Acute effects of normobaric hypoxia on hand-temperature responses during and after local cold stress

The impact of cold, hypoxia, and physical exertion on pistol accuracy and tactical performance

The purpose of this study was to examine the impact of independent cold and combined cold and hypoxic exposures on operational-specific task performance including pistol marksmanship, pistol magazine reload ability, and subjective and objective thermal indices before and after a whole-body physical exertional task. Twelve participants were exposed to Thermoneutral Normoxic (24 °C; FiO2 21%), Cold Normoxic (10 °C; FiO2 21%), and Cold Hypoxic (10 °C; FiO2 14%) conditions for 30min before performing pistol marksmanship at distances of 6.40 and 13.72m and a pistol magazine reload task before and after 3 sets of sandbag deadlifts at 50% body mass. Thermal perception and hand temperatures were collected before and after the physical exertion task. There were no significant differences in Pistol Accuracy performance at distances of 6.40 and 13.72m due to physical exertion, cold, or hypoxia. Following physical exertion, Pistol Accuracy was similar between Thermoneutral and Cold Normoxic conditions but lead to 17% and a 10% reduction in performance during the Cold Hypoxic condition, compared to Thermoneutral and Cold Normoxic conditions. There was no change in Pistol Accuracy for the Thermoneutral Normoxic condition. The pistol magazine reload task was not impacted by physical exertion, but there was a reduction in performance in Cold Normoxic 21% (4.04s) and Cold Hypoxic 16% (3.08s) conditions. Physical exertion did not impact hand temperature but did increase thermal perception scores for all conditions. These findings indicate that cold exposure reduced both tactical dexterity and pistol marksmanship, however, physical exertion may offset these deficits via an increase in thermal perception. Additionally, hypoxemia was the primary mediator of marksmanship performance in cold hypoxic environments following an acute bout of physical exertion. Thus, in cold mountainous environments, marksmen should be aware of their elevation and utilize brief episodes of physical activity to enhance their thermal state when marksmanship is a priority for operational success.

Infrared Thermography as a Non-Invasive Tool in Musculoskeletal Disease Rehabilitation—The Control Variables in Applicability—A Systematic Review

In recent years, the usefulness of infrared thermography (IRT) as a valuable supplementary imaging method in medical diagnostics, as well as for assessing the effects of the treatment of musculoskeletal injuries, has been increasingly confirmed. At the same time, great importance is attached to the standards of thermographic research, the fulfillment of which determines the correct methodology and interpretation of the results. This article discusses the medical applications of infrared thermography in musculoskeletal system diseases, with particular emphasis on its usefulness in assessing the therapeutic effects of physical treatments used in rehabilitation. The literature from the last decade that is available in the Medline and Web of Science databases has been reviewed. Among the physiotherapeutic methods used, the following were selected that directly affect the musculoskeletal system: cryotherapy, laser therapy, electrotherapy, diathermy, and massage. The article summarizes all the guidelines and recommendations for IR imaging in medicine and rehabilitation.

Effect of fatigue strength exercise on anterior thigh skin temperature rewarming after cold stress test

Although dynamic thermography skin temperature assessment has been used in medical field, scientific evidence in sports is scarce. The aim of the study was to assess changes in anterior thigh skin temperature in response to a cold stress test after a strength exercise fatiguing protocol. Ten physically active adults performed a familiarization session and two strength exercise sessions, one with dominant and the other with non-dominant lower limb. Participants performed bouts of 10 concentric and eccentric contractions of leg extensions in an isokinetic device until reaching around 30% of force loss. Infrared thermographic images were taken at baseline conditions and after the fatigue level from both thighs after being cooled using a cryotherapy system. ROIs included vastus medialis, rectus femoris, adductor and vastus lateralis. Skin temperature rewarming was assessed during 180s after the cooling process obtaining the coefficients of the following equation: ΔSkin temperature = β₀ + β_{1 *} ln(T), being β₀ and β₁ the constant and slope coefficients, respectively, T the time elapsed following the cold stress in seconds, and ΔSkin temperature the difference between the skin temperature at T respect and the pre-cooling moment. Lower β₀ and higher β₁ were found for vastus lateralis and rectus femoris in the intervention lower limb compared with baseline conditions (p < 0.05 and ES > 0.6). Adductor only showed differences in β₀ (p = 0.01 and ES = 0.92). The regressions models obtained showed that β₀ and β₁ had a direct relationship with age and muscle mass, but an inverse relationship with the number of series performed until 30% of fatigue (R² = 0.8). In conclusion, fatigue strength exercise results in a lower skin temperature and a faster thermal increase after a cold stress test.

