Near-Infrared Spectroscopy in the Pathophysiology, Diagnosis, and Exercise-Based Management of Muscle Oxygenation...

Muscle oxygen nation impairment, defined as a mismatch between oxygen delivery, distribution, and oxidative utilization in active skeletal muscle, contributes to exercise intolerance and functional decline. Near-infrared spectroscopy (NIRS) has emerged as the leading non-invasive tool for monitoring local muscle oxygenation, but its clinical translation and optimal exercise-based management remain incompletely defined. This scoping review aimed to (1) synthesize the pathophysiology of muscle oxygenation impairment across the oxygen transport cascade, (2) evaluate NIRS-based diagnostic protocols, and (3) review exercise-based interventions targeting muscle oxygenation. The review followed PRISMA-ScR guidelines and was prospectively registered in OSF (DOI: 10.17605/OSF.IO/QW8R3) and PROSPERO (CRD420261365040). PubMed, Web of Science, Scopus, Cochrane CENTRAL, EMBASE, PEDro, and ClinicalTrials.gov were searched through to April 2026. Methodological quality was appraised using the PEDro scale, the Downs and Black checklist, and the Newcastle-Ottawa Scale. A total of 61 studies (2003-2025) were included, with fair-to-good methodological quality (PEDro 3-8, mean 5.3; Downs and Black 15-24, mean 18.6; Newcastle-Ottawa 5-8, mean 6.5). Regarding pathophysiology, muscle oxygenation impairment is a cascade-level phenomenon with four mechanistically distinct phenotypes corresponding to the dominant site of impairment, each with characteristic NIRS signatures. Regarding diagnostic assessment, NIRS has shown value in selected contexts including a validated threshold for peripheral artery disease, but most studies report group-level correlations without deriving receiver operating characteristic curves at validated thresholds, which together with device and calibration heterogeneity limits clinical translation. Regarding exercise-based interventions, adaptations align with the underlying cascade lesion, sprint and high-intensity interval training enhance oxidative capacity, while walking-based and vascular-targeted programs preferentially improve microvascular function. These findings support a unifying framework in which the site of cascade impairment guides diagnostic protocol selection and exercise prescription. The proposed cascade lesion phenotyping schema is hypothesis-generating and requires prospective validation.