The effectiveness of far-infrared irradiation on foot skin surface temperature and heart rate variability in healthy adults over 50 years of age

Abstract

Background: Far-infrared irradiation (FIR) is used in the medical field to improve wound healing, hemodialysis with peripheral artery occlusive disease, and osteoarthritis but seldom used in ameliorating poor lower extremity circulation. The purpose of this study was to evaluate the effect of FIR on changes in foot skin surface temperature (FSST) and autonomic nerve system (ANS) activity to evaluate its effectiveness in improving lower limb circulation. Methods: A randomized controlled study was conducted. Subjects (n = 44), all over the age of 50 years and satisfying the inclusion criteria, were randomly allocated into 2 groups. The intervention group received FIR on a lower limb for 40 minutes and the control group received no intervention. Left big toe (LBT), right big toe (RBT), left foot dorsal (LFD), right foot dorsal (RFD) surface skin temperature, autonomic nervous activity, and blood pressure were assessed. Results: The main results were skin surface temperature at the LBT increased from 30.8 ± 0.4°C to 34.8 ± 0.4°C, at RBT increased from 29.6 ± 0.4°C to 35.3 ± 0.4°C and LFD increased from 31.9 ± 0.3°C to 36.4 ± 0.4°C, RFD increased from 30.7 ± 0.3°C to 37.7 ± 0.2°C. FIR caused a significant increase of the FSST ranging in a 4°C to 7°C increase after 40 minutes irradiation ( P < .001). The ANS low-frequency (LF) and high-frequency (HF) activity showed a statistically significant increase in the FIR group ( P < .05) but not the LF/HF ratio. Conclusion: FIR significantly increased the FSST from between 4°C and 7°C after 40 minutes irradiation, which might improve lower extremity circulation and regulation of ANS activity.

Crossover trial of the effects of a far-infrared heater that heats the feet with ceramic balls on autonomic nervous activity and mood states

“… 7 Other studies of the local effects of exposing the lower extremities to FIR noted improved sleep 9 and parasympathetic nervous system activation. 1 Those studies similarly show that exposure of the lower extremities to FIR provided systemic rather than just local relaxation. Heating the lower extremities with FIR emitted from the ceramic balls of the Omotenashi Ashiyu device used in this study presumably affected autonomic nervous system activity via afferent vagal fibers.…”

“…In other studies of FIR exposure from distances of 20–30 cm, autonomic nervous system changes appeared from 15 min to 40-minute heating sessions. 1 , 2 In a study that used a warm-water footbath, brain wave changes occurred after 5 min of use, and HF changed after less than 10 min of use. 26 Footbath use quickly provided relaxation as in our study.…”

“…Effects included activation of the sympathetic nervous system with 40 min of exposing the upper arms to a heater located 30 cm from the skin 2 and improved parasympathetic nervous system activity from 25 min during 40 min of exposing the legs to FIR from a distance of 20 cm from the skin. 1 Other studies that used mood state scales for subjective evaluation found that 15 min in an FIR dry sauna reduced anxiety, depression, and fatigue, 3 increased parasympathetic nervous system activity, and decreased sympathetic nervous system activity in patients with chronic heart failure. 11 As these findings show, various relaxing effects of convection currents in dry saunas and FIR exposure directed from a source a certain distance from the body have been demonstrated.…”

“…Different FIR heaters employ a variety of heating systems. Classified according to the location of the heater relative to the body, these include heaters that direct FIR rays toward the skin surface from a certain distance, 1 , 2 dry saunas and other heaters that use convection currents, 3 , 4 and heaters that surround the surface of the skin with heated ceramic balls or other materials. 5 , 6 Classified according to the range of heating, heaters can heat the entire body or only parts of the body, such as the back or lower extremities.…”

“…Effects included activation of the sympathetic nervous system with 40 min of exposing the upper arms to a heater located 30 cm from the skin 2 and improved parasympathetic nervous system activity from 25 min during 40 min of exposing the legs to FIR from a distance of 20 cm from the skin. 1 …”