Reproducibility of Skin Temperature Response after Cold Stress Test Using the Game Ready System: Preliminary Study

The objective of this preliminary study was to determine the reproducibility of lower limbs skin temperature after cold stress test using the Game Ready system. Skin temperature of fourteen participants was measured before and after cold stress test using the Game Ready system and it was repeated the protocol in four times: at 9:00, at 11:00, at 19:00, and at 9:00 h of the posterior day. To assess skin temperature recovery after cold stress test, a logarithmic equation for each region was calculated, and constant (β₀) and slope (β₁) coefficients were obtained. Intraclass correlation coefficient (ICC), standard error (SE), and within-subject coefficient of variation (CV) were determined. No differences were observed between measurement times in any of the regions for the logarithmic coefficients (p > 0.38). Anterior thigh (β₀ ICC 0.33–0.47; β₁ ICC 0.31–0.43) and posterior knee (β₀ ICC 0.42–0.58; β₁ ICC 0.28–0.57) were the regions with the lower ICCs, and the other regions presented values with a fair and good reproducibility (ICC > 0.41). Posterior leg was the region with the better reproducibility (β₀ ICC 0.68–0.78; β₁ ICC 0.59–0.74; SE 3–4%; within-subject CV 7–12%). In conclusion, cold stress test using Game Ready system showed a fair and good reproducibility, especially when the posterior leg was the region assessed.

Human cold habituation: Physiology, timeline, and modifiers

Habituation is an adaptation seen in many organisms, defined by a reduction in the response to repeated stimuli. Evolutionarily, habituation is thought to benefit the organism by allowing conservation of metabolic resources otherwise spent on sub-lethal provocations including repeated cold exposure. Hypermetabolic and/or insulative adaptations may occur after prolonged and severe cold exposures, resulting in enhanced cold defense mechanisms such as increased thermogenesis and peripheral vasoconstriction, respectively. Habituation occurs prior to these adaptations in response to short duration mild cold exposures, and, perhaps counterintuitively, elicits a reduction in cold defense mechanisms demonstrated through higher skin temperatures, attenuated shivering, and reduced cold sensations. These habituated responses likely serve to preserve peripheral tissue temperature and conserve energy during non-life threatening cold stress. The purpose of this review is to define habituation in general terms, present evidence for the response in non-human species, and provide an up-to-date, critical examination of past studies and the potential physiological mechanisms underlying human cold habituation. Our aim is to stimulate interest in this area of study and promote further experiments to understand this physiological adaptation.

Independent and combined impact of hypoxia and acute inorganic nitrate ingestion on thermoregulatory responses to the cold

Purpose

This study assessed the impact of normobaric hypoxia and acute nitrate ingestion on shivering thermogenesis, cutaneous vascular control, and thermometrics in response to cold stress.

Method

Eleven male volunteers underwent passive cooling at 10 °C air temperature across four conditions: (1) normoxia with placebo ingestion, (2) hypoxia (0.130 F_iO₂) with placebo ingestion, (3) normoxia with 13 mmol nitrate ingestion, and (4) hypoxia with nitrate ingestion. Physiological metrics were assessed as a rate of change over 45 min to determine heat loss, and at the point of shivering onset to determine the thermogenic thermoeffector threshold.

