Two strategies for the acute response to cold exposure but one strategy for the response to heat stress

Figures & data

Table 1. Physical characteristics of participants.

	FC	SC
Age (years)	21.2 ± 1.1	22.3 ± 1.7
Height (cm)	184.0 ± 5.1	183.3 ± 5.8
Mass (kg)	77.5 ± 5.9	79.1 ± 8.3
Body surface area (m^2)	2.02 ± 0.03	2.00 ± 0.01
Mean subcutaneous fat (mm)	10.4 ± 2.9	11.8 ± 4.1
Body mass index (kg/m^2)	22.8 ± 3.1	21.6 ± 3.9
Body fat (%)	14.6 ± 4.2	16.9 ± 5.5

FC, fast cooling group; SC, slow cooling group. Values are means ± standard deviation.

Figure 1. An example of reflexes at rest and during maximal voluntary contraction (MVC) before and after passive body heating (original data obtained from one participant).

Figure 2. Changes in V-wave response before and after passive body heating. *p < 0.05, compared with before; FC, fast cooling group; SC, slow cooling group. Values are means ± SD.

Table 2. VO₂ and metabolic rate (MR)*.

	FC		SC
	Before	After	Before	After
VO2 (mL/min/kg)	3.8 ± 0.5	6.5 ± 0.8*	3.9 ± 0.7	5.7 ± 0.5*
MR (W/m^2)	24.7 ± 6.5	61.3 ± 12.5*	26.3 ± 10.8	52.3 ± 9.4*

p < 0.05, compared with before. FC, fast cooling group; SC, slow cooling group. Values are means ± SD.

Table 3. Voluntary and electrically induced skeletal muscle properties before and after passive body heating.

	FC		SC
	Before	After	Before	After
MVC (Nm)	148.8 ± 34.2	136.5 ± 40.3	168.8 ± 43.8	164.1 ± 41.2
CAR (%)	99.4 ± 1.6	99.5 ± 2.1	99.6 ± 1.6	99.1 ± 2.1
P1 (Nm)	16.5 ± 5.8	16.4 ± 5.9	20.1 ± 5.8	18.8 ± 4.9
P20 (Nm)	86.4 ± 25.4	79.7 ± 21.9	96.1 ± 23.3	89.8 ± 21.5
P100 (Nm)	97.8 ± 27.1	106.5 ± 28.2	85.9 ± 23.6	95.9 ± 28.7
P1/P100 (%)	16.7 ± 2.4	19.1 ± 3.1	18.9 ± 4.1	20.3 ± 3.5
HRT (ms)	97.2 ± 14.4	93.8 ± 23.1	96.1 ± 18.4	92.5 ± 24.4

CAR, central activation ratio; FC, fast cooling group; HRT, half-relaxation time; MVC, maximal voluntary contraction; Nm, Newton meter; P1, P20, P100, 1 Hz, 20 Hz, 100 Hz electrical stimulus, respectively; P1/P100, 1/100 Hz ratio; SC, slow cooling group. Values are means ± SD.

Table 4. Spinal reflex excitability before and after passive body heating.

Amplitude (mV)					Latency (ms)
FC		SC			FC		SC
Before	After	Before	After		Before	After	Before	After
4.6 ± 0.2	4.5 ± 0.2	4.6 ± 0.2	4.4 ± 0.4	Mmax	13.9 ± 1.7	12.4 ± 1.8*	14.2 ± 1.8	12.5 ± 1.5*
3.3 ± 1.1	2.1 ± 1.1*	3.0 ± 1.1	1.5 ± 1.2*	Hmax	37.9 ± 2.4	35.5 ± 2.4*	37.5 ± 2.2	34.5 ± 2.3*
0.7 ± 0.3	0.5 ± 0.2*	0.7 ± 0.3	0.4 ± 0.3*	Hmax/Mmax

*p < 0.05, compared with before. FC, fast cooling group; SC, slow cooling group. Values are means ± SD.

Table 5. The changes in maximal voluntary contraction (MVC) and central activation ratio (CAR) during 1-min MVC.

	FC		SC
	Before	After	Before	After
MVC (% to control)	64.4 ± 14.1	57.8 ± 12.1	58.3 ± 11.9	53.2 ± 9.1
CAR (%)	87.9 ± 9.2	82.8 ± 12.5	77.8 ± 12.1*	74.6 ± 12.3*

*p < 0.05, compared with before. FC, fast cooling group; SC, slow cooling group. Values are means ± SD.

Table 6. Cognitive performance before and after passive body heating.

	FC		SC
	Before	After	Before	After
Unpredictable task switching (odd/even, s)	0.56 ± 0.05	0.55 ± 0.05	0.59 ± 0.08	0.59 ± 0.08
Forward digit-span task (mean digit span, no.)	6.6 ± 0.1	6.6 ± 0.8	6.4 ± 0.5	6.4 ± 0.6
Forced-choice recognition memory test (correct sample match, no.)	7.5 ± 0.9	7.7 ± 1.3	7.6 ± 1.1	7.1 ± 1.9

FC, fast cooling group; SC, slow cooling group. Values are means ± SD.

Table 7. The blood variables before and after passive body heating.

	FC		SC
	Before	After	Before	After
Neutrophils (%)	50.0 ± 9.2	55.7 ± 14.5	47.8 ± 9.3	59.9 ± 11.1
Lymphocytes (%)	35.8 ± 7.2	32.6 ± 12.1	39.7 ± 8.9	30.4 ± 10.8
Monocytes (%)	9.7 ± 3.1	9.1 ± 1.9	10.1 ± 1.8	8.8 ± 1.9
Cortisol (nmol/L)	467.9 ± 85.3	672.3 ± 100.7*	476.9 ± 82.3	679.8 ± 87.4*
Corticosterone (nmol/L)	47.9 ± 40.2	84.1 ± 50.2*	47.8 ± 21.7	69.5 ± 27.9*
IL-6 (pg/mL)	15.4 ± 23.4	17.1 ± 27.1	12.4 ± 8.6	11.7 ± 7.4
TNF-α (pg/mL)	4.6 ± 0.8	4.5 ± 0.5	5.4 ± 4.1	4.9 ± 1.4
Epinephrine (ng/mL)	2.9 ± 1.6	4.4 ± 6.1*	1.9 ± 1.3	4.7 ± 4.6*
Norepinephrine (ng/mL)	6.7 ± 3.5	17.1 ± 8.2*	5.8 ± 2.9	15.9 ± 7.7*

*p < 0.05, compared with before. FC, fast cooling group; SC, slow cooling group; IL-6, interleukin 6; TNF-α tumour necrosis factor-alfa. Values are means ± SD.