Swim performance and thermoregulatory effects of wearing clothing in a simulated cold-water survival situation

PURPOSE

Accidental cold-water immersion (CWI) impairs swim performance, increases drowning risk and often occurs whilst clothed. The impact of clothing on thermoregulation and swim performance during CWI was explored with the view of making recommendations on whether swimming is viable for self-rescue; contrary to the traditional recommendations.

METHOD

Ten unhabituated males (age 24 (4) years; height 1.80 (0.08) m; mass 78.50 (10.93) kg; body composition 14.8 (3.4) fat %) completed four separate CWIs in 12 °C water. They either rested clothed or naked (i.e. wearing a bathing costume) or swum self-paced clothed or naked for up to 1 h. Swim speed, distance covered, oxygen consumption and thermal responses (rectal temperature (T re), mean skin temperature (T msk) and mean body temperature T b) were measured.

RESULTS

When clothed, participants swum at a slower pace and for a significantly shorter distance (815 (482) m, 39 (19) min) compared to when naked (1264 (564) m, 52 (18) min), but had a similar oxygen consumption indicating clothing made them less efficient. Swimming accelerated the rate of T msk and T b cooling and wearing clothing partially attenuated this drop. The impairment to swimming performance caused by clothing was greater than the thermal benefit it provided; participants withdrew due to exhaustion before hypothermia developed.

CONCLUSION

Swimming is a viable self-rescue method in 12 °C water, however, clothing impairs swimming capability. Self-rescue swimming could be considered before clinical hypothermia sets in for the majority of individuals. These suggestions must be tested for the wider population.

Cold Stress Effects on Exposure Tolerance and Exercise Performance

Cold weather can have deleterious effects on health, tolerance, and performance. This paper will review the physiological responses and external factors that impact cold tolerance and physical performance. Tolerance is defined as the ability to withstand cold stress with minimal changes in physiological strain. Physiological and pathophysiological responses to short-term (cold shock) and long-term cold water and air exposure are presented. Factors (habituation, anthropometry, sex, race, and fitness) that influence cold tolerance are also reviewed. The impact of cold exposure on physical performance, especially aerobic performance, has not been thoroughly studied. The few studies that have been done suggest that aerobic performance is degraded in cold environments. Potential physiological mechanisms (decreases in deep body and muscle temperature, cardiovascular, and metabolism) are discussed. Likewise, strength and power are also degraded during cold exposure, primarily through a decline in muscle temperature. The review also discusses the concept of thermoregulatory fatigue, a reduction in the thermal effector responses of shivering and vasoconstriction, as a result of multistressor factors, including exhaustive exercise.

Thermal comfort following immersion

Unlike thermal comfort in air, little research has been undertaken exploring thermal comfort around water sports. We investigated the impact of swimming and cooling in air after swimming on thermal comfort. After 10 min of swimming-and-resting cycles in 28°C water, volunteers wearing two types of garments or in swim briefs, faced winds in 24°C air, at rest or when stepping. Thermal comfort was significantly higher during swimming than resting. Post-immersion, following maximum discomfort, in 45 of 65 tests thermal comfort improved although mean skin temperature was still cooling (0.26 [SD 0.19] °C·min(-1) - max was 0.89°C·min(-1)). When thermal comfort was re-established mean skin temperature was lower than at maximal discomfort in 39 of 54 tests (0.81 [SD 0.58] °C - max difference was 2.68°C). The reduction in thermal discomfort in this scenario could be due to the adaptation of thermoreceptors, or to reductions in cooling rates to levels where discomfort was less stimulated. The relief from the recent discomfort may explain why, later, thermal comfort returned to initial levels in spite of poorer thermal profiles.

