Table 4.

Repeated sauna and athletes.

Study characteristics			Study sample		Intervention		Comparators		Health effects	Adverse side effects
Author & year	Level of evidence	Design	Pop/country	N	Sauna type	Duration	Comparator/ controls	Outcome measures	Positive/negative/negligible	None/mild/ moderate/ severe
2015 Stanley et al. [61]	III	Single-group, interrupted time series study	Elite Athletes– Males/ Australia	7	Finnish	10 days	No control group	Plasma volume changes (calculated from Hb readings); hydration status (using urine SG by digital refractometer); ergometer exercise performance measures; HRV	Positive, postexercise sauna bathing increased plasma volume after 4 days of intervention (p < 0.01)	Mild – comments of “hot and very uncomfortable, but tolerable” per thermal comfort survey conducted every 5 min during sauna sessions
2012 Zinchuk and Zhadzko [62]	III	Single-group interventional study	Male Elite Athletes/ Belarus	16	Finnish	5 months	No control group	Axillary temp; venous blood gas analysis; lipid peroxidation and free radical processes by UV and fluorescence analysis of plasma and RBCs; antioxidant estimation by α-tocopherol fluorescence analysis of plasma and RBC catalase activity; nitric oxide metabolism by spectrophotometric methods, plasma nitrate and nitrite levels	Positive, increased axillary body temp 2.6°C (p < 0.001) after first sauna and 1.9°C (p < 0.002) after course of sauna; increased pH by 0.8% (p < 0.001), decreased base excess by 20.3% (p < 0.001), increased venous O2 by 53.3% (p < 0.001), increased Hb concentration in blood by 5.2% (p < 0.001), right shift of oxy-Hb dissociation curve (decreased affinity – favours release of O2 to tissues) after 1st sauna; similar changes after final sauna (p < 0.043–p < 0.005)	None

RH = relative humidity; Hb = haemoglobin; SG = specific gravity; HRV = heart rate variability; temp = temperature; O₂ = oxygen; ROS = reactive oxygenated species; RBCs = red blood cells or erythrocytes.