Muscle Oxygenation Level Might Trigger the Regulation of Capillary Venous Blood Filling during Fatiguing Isometric Muscle Actions

Figures

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  Figure 1. Measurement position and set up during a holding isometric muscle action (HIMA) (a), reprinted from Dech et al. (2020) [6] with permission, and during a pulling isometric muscle action (PIMA) (b).

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  Figure 2. Curve examples of the capillary venous oxygen saturation of hemoglobin (SvO2; red) and the relative hemoglobin amount (rHb, blue) in type I (a) with left arm and in type II (b) with the right arm of the same male left-hander (26 yrs, 1.85 m, 86 kg) during two fatiguing pulling isometric muscle actions at 60% of the MVIC of the biceps brachii muscle. Start and stop of loading are indicated by vertical lines. The first local minimum (1st Min.) was set exemplarily in (a) and the first local maximum (1st Max.) as well as reversal points (RP1, RP2) in (b). All curves were smoothed (moving average, maximal smoothing width: 50).

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  Figure 3. Capillary venous oxygen saturation of hemoglobin (SvO2 in %) of 36 fatiguing measurements of twelve subjects. Type I minimum values (red crosses, n = 10) sorted by oxygenation level. Type II SvO2 values at the first reversal points of the relative hemoglobin amount (RP1, n = 26, black, sorted by oxygenation level) and respective SvO2 values at RP2 (grey) as well as minimum values (red crosses). In some measurements, RP1 and RP2 are nearly identical (only grey dots). The horizontal lines express the arithmetic means of SvO2 values at RP1 (black, hidden) and RP2 (grey) of all 26 type II measurements. Dashed lines show the respective upper and lower 1.96-fold standard deviations.

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  Figure 4. Capillary venous oxygen saturation of hemoglobin (SvO2 in %) of 24 MVIC-tests of six subjects. Type I minimum values (red crosses, n = 15) sorted by oxygenation level. Type II SvO2 values at the first reversal points of the relative hemoglobin amount (RP1, n = 9, black, sorted by oxygenation level) and respective SvO2 values at RP2 (grey) as well as minimum values (red crosses). The horizontal lines express the arithmetic means of SvO2 values at RP1 (black) and RP2 (grey) of all nine type II measurements. Dashed lines show the respective upper and lower 1.96-fold standard deviations.

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  Figure 5. Cross-section of a striated human muscle. Capillaries are located in the endomysium where several muscle fibers adjoin. Cave: Nuclei (blue) are easily confused with capillaries (modified according to Sorenson and Brelje, University of Minnesota, Minneapolis, MN, USA, with kind permission [65]).