The relationship between radiant heat, air temperature and thermal comfort at rest and exercise

The aims of the present work were to investigate the relationships between radiant heat load, air velocity and body temperatures with or without coincidental exercise to determine the physiological mechanisms that drive thermal comfort and thermoregulatory behaviour. Seven male volunteers wearing swimming trunks in 18°C, 22°C or 26°C air were exposed to increasing air velocities up to 3 m s(-1) and self-adjusted the intensity of the direct radiant heat received on the front of the body to just maintain overall thermal comfort, at rest or when cycling (60 W, 60 rpm). During the 30 min of the experiments, skin and rectal temperatures were continuously recorded. We hypothesized that mean body temperature should be maintained stable and the intensity of the radiant heat and the mean skin temperatures would be lower when cycling. In all conditions, mean body temperature was lower when facing winds of 3 m s(-1) than during the first 5 min, without wind. When facing winds, in all but the 26°C air, the radiant heat was statistically higher at rest than when exercising. In 26°C air mean skin temperature was lower at rest than when exercising. No other significant difference was observed. In all air temperatures, high correlation coefficients were observed between the air velocity and the radiant heat load. Other factors that we did not measure may have contributed to the constant overall thermal comfort status despite dropping mean skin and body temperatures. It is suggested that the allowance to behaviourally adjust the thermal environment increases the tolerance of cold discomfort.

Biomechanical and physiological demands of kitesurfing and epidemiology of injury among kitesurfers

Kitesurfing is a relatively new extreme water sport that is considered a high-risk sport and has rising popularity. Kitesurfing combines aspects of several water sports, including surfing, windsurfing, and wakeboarding. With a large controllable kite and a small board, kitesurfers travel over the water surface with speeds of up to 35 knots. The vertical lift of the kite makes it possible to perform jumps up to 15 m high and 30 m long, while doing different manoeuvres in the air. Few scientific data are available concerning the biomechanical and physiological demands of kitesurfing and the epidemiology of kitesurfing injury, and research methods used are often questionable. During kitesurfing, considerable stress is placed on the musculoskeletal and physiological systems, and the possibility of injury or fatality is an inherent part of participation. The lower back and thigh muscles are often perceived as being highly stressed, while abdominal muscles, knees, and feet are common sites of pain or discomfort. During kitesurfing, both aerobic and anaerobic metabolism contribute to energy delivery. It is reported in the literature that kitesurfing injuries are mainly acute, due to accidents or trauma. Non-competitive kitesurfing resulted in an overall injury rate of 5.9-7.0 injuries per 1,000 kitesurfing hours. It seems that the risk of injury increases dramatically in competitive kitesurfing. However, contradictory results have been found. Lower extremities were the most common major site of injuries, followed by upper extremities, trunk, and head. Most accidents during kitesurfing reported in the literature were attributed to the inability to detach the kite from the harness. Due to technical innovations, recent studies report uncontrolled actions and unsuccessful tricks and jumps with poor landings as the main mechanisms of injuries. The main purpose of the present paper is to critically analyse the current relevant scientific literature on the biomechanical and physiological demands of kitesurfing and the epidemiology of injury among kitesurfers, in order to obtain greater insights into (i) the stresses imposed on the musculoskeletal and physiological systems by kitesurfing, and (ii) the rate, pattern, and mechanisms of kitesurfing injuries.

Inherent work suit buoyancy distribution: effects on lifejacket self-righting performance

INTRODUCTION

Accidental immersion in cold water is an occupational risk. Work suits and life jackets (LJ) should work effectively in combination to keep the airway clear of the water (freeboard) and enable self-righting. We hypothesized that inherent buoyancy, in the suit or LJ, would be beneficial for enabling freeboard, but its distribution may influence LJ self-righting.

METHODS

Six participants consented to complete nine immersions. Suits and LJ tested were: flotation suit (FLOAT; 85 N inherent buoyancy); oilskins 1 (OS-1) and 2 (OS-2), both with no inherent buoyancy; LJs (inherent buoyancy/buoyancy after inflation/total buoyancy), LJ-1 50/150/200 N, LJ-2 0/290/290 N, LJ-3 80/190/270 N. Once dressed, the subject entered an immersion pool where uninflated freeboard, self-righting performance, and inflated freeboard were measured. Data were compared using Friedman's test to the 0.05 alpha level.

RESULTS

All suits and LJs enabled uninflated and inflated freeboard, but differences were seen between the suits and LJs. Self-righting was achieved on 43 of 54 occasions, irrespective of suit or LJ. On all occasions that self-righting was not achieved, this occurred in an LJ that included inherent buoyancy (11/54 occasions). Of these 11 failures, 8 occurred (73% of occasions) when the FLOAT suit was being worn.

DISCUSSION

LJs that included inherent buoyancy, that are certified as effective on their own, worked less effectively from the perspective of self-righting in combination with a work suit that also included inherent buoyancy. Equipment that is approved for use in the workplace should be tested in combination to ensure adequate performance in an emergency scenario.

