Table 2.

Result of review of the included studies.

Authors	Design	Experimental Group					Comparative Group	Outcome Variables	Conclusion and Implementation of Evidence	Effect of Water
		Intervention	Time (T) for Measurement	Participants	Time Per Session	Total Session and Period
Brunt et al. [18]	One group pre- and post-test	• Hot warm water immersion of the shoulder (40.5 °C) for 25–30 min • Sitting up in waist-level water in a tub for 60 min	• Pre-treatment (T1) • Post-treatment (T2) • Post-I/R (T3)	• Young, healthy men (n = 5) and women (n = 5) • Aged 23 ± 6 years (mean) • Sample size was calculated using SigmaPlot 11.0	60 min	Single	-	• Brachial artery flow-mediated dilation as endothelial function • Rectal temperature • Heart rate	• There was a significant interaction effect of intervention × time point on FMD% • Rectal temperature increased to a peak of 38.9 ± 0.2 °C • Heart rate increased from 81 ± 18 beats/min at T1 to 127 ± 18 beats/min during hot warm immersion • Hot water immersion results in potential protective effects against I/R-induced vascular dysfunction	Thermal effect
Shimodozono et al. [19]	One group pre- and post-test	• Warm immersion to subclavicular level (41 °C) • Subjects were reclined on a stretcher at an angle of 36° in a bathtub	• Pre-treatment (T1) • Immediately post-treatment (T2) • 30 min after treatment (T3)	• Healthy men (n = 7) • Aged 39.7 ± 6 years (mean) • No mention of calculation of sample size	10 min	Single	-	• Adiponectin and leptin, as adipocyte-derived hormones • Glucose • Insulin • Lipids (T-chol, LDL-C, HDL-C, TG, and FFA) • CBC (RBC, Hb, Ht, WBC, and Plt)	• Leptin levels significantly increased at T2 and T3 after warm immersion • Some parameters (insulin, T-Chol, RBC, Hb, Ht, and WBC) significantly increased immediately (T2) after warm immersion • A single warm immersion for 10 min may modulate leptin and adiponectin profiles in healthy men	Thermal effect
Bailey et al. [20]	Randomized controlled trial	• Warm water immersion (42 °C) • Subjects were seated in a tank with water up to top-sternal level	• Pre-treatment (T1) • Post-treatment (T2)	• Healthy women (n = 9) • Aged 25 ± 5 years (mean) • No mention of calculation of sample size	30 min	24 times for 8 weeks	• Control (n = 9): cycling (70% HRmax)	• Brachial artery flow-mediated dilation • Cardiorespiratory fitness	• Two outcome variables improved after both warm water intervention and cycling • Passive heat training through warm water intervention can be a useful alternative to exercise training.	Thermal effect
Costello et al. [21]	Randomized crossover trial	• Cold water immersion (14 ± 1 °C) • Subjects were seated in tank with water up to umbilicus level		• Healthy men (n = 8) and women (n = 6) • Aged 21.9–25.1 years (mean) • No mention of calculation of sample size	30 min	Single	• Self-control (crossover) (n = 14): tepid water immersion (28 ± 1 °C)	• Knee joint position sense	• No significant difference between pre- and post-test for both cold and tepid water • Cold water immersion cannot reduce knee joint position sense	Thermal effect
Herrera et al. [22]	Quasi-experimental	• Cold water immersion (10 °C) • Subjects were seated in an acrylic container with water below the level of the head of the fibula	• Pre-treatment (T1) • Post-treatment (T2)	• Healthy men (n = 18) and women (n = 18) • Aged 20.5 ± 1.9 years (mean) • Sample size was calculated using Stata	15 min	Single	• Comparative 1 (n = 12): ice massage • Comparative 2 (n = 12): ice pack	• Skin temperature • Nerve conduction parameters	• Cold water immersion is the most effective modality for changing the nerve conduction parameter	Thermal effect
