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Reduced dexterity is a major problem in cold weather, with a need for a countermeasure that increases hand (Thand) and finger (Tfing) temperatures and improves dexterity. The purpose of this study was to determine whether electric heat (set point, 42°C) applied to the forearm (ARM, 82 W), face (FACE, 9.2 W), or combination of both (COMB, 91.2 W), either at the beginning of cold exposure (COLD; 0.5°C, 120 min; 2 clo insulation, seated, bare-handed) or after Tfing fell to 10.5°C [delayed trials (D)], improves Thand, Tfing, dexterity, and finger key pinch strength (Sfing). Volunteers ( n = 8; 26 ± 9 yr) completed 7 experimental trials in COLD: ARM, ARM-D, FACE, FACE-D, COMB, COMB-D, and no heating (CON). Temperatures were measured before (BASE) and throughout COLD. Tests of dexterity [Purdue Pegboard assembly (PP) and magazine loading (MAGLOAD)] and Sfing were measured at BASE and after 45 and 90 min of COLD. Data presented are at minute 90. Thand was warmer ( P < 0.001) during ARM (18.0 ± 2.6°C) and COMB (18.9 ± 2.0°C) versus CON (15.3 ± 1.5°C) and FACE (15.8 ± 1.5°C) for heating that was initiated at the beginning of COLD. Tfing was higher ( P < 0.04) during COMB (12.7 ± 5.1°C) versus CON (9.7 ± 2.1°C) and FACE (8.9 ± 2.2°C). The change from BASE for PP (no. of pieces) was less ( P < 0.005) in COMB (−4.5 ± 3.3) and ARM (−5.0 ± 6.0) versus CON (−13.0 ± 7.3) and FACE (−10.0 ± 8.3), and for MAGLOAD, it tended ( P = 0.06) to be less in COMB (−8.9 ± 6.2 cartridges) versus CON (−14.8 ± 3.7 cartridges). There was no change in Sfing from BASE (10.5 kg) to minute 90 in ARM or COMB (0.7 ± 1.4 and −0.2 ± 1.7 kg, respectively) but a decrease ( P < 0.01) in CON and FACE (−2.1 ± 2.0 and −1.6 ± 1.9 kg, respectively). There were no differences in Thand, Tfing, dexterity, and Sfing at minute 90 when comparing heating that was initiated at the beginning of COLD versus delayed heating. In conclusion, heating using either COMB or ARM, compared with CON and FACE, improved Thand and Tfing and reduced the decline in dexterity by 20%–50% and Sfing by 90%. Furthermore, delayed heating had no deleterious effect on Thand, Tfing, dexterity, and Sfing compared with heating that started at the beginning of cold exposure. NEW & NOTEWORTHY The present study demonstrated that, during sedentary cold air exposure, localized heating that was applied from the beginning of cold exposure on the forearm increases hand and finger temperatures and finger strength, leading to subsequent improvements in manual dexterity. In addition, localized heating that was delayed until finger temperatures cooled significantly also caused higher peripheral temperatures, leading to better strength and manual dexterity, compared with no heating.

We examined the influence of 1) prior increase [preheating (PHT)], 2) increase throughout [heating (HT)], and 3) no increase [control (Con)] of body heat content (Hb) on neuromuscular function and manual dexterity of the hands during a 130-min exposure to −20°C (coldEx). Ten volunteers randomly underwent three passive coldEx, incorporating a 10-min moderate-exercise period at the 65th min while wearing a liquid conditioning garment (LCG) and military arctic clothing. In PHT, 50°C water was circulated in the LCG before coldEx until core temperature was increased by 0.5°C. In HT, participants regulated the inlet LCG water temperature throughout coldEx to subjective comfort, while the LCG was not operating in Con. Thermal comfort, rectal temperature, mean skin temperature, mean finger temperature (T̄fing), change in Hb (ΔHb), rate of body heat storage, Purdue pegboard test, finger tapping, handgrip, maximum voluntary contraction, and evoked twitch force of the first dorsal interosseus muscle were recorded. Results demonstrated that, unlike in HT and PHT, thermal comfort, rectal temperature, mean skin temperature, twitch force, maximum voluntary contraction, and finger tapping declined significantly in Con. In contrast, T̄fing and Purdue pegboard test remained constant only in HT. Generalized estimating equations demonstrated that ΔHb and T̄fing were associated over time with hand function, whereas no significant association was detected for rate of body heat storage. It is concluded that increasing Hb not only throughout but also before a coldEx is effective in maintaining hand function. In addition, we found that the best indicator of hand function is ΔHb followed by T̄fing.

For good sleepers, distal skin temperatures (e.g., hands and feet) have been shown to increase when sleep is attempted. This process is said to reflect the body’s action to lose heat from the core via the periphery. However, little is known regarding whether the same process occurs for insomniacs. It would be expected that insomniacs would have restricted heat loss due to anxiety when attempting sleep. The present study compared the finger skin temperature changes when sleep was attempted for 11 chronic primary insomniacs [mean age = 40.0 years (SD 13.3)] and 8 good sleepers [mean age = 38.6 years (SD 13.2)] in a 26-h constant routine protocol with the inclusion of multiple-sleep latency tests. Contrary to predictions, insomniacs demonstrated increases in finger skin temperature when attempting sleep that were significantly greater than those in good sleepers ( P = 0.001), even though there was no significant differences in baseline finger temperature ( P = 0.25). These significant increases occurred despite insomniacs reporting significantly greater sleep anticipatory anxiety ( P < 0.0008). Interestingly, the core body temperature mesor of insomniacs (37.0 ± 0.2°C) was significantly higher than good sleepers (36.8 ± 0.2°C; P = 0.03). Whether insomniacs could have impaired heat loss that is masked by elevated heat production is discussed.

Skin temperature of one finger was measured before and after immersion of the gloved fingers of both hands in 16 degrees C water for 5 min [room temperature (Ta) 24 or 20 degrees C]. At Ta 24 degrees C, 23 of 25 normal nonsmokers (92%) had finger rewarming to above 24 degrees C in 12 min after cold immersion, at Ta 20 degrees C, only 1 of 12 (8%) had similar rewarming. Among 12 habitual smokers only 4 (33%) rewarmed above 24 degrees C (Ta 24 degrees C) following a 1-h abstinence from smoking, but 8 (67%) did so after a 24-h abstinence. Only 2 of these 8, however, did so in a retest 10 min after smoking a cigarette. The smokers were not tested at Ta 20 degrees C. We conclude that air temperature and cigarette smoking are important determinants of finger rewarming following a finger-cooling test.

The effect of exposure to cold on cold-induced vasodilation (CIVD) was examined in military personnel who had experienced a 2-wk stay in the Artic. During this time, the daily regimen consisted of long marches over difficult terrain and sleep in unheated tents with diurnal temperatures ranging from -10 to -40 degrees C. In tests conducted before and after the 2-wk period, CIVD was measured in the left middle finger of each subject by its immersion in ice water. After the 2-wk period, the value of mean finger temperature during the test had decreased relative to that observed before the test, the time required before the first vasodilative temperature increase occurred had become greater, and the finger temperature value at which the vasodilative increase was initiated has been lowered. These changes manifest a deleterious effect of cold exposure on the CIVD, contrary to expectations, and suggest that the effect of short-term cold exposure is to produce a general rather than peripheral acclimation in these subjects.