The effect of ethnicity on the vascular responses to cold exposure of the extremities

PURPOSE

Cold injuries are more prevalent in individuals of African descent (AFD). Therefore, we investigated the effect of extremity cooling on skin blood flow (SkBF) and temperature (T sk) between ethnic groups.

METHODS

Thirty males [10 Caucasian (CAU), 10 Asian (ASN), 10 AFD] undertook three tests in 30 °C air whilst digit T sk and SkBF were measured: (i) vasomotor threshold (VT) test--arm immersed in 35 °C water progressively cooled to 10 °C and rewarmed to 35 °C to identify vasoconstriction and vasodilatation; (ii) cold-induced vasodilatation (CIVD) test--hand immersed in 8 °C water for 30 min followed by spontaneous warming; (iii) cold sensitivity (CS) test--foot immersed in 15 °C water for 2 min followed by spontaneous warming. Cold sensory thresholds of the forearm and finger were also assessed.

RESULTS

In the VT test, vasoconstriction and vasodilatation occurred at a warmer finger T sk in AFD during cooling [21.2 (4.4) vs. 17.0 (3.1) °C, P = 0.034] and warming [22.0 (7.9) vs. 12.1 (4.1) °C, P = 0.002] compared with CAU. In the CIVD test, average SkBF during immersion was greater in CAU [42 (24) %] than ASN [25 (8) %, P = 0.036] and AFD [24 (13) %, P = 0.023]. Following immersion, SkBF was higher and rewarming faster in CAU [3.2 (0.4) °C min(-1)] compared with AFD [2.5 (0.7) °C min(-1), P = 0.037], but neither group differed from ASN [3.0 (0.6) °C min(-1)]. Responses to the CS test and cold sensory thresholds were similar between groups.

CONCLUSION

AFD experienced a more intense protracted finger vasoconstriction than CAU during hand immersion, whilst ASN experienced an intermediate response. This greater sensitivity to cold may explain why AFD are more susceptible to cold injuries.

Moving in extreme environments: what's extreme and who decides?

Humans work, rest and play in immensely varied extreme environments. The term 'extreme' typically refers to insufficiency or excess of one or more stressors, such as thermal energy or gravity. Individuals' behavioural and physiological capacity to endure and enjoy such environments varies immensely. Adverse effects of acute exposure to these environments are readily identifiable (e.g. heat stroke or bone fracture), whereas adverse effects of chronic exposure (e.g. stress fractures or osteoporosis) may be as important but much less discernable. Modern societies have increasingly sought to protect people from such stressors and, in that way, minimise their adverse effects. Regulations are thus established, and advice is provided on what is 'acceptable' exposure. Examples include work/rest cycles in the heat, hydration regimes, rates of ascent to and duration of stay at altitude and diving depth. While usually valuable and well intentioned, it is important to realise the breadth and importance of limitations associated with such guidelines. Regulations and advisories leave less room for self-determination, learning and perhaps adaptation. Regulations based on stress (e.g. work/rest cycles relative to WBGT) are more practical but less direct than those based on strain (e.g. core temperature), but even the latter can be substantively limited (e.g. by lack of criterion validation and allowance for behavioural regulation in the research on which they are based). Extreme Physiology & Medicine is publishing a series of reviews aimed at critically examining the issues involved with self- versus regulation-controlled human movement acutely and chronically in extreme environments. These papers, arising from a research symposium in 2013, are about the impact of people engaging in such environments and the effect of rules and guidelines on their safety, enjoyment, autonomy and productivity. The reviews will cover occupational heat stress, sporting heat stress, hydration, diving, extreme loading, chronic unloading and high altitude. Ramifications include factors such as health and safety, productivity, enjoyment and autonomy, acute and chronic protection and optimising adaptation.