Result

Independently, hypoxia expedited shivering onset time (p = 0.05) due to a faster cooling rate as opposed to a change in central thermoeffector thresholds. Specifically, compared to normoxia, hypoxia increased skin blood flow (p = 0.02), leading to an increased core-cooling rate (p = 0.04) and delta change in rectal temperature (p = 0.03) over 45 min, yet the same rectal temperature at shivering onset (p = 0.9). Independently, nitrate ingestion delayed shivering onset time (p = 0.01), mediated by a change in central thermoeffector thresholds, independent of changes in peripheral heat exchange. Specifically, compared to placebo ingestion, no difference was observed in skin blood flow (p = 0.5), core-cooling rate (p = 0.5), or delta change in rectal temperature (p = 0.7) over 45 min, while nitrate reduced rectal temperature at shivering onset (p = 0.04). No interaction was observed between hypoxia and nitrate ingestion.

Conclusion

These data improve our understanding of how hypoxia and nitric oxide modulate cold thermoregulation.

Combined stimuli of cold, hypoxia, and dehydration status on body temperature in rats: a pilot study with practical implications for humans

OBJECTIVE

As human thermoregulatory responses to maintain core body temperature (T_core) under multiple stressors such as cold, hypoxia, and dehydration (e.g., exposure to high-altitude) are varied, the combined effects of cold, hypoxia, and dehydration status on T_core in rats were investigated. The following environmental conditions were constructed: (1) thermoneutral (24 °C) or cold (10 °C), (2) normoxia (21% O₂) or hypoxia (12% O₂), and (3) euhydration or dehydration (48 h water deprivation), resulted in eight environmental conditions [2 ambient temperatures (T_a) × 2 oxygen levels × 2 hydration statuses)]. Each condition lasted for 24 h.

RESULTS

Normoxic conditions irrespective of hypoxia or dehydration did not strongly decrease the area under the curve (AUC) in T_core during the 24 period, whereas, hypoxic conditions caused greater decreases in the AUC in T_core, which was accentuated with cold and dehydration (T_a × O₂ × hydration, P = 0.040 by three-way ANOVA). In contrast, multiple stressors (T_a × O₂ × hydration or T_a × O₂ or O₂ × hydration or T_a × hydration) did not affect locomotor activity counts (all P > 0.05), but a significant simple main effect for O₂ and T_a was observed (P < 0.001). Heat loss index was not affected by all environmental conditions (all P > 0.05). In conclusion, decreases in T_core were most affected by multiple environmental stressors such as cold, hypoxia, and dehydration.

Topical Nifedipine Administration for Secondary Prevention in Frostbitten Patients

Frostbite is a cold-related injury with a growing incidence among healthy subjects. Sequelae after frostbite are frequent and vary among individuals. Here, we studied the thermal response in the digits of hands and feet of five subjects who had recovered from previous frostbite, except for their lasting sequelae. We considered three different conditions: digits unaffected by frostbite nor sequelae (healthy), those affected but which did not suffer amputation (frostbitten without amputation), and the remainder/stumps of digits that underwent partial amputation (frostbitten with amputation). Three consecutive immersions in cold water (8°C; 3 min) interspersed by 1 minute of thermal recovery were performed. After 30 min, a topical 10% nifedipine preparation was applied to hands and feet, and the same cold exposure protocol to evaluate its effect was followed. In basal condition and immediately after each immersion, the temperature of individual digits was assessed using thermography. We observed different thermal responses among the different digits of hands and feet, even without the nifedipine treatment. Nifedipine had a cooling effect on healthy and post-amputated tissue without thermal stress. In cold conditions, topic nifedipine application improved the cold response in healthy fingers but had a negative effect on those from which parts had been amputated. The topical nifedipine had detrimental effects on toes in all conditions. Topical nifedipine can help to the preservation of healthy fingers exposed to cold, with adequate thermal insulation; but it is necessary to remark its potentially harmful effects on previously frostbitten tissue. Because of the differences observed on individual regional response to cold, thermography can be a useful tool in the frostbite prevention for subjects habitually exposed to cold environment.

