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  • Title: Cardiovascular responses to static and dynamic contraction during comparable workloads in humans.
    Author: Stebbins CL, Walser B, Jafarzadeh M.
    Journal: Am J Physiol Regul Integr Comp Physiol; 2002 Sep; 283(3):R568-75. PubMed ID: 12184989.
    Abstract:
    Previous studies suggest that the blood pressure response to static contraction is greater than that caused by dynamic exercise. In anesthetized cats, however, pressor responses to electrically induced static and dynamic contraction of the same muscle group are similar during equivalent workloads and peak tension development [i.e., similar tension-time index (TTI)]. To determine if the same relationship exists in humans, where contraction is voluntary and central command is present, dynamic (180 s; 1/s) and static (90 s) contractions at 30% of maximal voluntary contraction (MVC) were performed. Dynamic contraction also was repeated at the same TTI for 90 s at 60% MVC. Mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), MAP during postexercise arterial occlusion (an index of the metaboreceptor-induced activation of the exercise pressor reflex), and relative perceived exertion (RPE) (an index of central command) were assessed. No differences in these variables were found between static and dynamic contraction at a tension of 30% MVC. During dynamic contraction at 60% MVC, changes in MAP (16 +/- 3 vs. 19 +/- 4 mmHg) and absolute HR (92 +/- 6 vs. 69 +/- 5 beats/min), CO (7.9 +/- 0.4 vs. 6.3 +/- 0.3 l/min), RPE (16 +/- 1 vs. 13 +/- 1), and MAP during postexercise arterial occlusion (115 +/- 3 vs. 100 +/- 4 mmHg) were greater than during static contraction (P < 0.05). Thus increases in MAP and HR, activation of central command, and muscle metabolite-induced stimulation of the exercise pressor reflex during static and dynamic contraction in humans seem to be similar when peak tension and TTI are equal. Augmented responses to dynamic contraction at 60% MVC are likely related to greater activation of these two mechanisms.
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