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Thesis Format

Integrated Article

Degree

Master of Science

Program

Kinesiology

Supervisor

Kowalchuk, John M.

Abstract

The current study assessed alterations to the linear V̇O2p slow component (V̇O2p SC)-muscle fatigue development relationship using dietary nitrate (NO3- ) supplementation during very heavy (VH)-intensity constant-work rate cycling exercise. Using a double- blind, block-randomised, crossover design, 8 healthy men (age, 24±2 yr [mean±SD]; V̇O2p-max, 43.8±6.0 mL/kg/min) consumed NO3- -rich (BRJ) or -depleted (PLAC) beetroot juice daily for 20 d. Participants completed pre/post-condition incremental leg cycling V̇O2p-max and 3-min “sprint” verification exercises. An initial 5 d loading phase was followed, on alternate days, by single trials of VH- or moderate-intensity exercise at select time points with a 14 d washout period separating conditions. Muscle fatigue was assessed pre/post- exercise by electrically stimulated quadriceps muscle torque production. NO3- supplementation had no effect on the development of the V̇O2p SC amplitude or muscle fatigue or the linear relationship between the two variables (slope = 6.85 (BRJ) vs. 8.34 (PLAC) (mL/min)/(10/50 Hz ratio; P = 0.628).

Summary for Lay Audience

When exercising at a constant work rate (WR) the rate of oxygen (O 2 ) consumption measured at the lungs (V̇O2p) is also constant. When the WR is increased to a level below a threshold exercise physiologists term “lactate threshold” (θL), V̇O2p increases to a new “steady state” within 2-3 minutes. If the increased WR is beyond θL, the increase in V̇O2p is higher than that which would be predicted by the sub-θL linear relationship between the increase in WR and V̇O2p. This extraneous V̇O2p is termed the “V̇O2 slow component” (V̇O2p SC), and a steady state is reached over a longer time period (approximately 10 minutes). When exercising above a higher threshold termed “critical power” (CP), a V̇O2p steady state is never reached. Instead, V̇O2p continues to increase until the muscle’s ability to utilize O2 is maximised (V̇O2p-max) or the participant discontinues exercise. While the determinants of the extraneous V̇O2p is unknown, it has been linked to the progressive development of muscle fatigue. Muscle fatigue can be inferred through the decrease in muscle torque production induced by involuntary electrical stimulation of the muscle. Nitrate (NO3-), a molecular compound commonly found in leafy green foods, has been implicated in lowering the V̇O2p at given time points in some studies employing constant-WR exercise above CP when consumed as a concentrated form of beetroot juice. Additionally, studies have shown an increase in the muscle’s ability to contract with NO3- supplementation. Considering these effects, the current study examined how NO3- supplementation might influence the linear relationship between the increase in the V̇O2p SC development and muscle fatigue, thereby furthering our understanding of muscle function. Eight young, healthy men were randomly placed into nitrate and placebo supplementation groups. They completed stationary supra-CP WR cycling exercises of various duration whilst measuring V̇O2p SC. The participants also completed muscle fatigue testing prior to and following each test. At the end of each condition, the participants switched conditions following a 14 d period without any supplementation and repeated the protocol. NO3- supplementation did not alter the relationship between the development of the V̇O2p SC development and muscle fatigue.

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