The Effect of Medium-Term Sauna-Based Heat Acclimation (MPHA) on Thermophysiological and Plasma Volume Responses to Exercise Performed under Temperate Conditions in Elite Cross-Country Skiers

Abstract

The influence of a series of ten sauna baths (MPHA) on thermophysiological and selected hematological responses in 14 elite cross-country skiers to a submaximal endurance exercise test performed under thermoneutral environmental conditions was studied. Thermal and physiological variables were measured before and after the exercise test, whereas selected hematological indices were studied before, immediately after, and during recovery after a run, before (T1) and after sauna baths (T2). MPHA did not influence the baseline internal, body, and skin temperatures. There was a decrease in the resting heart rate (HR: p = 0.001) and physiological strain (PSI: p = 0.052) after MPHA and a significant effect of MPHA on systolic blood pressure (p = 0.03), hematological indices, and an exercise effect but no combined effect of treatments and exercise on the tested variables. A positive correlation was reported between PSI and total protein (%ΔTP) in T2 and a negative between plasma volume (%ΔPV) and mean red cellular volume (%ΔMCV) in T1 and T2 in response to exercise and a positive one during recovery. This may suggest that MPHA has a weak influence on body temperatures but causes a moderate decrease in PSI and modifications of plasma volume restoration in response to exercise under temperate conditions in elite athletes.

Keywords: athletes; body temperature; exercise; physiological strain; plasma volume; sauna baths.

Figure 1

Experimental design. Tx—a preliminary study; T1—experimental exercise test performed before sauna bathing; T2—experimental exercise test performed after a series of ten sauna baths; ↑∕↑—a graded exercise test; ↑≈↑—a submaximal, endurance exercise test; 1—physiological measures and blood collection at rest; 2—physiological measures and blood collection immediately after the exercise test; 3—blood collection at 60 min of recovery; 4—blood collection 24 h after the exercise test.

Figure 2

Plasma protein (TP), hematocrit (HCT), and hemoglobin (Hb) concentration and plasma osmolality, mean red cellular volume (MCV); at rest (baseline), in response to exercise (Ex) (60-min exercise at constant work rate (60% power max) and during recovery (1 h R; 24 h R), before (T1) and after MPHA (T2). Data are presented as mean ± SD, n = 10 for all data; * significance of differences between control (T1) and heat acclimated person (T2) in the same time of testing.

Figure 3

Differences (% Δ) related to baseline (t0) of plasma volume (% ΔPV), total proteins (%Δ TP), hematocrit (%Δ HCT), mean red cell volume (% Δ MCV), immediately after exercise test Ex (t1−t0), as well as 60 min 1 h R (t2−t0)) and 24 h after the exercise 24 h R (t3−t0)) in the control (T1) and heat acclimated (T2) cross-country skiers. Results are presented as median and IQR; 25%–75%, n = 14 for all data. * Significance of differences between control (T1) and heat-acclimated subjects (T2) in the same time of testing, p < 0.05. (by the Wilcoxon test). Note: Friedman’s ANOVA results: (% ΔPV): T1 group: χ² df = 2, n = 14 = 9,78, p = 0.007; T2 group: χ² df = 2, n = 14 = 14.0, p = 0.000; Friedman’s ANOVA results (%Δ TP): T1 group: χ² df = 2, n = 14 = 32.7, p = 0.000; T2 group: χ² df = 2, n = 14 = 25.0, p = 0.000; Friedman’s ANOVA results: (% ΔHCT): T1 group: χ² df = 2, n = 14 = 20.03, p = 0.000; T2 group: χ² df = 2, n = 14 = 13.6, P = 0.001; Friedman’s ANOVA results: (% ΔMCV): T1 group: χ² df = 2, n = 14 = 10.3, p = 0.001; T2 group: χ² df = 2, n = 14 = 8.19, P = 0.016, # p < 0.05 vs. the respective exercise value, by the Wilcoxon test in T1, and p < 0.05 vs. the respective exercise value, by the Wilcoxon test in T2.