Physiological cost and thermal envelope: a novel approach to cycle garment evaluation during a representative protocol

This study aimed to examine thermoregulation in different clothing assemblies during a representative cycling exercise protocol. Six men undertook cycling exercise simulating representative thermal exchange challenges while wearing low (LOW), intermediate (INT1 and INT2), or high (HI) amounts of clothing. Exercise was conducted at 14.5 °C, 46.8% relative humidity and included a "flat" [45 min at 35% peak power output (PPO), wind speed 8.3 m/s], "uphill" (30 min at 55% PPO, wind speed 3.6 m/s), and "downhill" (20 min at 50 W, wind speed 16.7 m/s) stage. Rectal temperature changed with the exercise stage and was independent of clothing assembly. In contrast, an "envelope" was evident for mean body temperature, resulting from differences in mean skin temperature between the LOW and HI conditions. The elevated mean body temperature in HI was associated with increased physiological "cost," in the form of increased sweat production and heart rate. Physiological cost provides a better index of clothing performance than deep body temperature in the "thermoregulatory zone," as a consequence sports clothing should attempt to optimize the balance between comfort and reduced physiological cost.

Thermal perceptions and skin temperatures during continuous and intermittent ventilation of the torso throughout and after exercise in the heat

OBJECTIVE

This study tested the hypothesis that intermittent cooling in air-perfused vests (APV) will not only maintain thermal balance but, due to cyclical activations of cutaneous thermoreceptors, also enhance thermal perceptions.

METHOD

Ten physically active males completed four conditions where they exercised (walking: 5 km h(-1), 2 % gradient) in a hot environment (~34.0 °C, 50 % RH) for 72 min, followed by a 33-min period of rest. They wore an APV throughout. The four conditions differed in respect to the profile of ambient air that was perfused through the APV: continuous perfusion (CP); intermittent perfusion of 6 min ON/OFF periods (IPonoff); a steady increase and decrease in flow rate in equal increments (IPramp); and an initial step-increase in the flow rate followed by an incremental decrease to zero flow rate (IPtriang). Whole body and torso thermal comfort (TC, TTC), whole body and torso temperature sensation (TS, TTS), whole body and torso skin temperature ([Formula: see text], [Formula: see text]), local relative humidity ([Formula: see text]) and rectal temperature (T re) were measured.

RESULTS

There were no significant differences in T re, absolute whole body and local [Formula: see text], TC, TTC and TS between the cooling profiles. However, TTS was cooler in CP and IPramp than IPonoff and IPtriang. Even though intermittent cooling did not significantly enhance thermal perceptions in CP, a trend existed for TC (P = 0.063) to become less favourable over time.

CONCLUSION

To reduce the power consumption and extend the battery life of an APV, it is recommended that an intermittent cooling profile should be adopted.

A report on the first conference on physiological and physical employment standards, Canberra, Australia November 27 to 28, 2012

This is a report of the First Conference on Physiological and Physical Employment Standards. This was the first conference of its kind, attended by scientists, physicians, occupational medics, high-ranking politicians and military personal from ten nations.

Cold sensitivity test for individuals with non-freezing cold injury: the effect of prior exercise

BACKGROUND

One of the chronic symptoms of non-freezing cold injury (NFCI) is cold sensitivity. This study examined the effects of prior exercise on the response to a cold sensitivity test (CST) in NFCI patients with the aim of improving diagnostic accuracy.

METHODS

Twenty three participants, previously diagnosed with NFCI by a Cold Injuries Clinic, undertook two CSTs. Participants either rested (air temperature 31°C) for approximately 80 min (prior rest condition (REST)) or rested for 30 min before exercising gently for 12 min (prior exercise condition (EX)). Following REST and EX, the participants placed their injured foot, covered in a plastic bag, into 15°C water for 2 min; this was followed by spontaneous rewarming in 31°C air for 10 min.

RESULTS

The great toe skin temperature (Tsk) before immersion averaged 32.5 (3.4)°C in both conditions. Following immersion, the rate of rewarming of the great toe Tsk was faster in EX compared to REST and was higher 5 min (31.7 (3.4)°C vs. 29.8 (3.4)°C) and 10 min (33.8 (4.0)°C vs. 32.0 (4.0)°C) post-immersion. Over the first 5 min of rewarming, changes in the great toe Tsk correlated with the changes in skin blood flow (SkBF) in EX but not the REST condition. No relationship was observed between Tsk in either CST and the severity of NFCI as independently clinically assessed.

CONCLUSIONS

Exercise prior to the CST increased the rate of the toe Tsk rewarming, and this correlated with the changes in SkBF. However, the CST cannot be used in isolation in the diagnosis of NFCI, although the EX CST may prove useful in assessing the severity of post-injury cold sensitivity for prognostic and medico-legal purposes.