Heather Lunt

‘Cross-adaptation’: habituation to short repeated cold-water immersions affects the response to acute hypoxia in humans

Adaptation to an environmental stressor is usually studied in isolation, yet these stressors are often encountered in combination in the field, an example being cold and hypoxia at altitude. There has been a paucity of research in this area, although work with rodents indicates that habituation to repeated short cold exposures has a cross‐adaptive effect during hypoxia. The present study tested the hypothesis that cross‐adaptation is also possible with humans. Thirty‐two male volunteers were exposed to 10 min bouts of normoxic and hypoxic ( 0.12) rest and exercise (100 W on a recumbent cycle ergometer). These were repeated after a 96 h interval, during which participants completed six, 5 min immersions in either cold (12°C, CW) or thermoneutral water (35°C, TW). Venous blood samples were taken immediately after each bout, for determination of catecholamine concentrations. A three‐lead ECG was recorded throughout and the final 5 min of each bout was analysed for heart rate variability using fast fourier transformations (and displayed as log transformed data (ln)). In comparison with the first hypoxic exercise exposure, the second exposure of the CW group resulted in an increased ln high frequency (ln HF) power (P < 0.001) and reduced adrenaline (P < 0.001) and noradrenaline concentrations (P < 0.001). Adrenaline and noradrenaline concentrations were lower in the CW group during the second hypoxic exercise compared to the TW group (P= 0.042 and P= 0.003), but ln HF was not. When separated into hypoxic sensitive and hypoxic insensitive subgroups, ln HF was higher in the hypoxic sensitive CW group during the second hypoxic exercise than in any of the other subgroups. Cold habituation reduced the sympathetic response (indicated by the reduced catecholamine concentrations) and elevated the parasympathetic activity (increased ln HF power) to hypoxic exercise. These data suggest a generic autonomic cross‐adaptive effect between cold habituation and exposure to acute hypoxia in humans.

Water immersion as a recovery aid from intermittent shuttle running exercise

Abstract Aim: To investigate the effect of different water immersion (WI) treatments on recovery from intermittent shuttle running exercise in comparison to an ecologically relevant control. Methods: Forty males performed 90 minutes intermittent shuttle running, following which they were assigned to either: (1) 12-min standing WI at 12°C; (2) 12-min standing WI at 35°C; (3) 2-min seated WI at 12°C; (4) an ecologically relevant control consisting of 12 minutes walking at 5 km h−1. Muscle soreness, maximal voluntary contraction (MVC) of the knee flexors and extensors, hop distance, creatine kinase activity and myoglobin concentration were measured before exercise and in the 168 hours following the intervention. Between-group differences, time effects and interaction effects were investigated by mixed-model ANOVA. Results: The shuttle running exercise induced an increase in muscle soreness (1, 24, 48 and 72 hours post-intervention) creatine kinase activity and myoglobin concentration (post-exercise and 1, 24 and 48 hours post-intervention), and reduced MVC of the knee extensors (11% reduction at 24 hours, remaining reduced at 48 and 72 hours), flexors (24% reduction at 24 hours, remaining reduced at 24, 48, 72 and 168 hours), and hop distance (24 and 48 hours). However, no between-group differences or interaction effects were evident for any of these parameters. Conclusion: The WI protocols investigated were not better than light exercise in facilitating recovery from shuttle running exercise. Future studies examining the efficacy of WI as a recovery intervention should include a representative control condition to increase their relevance to sporting populations.

Physiology of cold water immersion: a comparison of cold water acclimatised and non-cold water acclimatised participants during static and dynamic immersions

Introduction Drowning is the third leading cause of accidental death worldwide. Many deaths from immersion in cold water are wrongly attributed to hypothermia. Humans can survive numerous hours in cold water, as seen in open water swimmers who complete endurance swims for many hours at low water temperatures. Previous studies performed on cold-water swimmers have shown distinct physiological differences in those regularly exposed to cold water compared to controls. The aim of this study was to identify whether regular cold water swimmers exhibit physiological adaptation to cold water immersion in static and dynamic conditions. Method A prospective case-control study, where participants were immersed in cold water (12°C); once during a static immersion and once during a swimming (dynamic) immersion. Six cold water acclimatised (CWAI) participants were matched to six non-cold water acclimatised participants for body fat percentage and gender for both the static and dynamic immersions and mean changed between the two groups compared. Results CWAI participants show a decreased metabolic rate leading to fall in core temperature during static immersion. In dynamic immersion, deep body temperature is maintained with little increase in metabolic heat production. Discussion CWAI participants show a hypothermic-type adaptation during static immersion in cold water. In contrast, an insulative-type adaptation is seen during dynamic immersion in the CWAI participants. The onset of shivering is delayed by adaptation to cold water. Insulative adaptation benefits the cold water swimmer as there is little or no increase in metabolic heat production. The swimmer can maintain their core temperature without wasting vital energy. Conclusion CWAI participants exhibit different types of adaptation depending on the type of immersion experienced.

Wearing a crotch strap on a correctly fitted lifejacket improves lifejacket performance

Wearing a lifejacket when immersed in water should support the wearer, maintaining their airway clear of the water. It is proposed that a retention system would improve airway protection by improving retention of the lifejacket around the torso. Study one (n = 10) quantified the performance of lifejackets immediately following a step into water from height when a lifejacket was worn with a crotch strap (two different tightness) and without a crotch strap. Airway freeboard was improved when wearing a crotch strap (P < 0.05) compared with no crotch strap. Study two used a manikin to examine the performance of lifejackets with and without a crotch strap during 3-h exposures to waves. During exposure to waves, the time taken to aspirate the lethal dose of seawater for drowning was doubled when wearing a crotch strap compared with the no-crotch-strap conditions (P < 0.001). Therefore, wearing a crotch strap (functioning retention system) on a correctly fitted lifejacket improves airway protection following accidental immersion and prolonged wave exposure. Practitioner Summary: Following a step from height into water, wearing a crotch strap on a correctly fitted lifejacket improved lifejacket performance. Wearing a lifejacket with the crotch strap fitted minimised the reduction in lifejacket performance, compared with the no-crotch-strap condition, when exposed to waves for 3 h.

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 Friedmans 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.

Validation of One-Mile Walk Equations for the Estimation of Aerobic Fitness in British Military Personnel Under the Age of 40 Years

OBJECTIVE To provide an accurate estimate of peak oxygen uptake (VO2 peak) for British Royal Navy Personnel aged between 18 and 39, comparing a gold standard treadmill based maximal exercise test with a submaximal one-mile walk test. METHODS Two hundred military personnel consented to perform a treadmill-based VO2 peak test and two one-mile walk tests round an athletics track. The estimated VO2 peak values from three different one-mile walk equations were compared to directly measured VO2 peak values from the treadmill-based test. One hundred participants formed a validation group from which a new equation was derived and the other 100 participants formed the cross-validation group. RESULTS Existing equations underestimated the VO2 peak values of the fittest personnel and overestimated the VO2 peak of the least aerobically fit by between 2% and 18%. The new equation derived from the validation group has less bias, the highest correlation with the measured values (r = 0.83), and classified the most people correctly according to the Royal Navys Fitness Test standards, producing the fewest false positives and false negatives combined (9%). CONCLUSION The new equation will provide a more accurate estimate of VO2 peak for a British military population aged 18 to 39.

A report on the Global Open Water Swimming (GOWS) Conference, Cork, Ireland, 12th October 2013

The third Global Open Water Swimming Conference was for the first time held in Europe. Researchers, swim pioneers and leading marathon swimmers came together to present research related to the water environment, pioneer swims, young and old marathon swimmers and human physiology.