Interactions of mild hypothermia and hypoxia on finger vasoreactivity to local cold stress

We examined the interactive effects of mild hypothermia and hypoxia on finger vasoreactivity to local cold stress. Eight male lowlanders performed, in a counterbalanced order, a normoxic and a hypoxic (partial pressure of oxygen: ~12 kPa) hand cold provocation (consisting of a 30-min immersion in 8°C water), while immersed to the chest either in 21°C [cold trials; 0.5°C fall in rectal temperature (T_rec) from individual preimmersion values], or in 35.5°C water, or while exposed to 27°C air. The duration of the trials was kept constant in each breathing condition. Physiological (T_rec, skin temperature, cutaneous vascular conductance, oxygen uptake) and perceptual (thermal sensation and comfort, local pain, affective valence) reactions were monitored continually. Hypoxia accelerated the drop in T_rec by ~14 min (P = 0.06, d = 0.67). In the air-exposure trials, hypoxia did not alter finger perfusion during the local cooling, whereas it impaired the finger rewarming response following the cooling (P < 0.01). During the 35.5°C immersion, the finger vasomotor tone was enhanced, especially in hypoxia (P = 0.01). Mild hypothermia aggravated finger vasoconstriction instigated by local cooling (P < 0.01), but the response did not differ between the two breathing conditions (P > 0.05). Hypoxia tended to attenuate the sensation of coldness (P = 0.10, r = 0.40) and thermal discomfort (P = 0.09, r = 0.46) in the immersed hand. Both in normoxia and hypoxia, the whole body thermal state dictates the cutaneous vasomotor reactivity to localized cold stimulus.

Cold-induced vasodilation responses before and after exercise in normobaric normoxia and hypoxia

PURPOSE

Cold-induced vasodilation (CIVD) is known to protect humans against local cold injuries and improve manual dexterity. The current study examined the effects of metabolic heat production on cold-induced vasodilation responses in normobaric hypoxia and normoxia.

METHODS

Ten participants immersed their non-dominant hand into 5 °C water for 15 min. Minimum finger temperature (T_min), maximum finger temperature (T_max), onset time, amplitude, and peak time were measured before and after exercise under normoxia (21% O₂) and two levels of normobaric hypoxia (17% O₂ and 13% O₂).

RESULTS

Neither T_min nor amplitude was affected by hypoxia. However, T_max was significantly decreased by hypoxia while reduction in onset time and peak time trended towards significance. T_min, T_max, and amplitude were significantly higher during post-exercise CIVD than pre-exercise CIVD.

CONCLUSION

The CIVD response may be negatively affected by the introduction of hypoxia whereas metabolic heat production via exercise may counteract adverse effects of hypoxia and improve CIVD responses.

Amputation Risk Factors in Severely Frostbitten Patients

In recent years, the incidence of frostbite has increased among healthy young adults who practice winter sports (skiing, mountaineering, ice climbing and technical climbing/alpinism) at both the professional and amateur levels. Moreover, given that the population most frequently affected is healthy and active, frostbite supposes a substantial interruption of their normal activity and in most cases is associated with long-term sequelae. It particularly has a higher impact when the affected person’s daily activities require exposure to cold environments, as either sports practices or work activities in which low temperatures are a constant (ski patrols, mountain guides, avalanche forecasters, workers in the cold chain, etc.). Clinical experience with humans shows a limited reversibility of injuries via potential tissue regeneration, which can be fostered with optimal medical management. Data were collected from 92 frostbitten patients in order to evaluate factors that represent a risk of amputation after severe frostbite. Mountain range, years of expertise in winter mountaineering, time elapsed before rewarming and especially altitude were the most important factors for a poor prognosis.

