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Near-infrared spectroscopy estimation of combined skeletal muscle oxidative capacity and O 2 diffusion capacity in humans
The final steps of the O cascade during exercise depend on the product of the microvascular-to-intramyocyte difference and muscle O diffusing capacity ( ). Non-invasive methods to determine in humans are currently unavailable. Muscle oxygen uptake (m ) recovery rate constant (k), measured by near-in...
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Published in: | The Journal of physiology 2022-09, Vol.600 (18), p.4153-4168 |
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Main Authors: | , , , , , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | The final steps of the O
cascade during exercise depend on the product of the microvascular-to-intramyocyte
difference and muscle O
diffusing capacity (
). Non-invasive methods to determine
in humans are currently unavailable. Muscle oxygen uptake (m
) recovery rate constant (k), measured by near-infrared spectroscopy (NIRS) using intermittent arterial occlusions, is associated with muscle oxidative capacity in vivo. We reasoned that k would be limited by
when muscle oxygenation is low (k
), and hypothesized that: (i) k in well oxygenated muscle (k
) is associated with maximal O
flux in fibre bundles; and (ii) ∆k (k
- k
) is associated with capillary density (CD). Vastus lateralis k was measured in 12 participants using NIRS after moderate exercise. The timing and duration of arterial occlusions were manipulated to maintain tissue saturation index within a 10% range either below (LOW) or above (HIGH) half-maximal desaturation, assessed during sustained arterial occlusion. Maximal O
flux in phosphorylating state was 37.7 ± 10.6 pmol s
mg
(∼5.8 ml min
100 g
). CD ranged 348 to 586 mm
. k
was greater than k
(3.15 ± 0.45 vs. 1.56 ± 0.79 min
, P < 0.001). Maximal O
flux was correlated with k
(r = 0.80, P = 0.002) but not k
(r = -0.10, P = 0.755). Δk ranged -0.26 to -2.55 min
, and correlated with CD (r = -0.68, P = 0.015). m
k reflects muscle oxidative capacity only in well oxygenated muscle. ∆k, the difference in k between well and poorly oxygenated muscle, was associated with CD, a mediator of
. Assessment of muscle k and ∆k using NIRS provides a non-invasive window on muscle oxidative and O
diffusing capacity. KEY POINTS: We determined post-exercise recovery kinetics of quadriceps muscle oxygen uptake (m
) measured by near-infrared spectroscopy (NIRS) in humans under conditions of both non-limiting (HIGH) and limiting (LOW) O
availability, for comparison with biopsy variables. The m
recovery rate constant in HIGH O
availability was hypothesized to reflect muscle oxidative capacity (k
) and the difference in k between HIGH and LOW O
availability (∆k) was hypothesized to reflect muscle O
diffusing capacity. k
was correlated with phosphorylating oxidative capacity of permeabilized muscle fibre bundles (r = 0.80). ∆k was negatively correlated with capillary density (r = -0.68) of biopsy samples. NIRS provides non-invasive means of assessing both muscle oxidative and oxygen diffusing capacity in vivo. |
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ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/JP283267 |