Hu et al. [23]	Randomized crossover trial	• Warm water immersion (41–43 °C) • Subjects were seated with legs and feet in a plastic bucket with the water level below the knees	• Pre-treatment (T1) • Post-treatment (T2)	• Healthy young (n = 16) and older women (n = 16) • Young women aged 25.4 ± 0.4 years (mean) and older women aged 59.8 ± 1.7 years (mean) • No mention of calculation of sample size	30 min	Single	• Self-control (crossover): sedentary seating in chairs	• Cardio-ankle vascular index indicated arterial stiffness • Tympanic temperature	• Main time effect (+) in both women • HR (↑), diastolic BP (↓) in young women • Tympanic temperature (↑) in both groups of women • Warm water immersion results in transient improvement of systemic arterial stiffness, mediated by elevation of core temperature • Repeated thermal therapy can promote cardiovascular health	Thermal effect
Wakabayashi et al. [24]	One group pre- and post-test	• Repeated mild cold water immersion (26 °C) • Subjects were seated in tank with water up to xiphoid level	• Pre-treatment (T1) • Post-treatment (T2)	• Healthy men (n = 7) • Aged 21.3 ± 0.8 years (mean) • No mention of calculation of sample size	60 min	12 times over 4 weeks	-	• Body temperature (11 regional skin temperatures) • Skin blood flow on the forearm • Metabolic heat production • Cold-induced vasodilation	• Main effect of pre- and post-test acclimation is observed in mean skin temperature • Skin blood flow was significantly lower post-test than pre-test • Index of cold-induced vasodilation was significantly lower in post-test acclimation than in pre-test acclimation • The repeated cold immersion in 26 °C water was sufficient to induce the insulative-type of cold adaptation.	Thermal effect
Brunt et al. [25]	Non-randomized trials	• Warm immersion up to the shoulder (40.5 °C) for 25–30 min and up to the waist for 60 min • Subjects stayed in hot tub until the rectal temperature reached 38.5 °C	• Pre-treatment (T1) • 1 week after treatment (T2) • 2 weeks after treatment (T3) • 4 weeks after treatment (T4) • 6 weeks after treatment (T5) • 8 weeks after treatment (T6)	• Healthy sedentary males (n = 4) and females (n = 6) • Aged 22.0 ± 1.0 years (mean) • No mention of calculation of sample size	90 min	36 times over 8 weeks	• Control (n = 10): thermo-neutral water immersion (36 °C)	• Carotid artery wall thickness and stiffness • Pulse wave velocity • Flow-mediated dilatation and post-occlusive reactive hyperemia • Endothelium-dependent dilatation	• Flow-mediated dilatation with passive heat therapy (warm immersion) was significantly elevated at 2, 6, and 8 weeks • Passive heat therapy significantly increased post-occlusive reactive hyperemia by 6 weeks • Passive heat therapy significantly reduced carotid artery wall thickness by 8 weeks • There was a significant main effect of time on the systolic blood pressure • Passive heat therapy using warm immersion results in increased endothelium-dependent dilatation and reduced arterial stiffness, wall thickness, and blood pressure.	Thermal effect
Streff et al. [26]	Randomized crossover trial	• Hot water immersion (47–48 °C) • Subjects were immersed in water up to the wrist in a 12-L tank	• Pre-treatment (T1) • Post-treatment with hot or cold water (T2) • Post-alternating treatment with hot and cold water (T3)	• Healthy men (n = 17) and women (n = 18) • Aged 24 years (median) • Sample size was calculated using G*power	75 min	Single	• Self-control (crossover): cold water immersion (3–4 °C)	• Subjective pain intensity, pain threshold, pain intolerance level using the VAS • Unpleasantness and affectivity • Physiological parameters (BP, HR, RR)	• Both pain thresholds and pain tolerance levels were significantly higher for cold water immersion than for hot water immersion • Hot water immersion produced a slightly higher subjective pain experience and was tolerated for a shorter period of time • BP was significantly higher in the cold water immersion trial • In cold water immersion, the HR parameters varied as the sympathetic activity was higher than that in hot water immersion	Thermal effect
