the conduit artery with high temporal resolution. In human-applied science such as exercise physiology, hemodynamic measurements in the conduit artery is commonly performed by blood flow feeding the exercising muscle, as the increase in oxygen uptake (calculated as a product of arterial blood flow to the exercising limb and the arterio-venous oxygen difference) is directly proportional to the work performed. The increased oxygen demand with physical activity is met through a central mechanism, an increase in cardiac output and blood pressure, as well as a peripheral mechanism, an increase in vascular conductance and oxygen extraction (a major part of the whole exercising muscles) from the blood. The increase in exercising muscle blood flow in relation to the target workload (quantitative response) may be one indicator in circulatory adjustment for the activity of muscle metabolism. Therefore, the determination of local blood flow dynamics (potential oxygen supply) feeding repeated (rhythmic) muscle contractions can contribute to the understanding of the factors limiting work capacity including, for instance, muscle metabolism, substance utilization and magnitude of vasodilatation in the exercising muscle. Using non-invasive measures of pulsed Doppler ultrasound, the validity of blood velocity/flow in the forearm or lower limb conduit artery feeding to the muscle has been previously demonstrated during rhythmic muscle exercise. For the evaluation of exercising blood flow, not only muscle contraction induced internal physiological variability, or fluctuations in the magnitude of blood velocity due to spontaneous muscle contraction and relaxation induced changes in force curve intensity, superimposed in cardiac beat-by-beat, but also the alterations in the blood velocity (external variability) due to a temporary sudden change in the achieved workload, compared to the target workload, should be considered. Furthermore, a small amount of inconsistency in the voluntary muscle contraction force at each kick seems to be unavoidable, and may influence exercising muscle blood flow, although subjects attempt to perform precisely similar repeated voluntary muscle contractions at target workload (muscle contraction force). This review presents the methodological considerations for the variability of exercising blood velocity/flow in the limb conduit artery during dynamic leg exercise assessed by pulsed Doppler ultrasound in relation to data previously reported in original research.


Citations (4)


... As such, this might result in greater peak pressures being applied during contractions than intended. 19 In contrast, a regulated cuff system applies a set pressure at rest prior to exercise, and then continuously and actively adjusts the applied pressure to maintain a constant applied pressure throughout the range of motion of the limb, accounting for muscular contractions under the cuff. 19,20 Therefore, the aim of this systematic review and meta-analysis was to examine (compare) the effect of regulated versus unregulated cuff pressure systems on the chronic adaptations to blood flow restriction exercise training interventions, with a specific focus on the gains in muscle strength, size and physical function as the primary outcomes of focus for blood flow restriction exercise training in both research and practice. ...

Reference:

Comparing adaptations from blood flow restriction exercise training using regulated or unregulated pressure systems: A systematic review and meta-analysis
Difference in muscle blood flow fluctuations between dynamic and static thigh muscle contractions: How to evaluate exercise blood flow by Doppler ultrasound

Physical Medicine and Rehabilitation Research

... showing that the firing rates of large motor units-which increase intramuscular pressure and peripheral vascular resistance (Osada et al., 2015)-were higher in untreated hypertensive individuals, provides a possible physiological mechanism of the exaggerated ABP response during exercise in hypertensive individuals. In other words, the hypertensive condition may modify the motor units firing pattern, which consequently leads to a higher ABP response to exercise. ...

Mechanical compression during repeated sustained isometric muscle contractions and hyperemic recovery in healthy young males

Journal of PHYSIOLOGICAL ANTHROPOLOGY

... The primary limitation of the current investigation is the absence of both an exercise intervention and central hemodynamic parameters alongside each cuff condition. Moreover, although AOP determination and blood flow parameters are most easily, accurately, and reliably measured in a resting supine position, our ability to extrapolate these data to an exercising model is limited [37,48]. We can nevertheless likely infer that the hemodynamic factors including arterial blood flow would become augmented due to enhancements in sympathetic outflow along with concomitant mean arterial pressure and CO elevations [7,49]. ...

Measurement of the exercising blood flow during rhythmical muscle contractions assessed by Doppler ultrasound: Methodological considerations

Journal of Biomedical Science and Engineering

... Finally, the anterior thigh muscles are large enough for physiological alterations to occur throughout the body, such as increases in oxygen consumption and blood lactate concentrations, further increasing the possibilities for investigating the physiology of exercise. [1][2][3]6,13,14 . Thus, future research centers can use the present study to build a DKE ergometer and investigate motor behavior or physiological aspects related to exercise. ...

Assessment of voluntary rhythmic muscle contraction-induced exercising blood flow variability measured by Doppler ultrasound

Open Journal of Molecular and Integrative Physiology