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Limb blood flow and muscle oxygenation responses to rhythmic exercise below and above critical force
Author(s) -
Hammer Shane M.,
Alexander Andrew M.,
Didier Kaylin D.,
Huckaby Lillie M.,
Barstow Thomas J.
Publication year - 2020
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2020.34.s1.04230
Subject(s) - isometric exercise , hematocrit , oxygenation , blood flow , heme , chemistry , intensity (physics) , microcirculation , cycle ergometer , cardiology , medicine , nuclear magnetic resonance , heart rate , biochemistry , blood pressure , physics , quantum mechanics , enzyme
This study aimed to determine brachial artery blood flow (Q̇ BA ) and microvascular oxygen delivery responses to rhythmic exercise above and below critical force (CF; the isometric analog of critical power). We hypothesized that Q̇ BA , deoxygenated‐heme (deoxy‐[heme]; an estimate of microvascular fractional oxygen extraction), and total‐heme concentrations (total‐[heme]; an estimate of changes in microvascular hematocrit) would demonstrate physiological maximums above CF despite increases in exercise intensity. 13 healthy subjects performed 1) a 5‐min rhythmic isometric‐handgrip maximal‐effort test (MET) to determine CF and 2) constant target‐force tests above (severe‐intensity; S1 and S2) and below (heavy‐intensity; H1 and H2) CF. CF was 189.3 ± 16.7 N (29.7 ± 1.6 %MVC). At end‐exercise, Q̇ BA was greater during S1 (418 ± 147 mL/min) and S2 (403 ± 137 mL/min) than during H1 (287 ± 97 mL/min) and H2 (340 ± 116 mL/min; p < 0.05) but was not different between S1 and S2. Further, Q̇ BA for S1 and S2 were not significantly different from the Q̇ BA estimated for CF (392 ± 37 mL/min). At end‐exercise, deoxy‐[heme] was not different between S1 (150 ± 50 μM) and S2 (155 ± 57 μM), but was greater during S1 and S2 than during H1 (101 ± 24 μM) and H2 (111 ± 21 μM; p < 0.05). Total‐[heme] was not different between S1 (404 ± 58 μM) and S2 (397 ± 73 μM), but was greater during S1 and S2 than H1 (352 ± 58 μM; p < 0.01) but not H2 (371 ± 57 μM). These data suggest limb blood flow limitations and maximal levels of muscle microvascular oxygen delivery and extraction during exercise above, but not below, CF.End‐exercise brachial artery blood flow (Q̇ BA ) values. Q̇ BA at end‐exercise below (● H1 and ○ H2) and above (▼ S1 and Δ S2) critical force (CF), and Q̇ BA predicted at CF by linear regression (♦). * Significantly greater than Q̇ BA at end‐exercise during H1 (p < 0.05). ** Significantly greater than Q̇ BA at end‐exercise during H2 (p < 0.05). Note no differences among end‐exercise Q̇ BA values at (estimated) and above CF, suggesting a maximal response in the severe‐intensity domain.Frequency‐domain near‐infrared spectroscopy (FD‐NIRS) measurements of muscle oxygenation during exercise below (● H1 and ○ H2) and above (▼ S1 and Δ S2) critical force (CF). Dashed lines indicate average endexercise values of respective FD‐NIRS signals during the maximal‐effort test (MET). * Significantly different from end‐exercise during H1 and H2 (p < 0.05). ** Significantly greater than total‐[heme] at end‐exercise during H2 (p < 0.05).