Thermal and cardiovascular heat adaptations in active adolescents following summer

Figures & data

Table 1. Participant characteristics pre- and post-summer, including $\dot{\mathrm{V}}$O_2peak and reported Tanner stage.

Characteristic	Pre-summer	Post-summer
Age (y)	14.6 ± 1.0	14.9 ± 1.0
Height (m)	1.70 ± 0.08	1.71 ± 0.08
Body mass (kg)	56.84 ± 9.05	58.22 ± 9.25
Body fat (%)	18.4 ± 4.9	18.2 ± 4.8
$\dot{V}$O2peak (mL·kg^−1·min^−1)	60.4 [56.2, 64.6]	61.6 [57.4, 65.8]
Tanner stage (n = 15)
Pre-pubertal (Stage 1)	0	0
Mid-pubertal (Stage 2–4)	12	11
Late-pubertal (Stage 5)	3	4

Data presented as mean ± standard deviation, except for $\dot{\mathrm{V}}$O_2peak presented as posterior mean and 90% credible interval, and Tanner stage presented as counts. $\dot{\mathrm{V}}$O_2peak; peak oxygen consumption.

Table 2. Gastro-intestinal and skin temperature, heart rate, hemoglobin mass, and plasma and blood volume at rest pre- and post-summer.

Outcome variable	Pre-summer	Post-summer	Mean difference [90% CrI; Pd]
Gastro-intestinal temperature (°C)	37.28 [37.17, 37.39]	37.09 [36.98, 37.19]	−0.19 [−0.31, −0.07; 99%]
Heart rate (beats·min^−1)	80 [75, 85]	73 [68, 78]	−7 [−10, −3; 100%]
Skin temperature (°C)	32.15 [31.78, 32.52]	32.14 [31.77, 32.50]	−0.02 [−0.45, 0.42; 52%]
Hemoglobin mass (g·kg^−1)	11.6 [10.9, 12.3]	11.9 [11.2, 12.6]	0.3 [−0.6, 1.2; 73%]
Plasma volume (mL·kg^−1)	47.5 [45.1, 49.9]	46.9 [44.5, 49.4]	−0.5 [−3.6, 2.5; 61%]
Blood volume (mL·kg^−1)	78.8 [74.9, 82.7]	77.6 [73.7, 81.7]	−1.1 [−6.0, 3.9; 63%]

Data presented as posterior means and 90% credible intervals [CrI]. Model estimates were based on the arithmetic mean of $\dot{V}$O2peak. Pd; probability of direction.

Figure 1. Gastro-intestinal temperature during 45 min of walking at 60% $\dot{\mathrm{V}}$O_2peak in 40°C and 30% relative humidity pre- and post-summer. The thick lines represent the population predicted means surrounded by 90% credible intervals. Model estimates are based on the arithmetic mean of $\dot{\mathrm{V}}$O_2peak. The model was implemented using data from 5-min intervals. Observed data are visualized at 15-min intervals.

Figure 2. Heart rate during 45 min of walking at 60% $\dot{\mathrm{V}}$O_2peak in 40°C and 30% relative humidity pre- and post-summer. The thick lines represent the population predicted means surrounded by 90% credible intervals. Model estimates are based on the arithmetic mean of $\dot{\mathrm{V}}$O_2peak. The model was implemented using data from 5-min intervals. Observed data are visualized at 15-min intervals.

Table 3. Gastro-intestinal temperature, heart rate, whole-body sweat loss, and sweat sodium concentration during the heat response test pre- and post-summer.

Outcome variable	Pre-summer	Post-summer	Mean difference [90% CrI; Pd]
Rise in Tgi (°C)	1.78 [1.57, 1.99]	1.56 [1.36, 1.76]	−0.22 [−0.48, 0.04; 92%]
End-exercise Tgi (°C)	38.95 [38.72, 39.18]	38.60 [38.37, 38.82]	−0.35 [−0.63, −0.07; 98%]
Rise in heart rate (beats·min^−1)	97 [87, 106]	92 [83, 101]	−5 [−14, 4; 81%]
Heart rate (beats·min^−1)	187 [178, 196]	180 [172, 189]	−7 [−16, 2; 89%]
WBSL (L)	0.78 [0.67, 0.90]	0.82 [0.70, 0.93]	0.03 [−0.06, 0.12; 73%]
Sweat [Na^+] (mmol·L^−1)
Back	69	66	−3
	[60, 78]	[50] 75]	[−13, 6; 73%]
Forearm	65	57	−8
	[50] 72]	[51] 65]	[−14, −1; 97%]

Data presented as posterior means and 90% credible intervals [CrI]. Model estimates were based on the arithmetic mean of $\dot{V}$O_2peak. T_gi; Gastro-intestinal temperature, LSR; local sweat rate, Pd; probability of direction, Sweat [Na+]; sweat sodium concentration, WBSL; whole-body sweat loss.

Figure 3. Mean maximum dry-bulb and wet-bulb globe temperature from October 1^st 2022 to March 31^st 2023. The individual data points represent weekly averages. The vertical dashed black lines represent the start and end of summer, respectively.

Data availability statement

The data and associated code used for analyses are available from the corresponding author upon reasonable request.