Table 2.

Longitudinal natural cold air exposure.

Reference	Study Sample	Habituation Length	Habituation Temperature	Cold Testing Procedure	Results/Findings
Carlson [139]	7 M	16–18 hr daily exposure for 14 days	Outside air temperature varied from −5 to −17°C; wore adequate clothing to prevent discomfort	Passive observation to natural exposure	Slower initial rate of hand Tsk ↓ with hand Tsk maintained at a greater temperature after 14 days of exposure; CIVD amplitude ↓ over the 14 days
Bruck [66]	9 M (Study B)	10 day, 24 hr exposure	−2 to 14°C	Pre and Post cold test: 30 min at 28°C, linear decrease of 0.5°C per minute to 5 to −5°C for 1 hr or until shivering	Habituation temperature deemed a ‘mild’ cold stress; only 4/9 subjects saw cold habituation: shivering threshold occurred at ↓Tb, ↑ resting metabolic rate, cold sensations occurred at ↓ Tb, and Tes ↓ following the 10 day exercise
Bodey [140]	7 M Caucasians	1 continuous year in Antarctica	Outdoors: ~0 to −20°C with mean wind speed as high as 10 m/s for 2–3 hrs per day; Indoors: 21–23°C with brief but frequent lightly clad pulses of ambient cold	Standard cold stress test of 10°C for 2 hrs + rewarming completed before (in Melbourne) and 4 times during the year in Antarctica	Within a month of arriving in Antarctica, ↓ peripheral temperatures and ↓ Tre cooling rate in the second hour of cold stress; After 9 months, ↑ Tsk and ↓ Tre in the second hour of cold stress along with an ↑ in peripheral rewarming rate; ↓ in plasma cortisol, ↑adrenaline excretion established in late standard cold stresses; ↑ delay in the onset of shivering, ↓ Tsk at shivering onset, and ↓ NE observed in late standard cold stress
Bittel [141]	1 M French doctor	63 day journey from arctic Canada to the North Pole (1100 total km)	Ambient temperatures varied between −52 and −12°C; wore light-weight insulated clothing, skied pulling a 50 kg sled daily	Pre and post cold test: 2 hr exposure to 1°C (wind speed 0.8 m/s, RH 40%) laying on a wire mesh bed wearing only swimming trunks	After his journey, a general hypothermic-hypometabolic adaptation characterized by a ↓ Trec and metabolic heat production and an ↑ skin temperature of the extremities; authors state that tympanic temperature, as representative of the CNS temperature, ↑ despite Trec ↓ suggests a redistribution of blood volume to the CNS
Livingstone [117]	4 M Canadians	91 day North Pole ski expedition	Unknown	Passive 10°C air exposure for 90 min + Finger 0°C 30 min ice water bath immersion	10°C air: After 91 days of exposure, ↑ time to onset of shivering, smaller ↑ in metabolism in response to cold; 0°C water bath: ↑ CIVD response
Muller [67]	14 M; 6 cold-acclimated American football players	2 years	2 hrs/day at 0°C (range −8 to 7°C) from January-March	90 min resting at 5°C, 30 min exercising at 50% VO2peak at 5°C, 60 min post-exercise recovery in 5°C	At 5°C rest, cold-acclimated football players had ↑ finger temperatures, ↓ metabolic rate, ↓ hand pain, ↓ negative mood, ↔ dexterity; With continuous exercise in 5°C, cold-acclimated football players had ↑ finger rewarming after 20 min that occurred at ↓ Tc