The Effect of a 300 mBar Increase in Barometric Pressure on Digital Microcirculation in Healthy Subjects Exposed to High Altitude: Is the Use of a Portable Hyperbaric Chamber to Treat Frostbite and/or Hypothermia in the Field Indicated? (Flow_Pulse Study)

INTRODUCTION

Hypothermia and frostbite occur when there is a significant decrease in central and peripheral body temperature in individuals exposed to cold windy conditions, often at high altitude or in a mountain environment. Portable hyperbaric chambers increase the barometric pressure and thereby the partial pressure of oxygen inside the chamber, and their use is a well-known treatment for altitude illness. This study aims to show that a portable hyperbaric chamber could also be used to treat hypothermia and frostbite in the field, when rescue or descent is impossible or delayed.

METHODS

During a European research program (SOS-MAM, Flow Pulse study) measurements were taken from 27 healthy nonacclimatized voluntary subjects (21 men, 6 women, mean age 41 ± 17) at an altitude of 3800 m (Chamonix Mountain Lab, Aiguille du Midi, France) right before and immediately after spending 1 hour in a portable hyperbaric chamber at 300 mbar. We measured digital cutaneous temperature (Tcut), digital cutaneous blood flow (Fcut), digital tissue oxygenation (T_cPO₂), blood oxygen saturation (S_pO₂), heart rate, and core temperature. Air temperature inside the chamber (Tchamb) was measured throughout the whole session.

RESULTS

We observed significant increases in Tchamb: 9.3°C compared with the outside temperature, Tcut: +7.5°C (±6.2°C 71%), Fcut: +58_PU (±89) (+379%), T_cPO₂: +18 mmHg (±11.9) (304%), and S_pO₂: 13%.

CONCLUSION

This study shows that a portable hyperbaric chamber can be used to treat frostbite and/or hypothermia in the field at altitude when descent or rescue is impossible or even simply delayed.

In Shackleton's trails: Central and local thermoadaptive modifications to cold and hypoxia after a man-hauling expedition on the Antarctic Plateau

Cold and hypoxia constitute the main environmental stressors encountered on the Antarctic Plateau. Hence, we examined whether central and/or peripheral acclimatisation to the combined stressors of cold and hypoxia would be developed in four men following an 11-day man-hauling expedition on this polar region. Before and after the journey, participants performed a static whole-body immersion in 21 °C water, during which they were breathing a hypoxic gas (partial pressure of inspired O₂: ~97 mmHg). To evaluate their local responses to cold, participants also immersed the hand into 8 °C water for 30 min, while they were whole-body immersed and mildly hypothermic [i.e. 0.5 °C fall in rectal temperature (T_rec) from individual pre-immersion values]. T_rec and skin temperature (T_sk), skin blood flux, and oxygen uptake (reflecting shivering thermogenesis) were monitored throughout. The polar expedition accelerated by ~14 min the drop in T_rec [final mean (95% confidence interval) changes in T_rec: Before = -0.94 (0.15) °C, After: - 1.17 (0.23) °C]. The shivering onset threshold [Before: 19 (22) min, After: 25 (19) min] and gain [Before: - 4.19 (3.95) mL min^-1 kg^-1, After: - 1.70 (1.21) mL min^-1 kg^-1] were suppressed by the expedition. T_sk did not differ between trials. The development of a greater post-expedition hypothermic state did not compromise finger circulation during the hand-cooling phase. Present findings indicate therefore that a hypothermic pattern of cold acclimatisation, as investigated in hypoxia, was developed following a short-term expedition on the South Polar Plateau; an adaptive response that is characterised mainly by suppressed shivering thermogenesis, and partly by blunted cutaneous vasoconstriction.

Does Hypoxia Decrease the Metabolic Rate?

