January 2016
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840 Reads
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8 Citations
Physical Medicine and Rehabilitation Research
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January 2016
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840 Reads
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8 Citations
Physical Medicine and Rehabilitation Research
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.
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.
January 2012
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50 Reads
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9 Citations
Journal of Biomedical Science and Engineering
... 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. ...
January 2016
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. ...
December 2015
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]. ...
January 2012
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. ...
January 2013
Open Journal of Molecular and Integrative Physiology