Muscle oxygenation measured by near-infrared spectroscopy during resistance training: A scoping review

Near-infrared spectroscopy (NIRS) is a noninvasive optical technique used to estimate local muscle oxygenation by measuring hemoglobin-related variables and muscle oxygen saturation. This information helps understand how skeletal muscles respond to diverse types and intensities of resistance training, giving a clearer picture of metabolic activity during exercise. This scoping review aimed to examine the role of NIRS as a monitoring tool in resistance training and to synthesize existing evidence on its potential applications. A systematic scoping review was conducted across five specific electronic databases: PubMed, Scopus, Cochrane Library, SPORTDiscus, and Medline (EBSCO). A total of 1658 records were identified, with 78 studies included. Most focused on male participants and single-joint exercises, especially knee extension. The vastus lateralis was most assessed, with isometric and isokinetic contractions predominating. Intensity was typically reported as %MVC or %1RM. About 42% used external interventions (e.g., supplementation, hypoxia, BFR). Continuous-wave NIRS systems were most common, and methodologies varied widely across studies. NIRS in resistance training is emerging; it offers a noninvasive way to monitor internal load, but current evidence does not support its ability to predict hypertrophy or strength outcomes. Its practical relevance remains unclear and needs further investigation.