Abstract
To clarify whether the relaxation period during stretching affects the degree of elevated shear rate and the degree of reduction of arterial stiffness, we examined relaxation duration to build an adequate stretching protocol. In Experiment 1, the changes in cardiac output, the shear rate in the posterior tibial artery, and blood volume in the calf muscle were measured during recovery (0-60 s) from a single bout of one-legged passive calf stretching in 12 healthy young men. In Experiment 2, the effects of different relaxation periods (5-, 10-, 20-, and 60-s) of passive one-legged intermittent calf stretching (30-s × 6 sets) on the femoral-ankle pulse wave velocity (faPWV) as an index of peripheral arterial stiffness were identified in 17 healthy young men. As a result, the stretched leg's shear rate significantly increased from 0 to 10th s after stretching. The muscle blood volume in the stretched leg significantly reduced during stretching, and then significantly increased during the recovery period after stretching; however, cardiac output remained unchanged during stretching and recovery. Additionally, the reduction in faPWV from the pre-stretching value in the stretched leg was significantly larger in the protocol with 10-s and 20-s relaxation periods than that in the non-stretched leg, but this did not differ in the 5-s and 60-s relaxation periods. These findings suggest that the relaxation periods of intermittent static stretching that cause a high transient increase in shear rate (via reperfusion after microvascular compression by the stretched calf muscles) are effective to reduce arterial stiffness.
Highlights
Increased arterial stiffness is an independent risk factor for cardiovascular disease, a main causal factor of mortality worldwide [1,2]
Our recent study demonstrated that acute passive one-legged calf intermittent stretching (30-s × 6 sets) significantly increased shear rate as well as blood flow in the posterior tibial artery of the stretched leg during a 10-s relaxation period after stretching, when compared to that before stretching [11]. These findings suggest that intermittent calf stretching increases shear rate during the relaxation period and decreases arterial stiffness
In Exp. 1 of the present study, we revealed that the blood flow and shear rate in the posterior tibial artery increased from the baseline immediately (10 s) after 30 s of stretching
Summary
Increased arterial stiffness is an independent risk factor for cardiovascular disease, a main causal factor of mortality worldwide [1,2]. Habitual static stretching mitigates arterial stiffness [3,4,5]; it has the potential to prevent cardiovascular events. Our previous studies demonstrated that even a single bout of whole-body static stretching acutely reduced systemic arterial stiffness [6].
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