Wijayanto et al. [27]	One group pre- and post-test	• Hot water immersion (38 °C, 40 °C, and 42 °C) • Subjects were immersed in water up to the knee level in a chamber	• Pre-treatment (T1) • 15 min after treatment (T2) • 30 min after treatment (T3) • 45 min after treatment (T4)	• Healthy men (n = 11) • Aged 22.1 ± 1.1 years (mean) • No mention of calculation of sample size	45 min	Single	-	• Short-term memory span • Rectal temperature • BP • Subjective thermal comfort and thermal sensation • Tissue oxygenation index in the pre-frontal cortex • Change in oxy-Hb level • Change in deoxy-Hb level	• Significant main effect of water temperature on change in the rectal temperature and HR after 45 min • Change in oxy-Hb increased in all three different conditions of water temperature (time effect): significantly higher in the 42 °C condition than in the 38 °C condition • Change in deoxy-Hb did not differ among the three conditions • Different temperature conditions induced little effect on cognitive functioning	Thermal effect
Kojima et al. [28]	Randomized crossover trial	• Hot water immersion (42 °C) • Subjects sat in a tank with water up to the neck	• Pre-treatment (T1) • Immediately after treatment (T2) • 15 min after treatment (T3) • 30 min after treatment (T4)	• Healthy men (n = 8) • Aged 25.4 ± 3.3 years (mean) • No mention of calculation of sample size	20 min	-	• Self-control (crossover): thermo-neutral water immersion (35 °C)	• Core temperature • Mean arterial pressure • Heart rate • Serum BDNF level • Serum S100β level • Plasma cortisol level • Plt count • Monocyte count	• Core temperature was significantly higher at T2 and T3 • BDNF level was higher at T2 and T3, and returned to the baseline at T4. • Cortisol level was lower at T2 and returned to pre-test level during the recovery period	Thermal effect
Valizadeh et al. [29]	Controlled single-blinded parallel trial	• Hot water immersion (41–42°C) • To place foot in plastic container at a height of 10 cm	• Pre-treat (T1) • Post-treat (T2)	• Healthy elderly subjects (n = 23) • Aged 67.69 ± 4.28 years (mean) • Sample size was calculated	20 min	42 times over 6 weeks	• Comparative 1 (n = 23): massage with olive oil • Control (n = 23): no treatment	• Quality of sleep and sleep patterns using PSQI instrument	• Foot bath was effective in all components except sleep efficiency and use of sleep medication • Foot bath caused 22% reduction in the prevalence of sleep disorders compared to 18% reduction with the comparative intervention	Thermal effect
Kim et al. [30]	Quasi-experimental	• Hot water immersion (40 °C) • Subjects placed their foot in a footbath machine to a height of 20 cm above the ankle	• Pre-treatment (T1) • 1 week after treatment (T2) • 2 weeks after treatment (T3) • 3 weeks after treatment (T4) • 4 week after treatment (T5)	• Healthy elderly subjects (n = 10) • Aged 81.6 ± 4.5 years (mean) • Sample size was calculated using G power • All groups (experimental, comparative, and control) were divided into the subgroups good-sleep and poor-sleep	30 min	28 times over 4 weeks	• Comparative 1 (n = 10): water immersion (36.5 °C) • Control (n = 10): no treatment	• Sleep patterns assessed using ATG machine (Mini-Mitter Co., Inc., Bend, OR, USA) • Sleep-disturbed behaviors were assessed using SDI instrument	• There were no significant differences in total sleep between groups and between measurement times • In the sleep effectiveness of the experimental group, there was a significant interaction between group and time	Thermal effect

HR: Heart Rate, BP: Blood Pressure, FFA: Free Fatty Acid, RBC: Red Blood Cell Count, WBC: white blood cell count, I/R: Ischemia-reperfusion (inflation and reperfusion using inflatable occlusion cuff), SDI: Sleep Disorders Inventory, FMD: Flow-mediated dilation, T-chol: total cholesterol, LDL-C: low-density lipoprotein, HDL-C: high-density lipoprotein, TG: triglyceride, CBC: complete blood count, Hb: hemoglobin, Ht: hematocrit, Plt: platelets, HRmax: maximum heart rate, RR: Respiratory Rate, VAS: Visual Analog Scale, PSQI: Pittsburgh Sleep Quality Index, BDNF: brain-derived neurotrophic factor.