In the last decade the study of the human brain and muscle energetics underwent a radical change, thanks to the progressive introduction of noninvasive techniques, including near-infrared (NIR) spectroscopy (NIRS). This review summarizes the most recent literature about the principles, techniques, advantages, limitations, and applications of NIRS in exercise physiology and neuroscience. The main NIRS instrumentations and measurable parameters will be reported. NIR light (700-1000 m) penetrates superficial layers (skin, subcutaneous fat, skull, etc.) and is either absorbed by chromophores (oxy- and deoxyhemoglobin and myoglobin) or scattered within the tissue. NIRS is a noninvasive and relatively low-cost optical technique that is becoming a widely used instrument for measuring tissue O2 saturation, changes in hemoglobin volume and, indirectly, brain/muscle blood flow and muscle O2 consumption. Tissue O2 saturation represents a dynamic balance between O2 supply and O2 consumption in the small vessels such as the capillary, arteriolar, and venular bed. The possibility of measuring the cortical activation in response to different stimuli, and the changes in the cortical cytochrome oxidase redox state upon O2 delivery changes, will also be mentioned.

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Principles, techniques, and limitations of near infrared spectroscopy.

Near-infrared spectroscopy (NIRS) was initiated in 1977 by Jobsis as a simple, noninvasive method for measuring the presence of oxygen in muscle and other tissues in vivo. This review honoring Jobsis highlights the progress that has been made in developing and adapting NIRS and NIR imaging (NIRI) technologies for evaluating skeletal muscle O(2) dynamics and oxidative energy metabolism. Development of NIRS/NIRI technologies has included novel approaches to quantification of the signal, as well as the addition of multiple source detector pairs for imaging. Adaptation of NIRS technology has focused on the validity and reliability of NIRS measurements. NIRS measurements have been extended to resting, ischemic, localized exercise, and whole body exercise conditions. In addition, NIRS technology has been applied to the study of a number of chronic health conditions, including patients with chronic heart failure, peripheral vascular disease, chronic obstructive pulmonary disease, varying muscle diseases, spinal cord injury, and renal failure. As NIRS technology continues to evolve, the study of skeletal muscle function with NIRS first illuminated by Jobsis continues to be bright.

https://www.spiedigitallibrary.org/journals/Journal-of-Biomedical-Optics/volume-12/issue-06/062105/Near-infrared-spectroscopy-imaging-for-monitoring-muscle-oxygenation-and-oxidative/10.1117/1.2805437.pdf

Near-infrared spectroscopy/imaging for monitoring muscle oxygenation and oxidative metabolism in healthy and diseased humans

Previous studies have revealed a novel interaction between deoxyhemoglobin and nitrite to generate nitric oxide (NO) in blood It has been proposed that nitrite acts as an endocrine reservoir of NO

Deoxymyoglobin is a Nitrite Reductase That Generates Nitric Oxide and Regulates Mitochondrial Respiration

The aim of this study was to investigate local muscle O(2) consumption (muscV(O(2))) and forearm blood flow (FBF) in resting and exercising muscle by use of near-infrared spectroscopy (NIRS) and to compare the results with the global muscV(O(2)) and FBF derived from the well-established Fick method and plethysmography. muscV(O(2)) was derived from 1) NIRS using venous occlusion, 2) NIRS using arterial occlusion, and 3) the Fick method [muscV(O(2(Fick)))]. FBF was derived from 1) NIRS and 2) strain-gauge plethysmography. Twenty-six healthy subjects were tested at rest and during sustained isometric handgrip exercise. Local variations were investigated with two independent and simultaneously operating NIRS systems at two different muscles and two measurement depths. muscV(O(2)) increased more than fivefold in the active flexor digitorum superficialis muscle, and it increased 1.6 times in the brachioradialis muscle. The average increase in muscV(O(2(Fick))) was twofold. FBF increased 1.4 times independent of the muscle or the method. It is concluded that NIRS is an appropriate tool to provide information about local muscV(O(2)) and local FBF because both place and depth of the NIRS measurements reveal local differences that are not detectable by the more established, but also more global, Fick method.

https://www.physiology.org/doi/pdf/10.1152/jappl.2001.90.2.511

Performance of near-infrared spectroscopy in measuring local O(2) consumption and blood flow in skeletal muscle.

