Influence of Acute Beetroot Juice Supplementation During High Intensity Fatiguing Forearm Exercise in Healthy Recreationally Active Males
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Authors
Fenuta, Alyssa Marie
Date
2024-05-17
Type
thesis
Language
eng
Keyword
acute beetroot juice supplementation , oxygen delivery , muscle blood flow , high intensity forearm exercise , critical impulse , exercise tolerance , oxygen extraction , oxygen consumption/force , incremental forearm exercise
Alternative Title
Abstract
Introduction: Exercise performance/tolerance improves with increasing oxygen delivery relative to consumption. Evidence suggests elevating blood nitrite levels may increase vasodilation and thereby oxygen delivery, and reduce the oxygen cost of exercise, improving exercise performance/tolerance.
Purpose: To determine if: 1) peak oxygen delivery:consumption is achieved during maximal effort forearm exercise identifying critical impulse, and 2) acute nitrate supplementation increases blood plasma [nitrite] improving oxygen delivery relative to consumption thereby increasing high intensity exercise performance (i.e. critical impulse, incremental exercise limit of tolerance).
Methods: Thirteen healthy males performed two fatiguing forearm handgrip exercise protocols (i.e. 10-minutes maximal effort vs. incremental exercise to limit of tolerance) while laying supine with arms outstretched 90⁰, with vs. without beetroot juice consumed 2.5 hours pre-exercise. Arterial oxygen saturation (pulse oximeter), arterial blood pressure (finger photoplethysmography), and exercising forearm blood flow (echo and Doppler ultrasound) were measured. Deep vein blood sampling assessed exercising forearm muscle metabolism and nitrate to nitrite conversion.
Results: 1) Peak forearm oxygen delivery did not differ between the two handgrip protocols. Despite achieving a lower impulse at the end of the maximal effort protocol identifying critical impulse compared to incremental exercise, the former resulted in a higher peak oxygen consumption via increased extraction indicating increased oxygen cost. 2) Acute beetroot juice supplementation resulted in repeatable increases in blood plasma [nitrite], however did not influence forearm blood flow (vasodilatory or pressor response), oxygen delivery, oxygen consumption or exercise performance/tolerance in either protocol. Beetroot juice supplementation a) reduced the oxygen cost for a given contraction impulse magnitude in the transition to critical impulse, and b) increased oxygen extraction at submaximal exercise intensities during incremental exercise.
Conclusions: Maximal effort exercise identifying critical impulse results in peak oxygen delivery:consumption and may better assess forearm aerobic capacity compared to an incremental exercise protocol. Contrary to animal work, our findings do not support the influence of beetroot juice supplementation on human muscle blood flow across the entire forearm exercise intensity continuum or handgrip exercise performance/tolerance. Additional investigation is required to explore the specific mechanism(s) potentially influencing microvascular distribution and muscle economy differences with beetroot juice supplementation.