Background: Interest in clothing that reflects far infrared (FIR) radiation naturally emitted by the body during and after exercise has increased based on the assumption that this can increase arterial and venous blood flow. Indeed, in vitro and animal model research seems to report promising effects of FIR on the nitric oxide pathway and microcirculation. However, to date, there are no well controlled studies investigating the effect of FIR garments on resting microvascular and macrovascular function in humans. Thus, the aim of this study was to examine the acute effects of wearing FIR arm garments on vascular function.
Methods: Thirty-one male recreational sport practitioners (4.9 ± 3.3 h of sport/week; 32.1 ± 9.5 years; 178.6 ± 7.9 cm; 74.1 ± 11.2 kg; 23.2 ± 2.5 kg/m2 (mean ± SD)) completed four visits: repeatability measurements (two sessions), placebo, and FIR conditions in random order. Measurements (i.e., without arm garment) of brachial artery diameter and blood flow, carotid-radial pulse wave velocity (CR-PWV), as well as total-, oxy-, and deoxy-hemoglobin were completed after 15 min of rest and repeated after wearing FIR or placebo arm garments for 25 min, 40 min, and 50 min. Two skin sensors were positioned on the upper arm and the forearm to continuously record skin temperature and pressure under the garment.
Results: The main results were that at all time points, compared to placebo, FIR did not significantly affect brachial artery diameter and blood flow, CR-PWV, or total hemoglobin (condition × time interaction: p = 0.22, 0.54, 0.51, 0.96, respectively). Moreover, no significant condition × time × sensor position interaction effect was found in skin temperature (p = 0.99). However, pressure under garment was significantly higher under the FIR condition compared to placebo (+53%, p = 0.01, 95% confidence interval: FIR: 1.64-2.92 mmHg; placebo: 0.88-2.14 mmHg) while microvascular parameters were unchanged.
Conclusion: Contrary to our hypothesis, wearing an FIR arm garment at rest does not lead to an improvement of either macro or microvascular function. These results suggest limited benefits in the sports context, notably during recovery.