The activity patterns of many sports (e.g. badminton, basketball, soccer and squash) are intermittent in nature, consisting of repeated bouts of brief (≤6-second) maximal/near-maximal work interspersed with relatively short (≤60-second) moderate/low-intensity recovery periods. Although this is a general description of the complex activity patterns experienced in such events, it currently provides the best means of directly assessing the physiological response to this type of exercise. During a single short (5- to 6-second) sprint, adenosine triphosphate (ATP) is resynthesised predominantly from anaerobic sources (phosphocreatine [PCr] degradation and glycolysis), with a small (<10%) contribution from aerobic metabolism. During recovery, oxygen uptake (V-dotO2) remains elevated to restore homeostasis via processes such as the replenishment of tissue oxygen stores, the resynthesis of PCr, the metabolism of lactate, and the removal of accumulated intracellular inorganic phosphate (Pi). If recovery periods are relatively short, V-dotO2 remains elevated prior to subsequent sprints and the aerobic contribution to ATP resynthesis increases. However, if the duration of the recovery periods is insufficient to restore the metabolic environment to resting conditions, performance during successive work bouts may be compromised. Although the precise mechanisms of fatigue during multiple sprint work are difficult to elucidate, evidence points to a lack of available PCr and an accumulation of intracellular Pi as the most likely causes. Moreover, the fact that both PCr resynthesis and the removal of accumulated intracellular Pi are oxygen-dependent processes has led several authors to propose a link between aerobic fitness and fatigue during multiple sprint work. However, whilst the theoretical basis for such a relationship is compelling, corroborative research is far from substantive. Despite years of investigation, limitations in analytical techniques combined with methodological differences between studies have left many issues regarding the physiological response to multiple sprint work unresolved. As such, multiple sprint work provides a rich area for future applied sports science research.

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Multiple sprint work : physiological responses, mechanisms of fatigue and the influence of aerobic fitness.

1H NMR has detected both the deoxygenated proximal histidyl NδH signals of myoglobin (deoxyMb) and deoxygenated Hb (deoxyHb) from human gastrocnemius muscle. Exercising the muscle or pressure cuffi...

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Comparative analysis of NMR and NIRS measurements of intracellular PO2 in human skeletal muscle

The present study evaluated whether intracellular partial pressure of O2 ( P O 2 ) modulates the muscle O2 uptake (V˙o 2) as exercise intensity increased. Indirect calorimetry followedV˙o 2, wherea...

https://www.physiology.org/doi/pdf/10.1152/ajpregu.1999.277.1.R173

Myoglobin desaturation with exercise intensity in human gastrocnemius muscle

1H-NMR experiments have determined intracellular O2 consumption (Vo2) with oxymyoglobin (MbO2) desaturation kinetics in human calf muscle during plantar flexion exercise at 0.75, 0.92, and 1.17 Hz...

Control of respiration and bioenergetics during muscle contraction.

The proximal histidyl NδH signal of myoglobin is detectable in 1H NMR spectra of myocardial and skeletal muscle, and its intensity reflects the intracellular oxygenation. At 1.5 Tesla (T), the typical field strength of clinical magnetic resonance imaging (MRI) magnets, the paramagnetic relaxation contribution decreases sufficiently to permit the implementation of chemical shift imaging technique to map the spatial distribution of the deoxy Mb NδH signal from human gastrocnemius muscle. One and two-dimensional chemical shift imaging experiments reveal clearly the localized deoxy Mb signal in muscle and consequently the spatial distribution of the cellular oxygenation. The results indicate the feasibility to assess the pO2 in tissue regions and to directly study the regulation of oxidative metabolism in human tissue. Copyright © 1999 John Wiley & Sons, Ltd.

Tuan Khanh Tran

Papers

Comparative analysis of NMR and NIRS measurements of intracellular PO2 in human skeletal muscle

Myoglobin desaturation with exercise intensity in human gastrocnemius muscle

Control of respiration and bioenergetics during muscle contraction.

Spatial distribution of deoxy myoglobin in human muscle: an index of local tissue oxygenation

Role of oxygen in limiting respiration in the in situ myocardium.