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

Silas Dech,Frank N Bittmann,Laura V Schaefer

doi:10.3390/diagnostics11111973

Abstract

The regulation of oxygen and blood supply during isometric muscle actions is still unclear. Recently, two behavioral types of oxygen saturation (SvO2) and relative hemoglobin amount (rHb) in venous microvessels were described during a fatiguing holding isometric muscle action (HIMA) (type I: nearly parallel behavior of SvO2 and rHb; type II: partly inverse behavior). The study aimed to ascertain an explanation of these two regulative behaviors. Twelve subjects performed one fatiguing HIMA trial with each arm by weight holding at 60% of the maximal voluntary isometric contraction (MVIC) in a 90° elbow flexion. Six subjects additionally executed one fatiguing PIMA trial by pulling on an immovable resistance with 60% of the MVIC with each side and same position. Both regulative types mentioned were found during HIMA (I: n = 7, II: n = 17) and PIMA (I: n = 3, II: n = 9). During the fatiguing measurements, rHb decreased initially and started to increase in type II at an average SvO2-level of 58.75 ± 2.14%. In type I, SvO2 never reached that specific value during loading. This might indicate the existence of a threshold around 59% which seems to trigger the increase in rHb and could explain the two behavioral types. An approach is discussed to meet the apparent incompatibility of an increased capillary blood filling (rHb) despite high intramuscular pressures which were found by other research groups during isometric muscle actions.

Highlights

During exercise, the demand for oxygen, nutrients and, blood increases in the muscular capillary system to transfer chemical energy into mechanical energy
It was found that the blood filling can increase after a previous decrease during isometric muscle actions (IMAs) at intensities of 60% and even of 100% of the maximal voluntary isometric contraction (MVIC)
The method used does not allow for direct conclusions on capillary blood flow, but indirect conclusions by regarding relative hemoglobin amount (rHb) and SvO2 behaviors can be drawn

Summary

Introduction

The demand for oxygen, nutrients and, blood increases in the muscular capillary system to transfer chemical energy into mechanical energy. The oxygen saturation showed an immediate decrease at the onset of loading [6,7,8,9,10] or short increase [11], followed by a leveling off into a steady state until fatigue [6,7,8,9,10,11]. These studies revealed that a homeostasis of oxygen delivery and consumption during IMAs is basically possible. Steady states were found in studies with limited loading durations [19,20,21]

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