In some organisms and cells, oxygen availability influences oxygen consumption. In this review, we examine this phenomenon of hypoxic hypometabolism (HH), discussing its features, mechanisms, and implications. Small mammals and other vertebrate species exhibit "oxyconformism," a downregulation of metabolic rate and body temperature during hypoxia which is sensed by the central nervous system. Smaller body mass and cooler ambient temperature contribute to a high metabolic rate in mammals. It is this hypermetabolic state that is suppressed by hypoxia leading to HH. Larger mammals including humans do not exhibit HH. Tissues and cells also exhibit reductions in respiration during hypoxia in vitro, even at oxygen levels ample for mitochondrial oxidative phosphorylation. The mechanisms of cellular HH involve intracellular oxygen sensors including hypoxia-inducible factors, AMP-activated protein kinase (AMPK), and mitochondrial reactive oxygen species (ROS) which downregulate mitochondrial activity and ATP utilization. HH has a profound impact on cardiovascular, respiratory, and metabolic physiology in rodents. Therefore, caution should be exercised when extrapolating the results of rodent hypoxia studies to human physiology.

No association between hand and foot temperature responses during local cold stress and rewarming

Purpose

The purpose was to examine whether associations exist between temperature responses in the fingers vs. toes and hand vs. foot during local cold-water immersion and rewarming phases.

Methods

Seventy healthy subjects (58 males, 12 females) immersed their right hand or right foot, respectively, in 8 °C water for 30 min (CWI phase), followed by a 15-min spontaneous rewarming (RW) in 25 °C air temperature.

Results

Temperature was lower in the toes than the fingers during the baseline phase (27.8 ± 3.0 vs. 33.9 ± 2.5 °C, p < 0.001), parts of the CWI phase (min 20–30: 8.8 ± 0.7 vs. 9.7 ± 1.4 °C, p < 0.001), and during the RW phase (peak temperature: 22.5 ± 5.1 vs. 32.7 ± 3.6 °C, p < 0.001). Cold-induced vasodilatation (CIVD) was more common in the fingers than in the toes (p < 0.001). Within the first 10 min of CWI, 61% of the subjects exhibited a CIVD response in the fingers, while only 6% of the subjects had a CIVD response in the toes. There was a large variability of temperature responses both within and between extremities, and there was a weak correlation between finger- and toe temperature both during the CWI (r = 0.21, p = 0.08) and the RW phases (r = 0.26, p = 0.03).

Conclusions

Results suggest that there is generally a lower temperature in the toes than the fingers after a short time of local cold exposure and that the thermal responses of the fingers/hands are not readily transferable to the toes/foot.

A New Proposal for Management of Severe Frostbite in the Austere Environment

Despite advances in outdoor clothing and medical management of frostbite, individuals still experience catastrophic amputations. This is a particular risk for those in austere environments, due to resource limitations and delayed definitive treatment. The emerging best therapies for severe frostbite are thrombolytics and iloprost. However, they must be started within 24 hours after rewarming for recombinant tissue plasminogen activator (rt-PA) and within 48 hours for iloprost. Evacuation of individuals experiencing frostbite from remote environments within 24 to 48 hours is often impossible. To date, use of these agents has been confined to hospitals, thus depriving most individuals in the austere environment of the best treatment. We propose that thrombolytics and iloprost be considered for field treatment to maximize chances for recovery and reduce amputations. Given the small but potentially serious risk of complications, rt-PA should only be used for grade 4 frostbite where amputation is inevitable, and within 24 hours of rewarming. Prostacyclin has less risk and can be used for grades 2 to 4 frostbite within 48 hours of rewarming. Until more field experience is reported with these agents, their use should probably be restricted to experienced physicians. Other modalities, such as local nerve blocks and improving oxygenation at high altitude may also be considered. We submit that it remains possible to improve frostbite outcomes despite delayed evacuation using resource-limited treatment strategies. We present 2 cases of frostbite treated with rt-PA at K2 basecamp to illustrate feasibility and important considerations.

The effect of a Live-high Train-high exercise regimen on behavioural temperature regulation

PURPOSE

Acute hypoxia alters the threshold for sensation of cutaneous thermal stimuli. We hypothesised that hypoxia-induced alterations in cutaneous temperature sensation may lead to modulation of the perception of temperature, ultimately influencing behavioural thermoregulation and that the magnitude of this effect could be influenced by daily physical training.

