Sex differences in adaptation to intermittent post-exercise sauna bathing in trained middle-distance runners

Abstract

Background: The purpose of this study was to investigate the effect of sex on the efficacy of intermittent post-exercise sauna bathing to induce heat acclimation and improve markers of temperate exercise performance in trained athletes.

Methods: Twenty-six trained runners (16 female; mean ± SD, age 19 ± 1 years, V̇O_2max F: 52.6 ± 6.9 mL⋅kg^-1⋅min^-1, M: 64.6 ± 2.4 mL⋅kg^-1⋅min^-1) performed a running heat tolerance test (30 min, 9 km⋅h^-1/2% gradient, 40 °C/40%RH; HTT) and temperate (18 °C) exercise tests (maximal aerobic capacity [V̇O_2max] and lactate profile) pre and post 3 weeks of normal exercise training plus 29 ± 1 min post-exercise sauna bathing (101-108 °C) 3 ± 1 times per week.

Results: Females and males exhibited similar reductions (interactions p > 0.05) in peak rectal temperature (- 0.3 °C; p < 0.001), skin temperature (- 0.9 °C; p < 0.001) and heart rate (- 9 beats·min^-1; p = 0.001) during the HTT at post- vs pre-intervention. Only females exhibited an increase in active sweat glands on the forearm (measured via modified iodine technique; F: + 57%, p < 0.001; M: + 1%, p = 0.47). Conversely, only males increased forearm blood flow (measured via venous occlusion plethysmography; F: + 31%, p = 0.61; M: + 123%; p < 0.001). Females and males showed similar (interactions p > 0.05) improvements in V̇O_2max (+ 5%; p = 0.02) and running speed at 4 mmol·L^-1 blood lactate concentration (+ 0.4 km·h^-1; p = 0.001).

Conclusions: Three weeks of post-exercise sauna bathing effectively induces heat acclimation in females and males, though possibly amid different thermoeffector adaptations. Post-exercise sauna bathing is also an effective ergogenic aid for both sexes.

Fig. 1

Schematic of the experimental design. Females and males in the intermittent post-exercise sauna bathing intervention group (SAUNA) and control group (CON) completed temperate exercise tests (18 °C) consisting of lactate profile (LP) and maximal aerobic capacity (V̇O_2max) tests, a running heat tolerance test (HTT; 30 min, 9 km·h⁻¹/2% gradient, 40 °C/40%RH), and a plasma volume assessment at baseline (Pre) and following three weeks (Post) of sauna intervention or control. Respective tests were completed ~ 28 days apart. Black bars indicate weeks

Fig. 2

Changes (Δ) in body temperature responses during the running heat tolerance test (HTT; 40 °C, 40%RH) from baseline (Pre) to following (Post) the 3-week post-exercise sauna bathing intervention. Females are represented by circles and males by triangles. Horizontal black lines and error bars represent the group mean ± SD. *Significant difference in Pre vs Post (p < 0.05). T_rec, rectal temperature; T_sk, skin temperature; T_recRISE, rise in rectal temperature

Fig. 3

Changes (Δ) in thermoeffector responses during the running heat tolerance test (HTT; 40 °C, 40%RH) from baseline (Pre) to following (Post) the 3-week post-exercise sauna bathing intervention. Females are represented by circles and males by triangles. Horizontal black lines and error bars represent the group mean ± SD *Significant difference in Pre vs Post (p < 0.05). FBF, forearm blood flow

Fig. 4

Heart rate recovery from submaximal exercise in temperate conditions (18 °C) in females (circles) and males (triangles) at baseline (Pre; open) vs following (Post; filled) the 3-week post-exercise sauna bathing. *Significant difference at Pre vs Post (p < 0.05);