The influence of absolute intensity on cardiovascular responses to exercise

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Lee, Jordan

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University of Guelph

Abstract

Background: Blood pressure responses to dynamic and static resistance exercise are thought to be determined by relative exercise intensity, rather than the absolute force being exerted. This paradigm was derived from studies using small, primarily male, samples, and often during performance of large muscle mass, maximal intensity exercise. In contrast, pre-menopausal females have smaller cardiovascular responses to small muscle mass relative intensity exercise compared to males, and accounting for strength differences abolishes these differences. Within sex, maximal strength is positively associated with blood pressure responsiveness. Purpose: This thesis studied sex differences in muscle strength as a model to explore the role of absolute intensity in determining blood pressure responses to large muscle mass exercise, as well as the mechanisms involved. The overarching aim was to examine whether absolute exercise intensity contributes to variability in blood pressure responsiveness at low- to moderate-relative exercise intensities.
Methods: Continuous, beat-by-beat hemodynamics were assessed during studies involving static and dynamic exercise in males and females. Muscle oxygenation and electromyography were assessed to provide insight into peripheral and central mechanisms contributing to the influence of absolute intensity. Results: Females had lower blood pressure responses to large muscle mass static and dynamic exercise, whereas controlling for absolute intensity accounted for these differences. Higher muscle strength influenced blood pressure responses by increasing muscle metaboreflex activation during static exercise, and through increased activation of central command and the muscle mechanoreflex. When muscle strength was acutely reduced following eccentric exercise, blood pressure responses to metaboreflex activation were also reduced. Conclusions: These findings demonstrate that absolute intensity contributes to the magnitude of the blood pressure response to exercise at a given relative intensity. Large differences in maximal strength can drive group differences in blood pressure responses, highlighting the need to account for absolute intensity when studying exercise blood pressures.

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Blood pressure, exercise, sex differences, autonomic nervous system

Citation

Lee, J. B., Lutz, W., Omazic, L. J., Jordan, M. A., Cacoilo, J., Garland, M., Power, G. A., & Millar, P. J. (2021). Blood Pressure Responses to Static and Dynamic Knee Extensor Exercise between Sexes: Role of Absolute Contraction Intensity. Medicine and Science in Sports and Exercise, 53(9), 1958�??1968. https://doi.org/10.1249/MSS.0000000000002648
Lee, J. B., Notay, K., Seed, J. D., Nardone, M., Omazic, L. J., & Millar, P. J. (2021). Sex Differences in Muscle Metaboreflex Activation after Static Handgrip Exercise. Medicine and Science in Sports and Exercise, 53(12), 2596�??2604. https://doi.org/10.1249/MSS.0000000000002747