Head-out immersion in hot water increases serum BDNF in healthy males

Figures & data

Figure 1. Changes in core body temperature in head-out water immersion. Data are mean ± SD. *p < 0.05, compared with before immersion. #p < 0.05, hot-HOI vs. neutral-HOI. pre: before head-out water immersion, post: at the end of head-out water immersion, post15: at 15 min after the end of head-out water immersion, post30: at 30 min after the end of head-out water immersion. Core body temperature (T_cb) at hot-HOI was significantly higher (p < 0.05) at post and was still elevated at post15, but recovered to pre level at post30. T_cb did not change during the entire neutral-HOI arm of the study. T_cb at hot-HOI at post and post15 were significantly (p < 0.05) higher than those at neutral-HOI.

Table 1. Change in heart rate (HR) and mean arterial pressure (MAP) in head-out water immersion.

	Hot-HOI					Neutral-HOI
	Pre	During	Post	Post15	Post30	Pre	During	Post	Post15	Post30
HR	64.9 ± 8.2	91 ± 15.8*	100.5 ± 11.7*	83.1 ± 12.4	78.8 ± 13	67 ± 6.5	68 ± 8.9	68.3 ± 7.4	68 ± 7.4	67 ± 8
MAP	90.6 ± 8.9	90.4 ± 7.4	88.4 ± 8.7	79.8 ± 9.2	83.3 ± 10.3	89.1 ± 7.3	90.7 ± 6.1	89.4 ± 5.9	88.6 ± 5.5	90.0 ± 5.5

Data are mean ± SD.

* p < 0.05, compared with before immersion (pre).

Hot-HOT: head-out water immersion at 42 °C, neutral-HOI: head-out water immersion at 35 °C, Pre: before head-out water immersion, during: at 5 min the start of head-out water immersion, post: at the end of head-out water immersion, post15: at 15 min after the end of head-out water immersion, post30: at 30 min after the end of head-out water immersion.

Figure 2. Changes in serum BDNF in head-out water immersion. The centre of each bar represents the mean value for each time period and the length of the bar represents the SD value. *p < 0.05, compared with before immersion. #p < 0.05, hot-HOI vs. neutral-HOI. Each figure should show one open symbol (neutral HOI) and one solid symbol (hot-HOI). See Figure 1 for definitions. Serum BDNF concentration was significantly higher (p < 0.05) at post and was still high at post15, but returned to pre level at post30. No change was observed in serum BDNF concentration throughout the study in the neutral-HOI. Serum BDNF levels of hot-HOI at post, post15 and post30 were significantly (p < 0.05) higher than those of neutral-HOI.

Figure 3. Changes in serum S100β in head-out water immersion. See Figures 1 and 2 for definitions. Serum S100β did not change throughout the hot-HOI and neutral-HOI tests, and was not significantly different between hot-HOI and neutral-HOI at the four different time points.

Figure 4. Changes in plasma cortisol in head-out water immersion. *p < 0.05, compared with before immersion. See Figures 1 and 2 for definitions. In the hot-HOI experiment, plasma cortisol level decreased (p < 0.05) at post but returned to pre level at the two recovery time points, while it did not change throughout the neutral-HOI study. Plasma cortisol was not significantly different between hot-HOI and neutral-HOI at the four different time points.

Table 2. Blood cell counts, platelet and monocytes during head-out water immersion.

	Hot-HOI				Neutral-HOI
	Pre	Post	Post15	Post30	Pre	Post	Post15	Post30
Platelet (10^4/μl)	22.1 ± 3.2	23.6 ± 3.0	23.1 ± 3.6	23.1 ± 4.4	22.1 ± 3.4	23.1 ± 3.0	23.1 ± 3.6	23.1 ± 4.4
Monocytes (10^2/μl)	2.4 ± 0.9	2.1 ± 0.8	2.2 ± 0.7	2.6 ± 0.5	3.4 ± 1.1	2.9 ± 1.1	3.2 ± 0.8	3.2 ± 0.9

Data are mean ± SD.

All data of post, post15 and post30 were not significantly different from those of the respective pre values (p > 0.05).

Hot-HOT: head-out water immersion at 42 °C, neutral-HOI: head-out water immersion at 35 °C, Pre: before head-out water immersion, post: at the end of head-out water immersion, post15: at 15 min after the end of head-out water immersion, post30: at 30 min after the end of head-out water immersion.