METHODS

Fourteen men were confined 10 days to a normobaric hypoxic environment (P_IO₂ = 88.2 ± 0.6 mmHg, corresponding to 4175 m elevation). Subjects were randomly assigned to a non-exercising (Live-high, LH, N = 6), or exercising group (Live-high Train-high, LH-TH, N = 8) comprised of 1-h bouts of cycle ergometry, twice daily, at a work-rate equivalent to 50% hypoxic peak power output. A subset of subjects (N = 5) also completed a control trial under normoxic conditions. The thermal comfort zone (TCZ) was determined in normoxia, and during hypoxic confinement days 2 (HC2) and 10 (HC10) in both groups using a water-perfused suit in which water temperature was regulated by the subjects within a range, they deemed thermally comfortable. Mean skin temperature and proximal-distal temperature gradients (two sites: forearm-fingertip, calf-toe) were recorded each minute throughout the 60-min protocol.

RESULTS

The average width of the TCZ did not differ between the control group (9.0 ± 6.9 °C), and the LH and LH-TH groups on days HC2 (7.2 ± 4.2 °C) and HC10 (10.2 ± 7.5 °C) of the hypoxic exposure (p = 0.256). [Formula: see text] was marginally higher on HC2 (35.9 ± 1.0 °C) compared to control (34.9 ± 0.8 °C, p = 0.040), but not on HC10 (35.6 ± 1.0 °C), reflecting the responses of hand perfusion.

CONCLUSION

There was a little systematic effect of hypoxia or exercise training on TCZ magnitude or boundary temperatures.

Effects of Two Short-Term, Intermittent Hypoxic Training Protocols on the Finger Temperature Response to Local Cold Stress

The study examined the effects of two short-term, intermittent hypoxic training protocols, namely exercising in hypoxia and living in normoxia (LL-TH; n=8), and exercising in normoxia preceded by a series of brief intermittent hypoxic exposures at rest (IHE+NOR; n=8), on the finger temperature response during a sea-level local cold test. In addition, a normoxic group was assigned as a control group (NOR; n=8). All groups trained on a cycle-ergometer 1 h/day, 5 days/week for 4 weeks at 50% of peak power output. Pre, post, and 11 days after the last training session, subjects immersed their right hand for 30 min in 8°C water. In the NOR group, the average finger temperature was higher in the post (+2.1°C) and 11-day after (+2.6°C) tests than in the pre-test (p≤0.001). Conversely, the fingers were significantly colder immediately after both hypoxic protocols (LL-TH: -1.1°C, IHE+NOR: -1.8°C; p=0.01). The temperature responses returned to the pre-training level 11 days after the hypoxic interventions. Ergo, present findings suggest that short-term intermittent hypoxic training impairs sea-level local cold tolerance; yet, the hypoxic-induced adverse responses seem to be reversible within a period of 11 days.

Responses of the hands and feet to cold exposure

An initial response to whole-body or local exposure of the extremities to cold is a strong vasoconstriction, leading to a rapid decrease in hand and foot temperature. This impairs tactile sensitivity, manual dexterity, and muscle contractile characteristics while increasing pain and sympathetic drive, decreasing gross motor function, occupational performance, and survival. A paradoxical and cyclical vasodilatation often occurs in the fingers, toes, and face, and this has been termed the hunting response or cold-induced vasodilatation (CIVD). Despite being described almost a century ago, the mechanisms of CIVD are still disputed; research in this area has remained largely descriptive in nature. Recent research into CIVD has brought increased standardization of methodology along with new knowledge about the impact of mediating factors such as hypoxia and physical fitness. Increasing mechanistic analysis of CIVD has also emerged along with improved modeling and prediction of CIVD responses. The present review will survey work conducted during this century on CIVD, its potential mechanisms and modeling, and also the broader context of manual function in cold conditions.