Acute and short-term effects of all-type whole-body exercise on cortical oxygenated hemoglobin concentrations in healthy adults: A systematic review and meta-analysis

INTRODUCTION: Exercise benefits cognition, particularly in older adults. During exercise, brain activity may increase blood flow and oxygen delivery. Functional near-infrared spectroscopy (fNIRS) enables the assessment of cortical activity by measuring changes in oxygenated (HbO) and deoxygenated hemoglobin (HbR). This review examined the acute and short-term effects of whole-body exercise on HbO concentration in healthy adults. METHOD: We searched PubMed, Embase and Web of Science for studies involving healthy adults performing any type of whole-body exercise, with fNIRS measurements taken during or shortly after the exercise. We performed multilevel meta-analyses using R studio package Metafor 4.8-0. RESULTS: 29 studies were included in the quantitative analyses. Exercises mainly involved walking, cycling, or coordination (5-60 min, low to vigorous intensity). Overall, HbO concentration increased during exercise versus baseline (pooled standardized mean g=0.56; 95% CI: 0.31-0.82) with no significant relationship with brain region, exercise type, exercise duration or gender (p > 0.05). Acute effects are stronger with increased exercise intensity (low, g=0.24; moderate, g=0.64; vigorous, g=0.92; p < 0.001) and for higher age (old, g=0.83; young g=0.50; p < 0.001). HbO concentration shows a trend towards an increase between pre- and postexercise (pooled standardized mean g=0.61; 95% CI: -0.03-1.2371; p = 0.058). Short-term effects were significantly related to exercise intensity (low, g=-0.04; moderate, g=1.16; vigorous, g= 1.22; p < 0.001), but not to brain area, exercise type, exercise duration or gender (p > 0.05). CONCLUSION: Exercise increases HbO concentration during exercise. Exercise intensity appeared a key factor to increase impact on the brain both during and shortly after exercise.