Habituation of the cold shock response: A systematic review and meta-analysis

Cold water immersion (CWI) evokes the life-threatening reflex cold shock response (CSR), inducing hyperventilation, increasing cardiac arrhythmias, and increasing drowning risk by impairing safety behaviour. Repeated CWI induces CSR habituation (i.e., diminishing response with same stimulus magnitude) after ∼4 immersions, with variation between studies. We quantified the magnitude and coefficient of variation (CoV) in the CSR in a systematic review and meta-analysis with search terms entered to Medline, SportDiscus, PsychINFO, Pubmed, and Cochrane Central Register. Random effects meta-analyses, including effect sizes (Cohen's d) from 17 eligible groups (k), were conducted for heart rate (HR, n = 145, k = 17), respiratory frequency (fR, n = 73, k = 12), minute ventilation (Ve, n = 106, k = 10) and tidal volume (Vt, n = 46, k=6). All CSR variables habituated (p < 0.001) with large or moderate pooled effect sizes: ΔHR -14 (10) bt. min-1 (d: -1.19); ΔfR -8 (7) br. min-1 (d: -0.78); ΔVe, -21.3 (9.8) L. min-1 (d: -1.64); ΔVt -0.4 (0.3) L -1. Variation was greatest in Ve (control vs comparator immersion: 32.5&24.7%) compared to Vt (11.8&12.1%). Repeated CWI induces CSR habituation potentially reducing drowning risk. We consider the neurophysiological and behavioural consequences.

No effect of prefrontal transcranial direct current stimulation (tDCS) on food craving, food reward and subjective appetite in females displaying mild-to-moderate binge-type behaviour

Previous work suggests there may be an effect of transcranial direct current stimulation (tDCS) on appetite control in people at risk of overconsumption, however findings are inconsistent. This study aimed to further understand the potential eating behaviour trait-dependent effect of tDCS, specifically in those with binge-type behaviour. Seventeen females (23 ± 7 years, 25.4 ± 3.8 kg m-2) with mild-to-moderate binge eating behaviour completed two sessions of double-blind, randomised and counterbalanced anodal and sham tDCS applied over the right dorsolateral prefrontal cortex at 2.0 mA for 20 min. Subjective appetite visual analogue scales (VAS), the Food Craving Questionnaire-State (FCQ-S), and Leeds Food Preference Questionnaire (LFPQ) were completed pre- and post-tDCS. Participants then consumed a fixed-energy meal, followed by the VAS, FCQ-S and LFPQ. No difference between pre- and post-tDCS scores were found across fullness (p = 0.275, BF10 = 0.040), prospective consumption (p = 0.127, BF10 = 0.063), desire to eat (p = 0.247, BF10 = 0.054) or FCQ-S measures (p = 0.918, BF10 = 0.040) when comparing active and sham protocols. Only explicit liking and wanting for high-fat sweet foods were significantly different between conditions, with increased scores following active tDCS. When controlling for baseline hunger, the significant differences were removed (p = 0.138 to 0.161, BF10 = 0.810 to 1.074). The present data does not support the eating behaviour trait dependency of tDCS in a specific cohort of female participants with mild-to-moderate binge eating scores, and results align with those from individuals with healthy trait scores. This suggests participants with sub-clinical binge eating behaviour do not respond to tDCS. Future work should further explore effects in clinical and sub-clinical populations displaying susceptibility to overconsumption and weight gain.

Influence of acute beetroot juice supplementation on cold-induced vasodilation and fingertip rewarming

PURPOSE

Vasoactive ingredients in beetroot (BR) such as nitrate are known to induce vasodilation in temperate conditions. This study investigated the effect of BR ingestion on cold induced vasodilation (CIVD) and rewarming of finger skin temperature (T_fing) during and after hand immersion in cold water.

METHODS

Twenty healthy males (mean ± SD; age 22.2 ± 0.7 years, height 172.6 ± 6.0 cm, body mass 61.3 ± 11.7 kg) repeated a hand cold water immersion test twice with prior BR or water beverage ingestion (randomised order). They rested for 2 h in thermoneutral conditions (27 °C, 40% relative humidity) after consuming the beverage, then immersed their non-dominant hand in 8 °C water for 30 min. They then rewarmed their hand in the ambient air for 20 min. Skin temperature at seven body sites, T_fing, finger skin blood flow (SkBF_fing), and blood pressure were measured.

RESULTS

During hand immersion parameters of CIVD (T_fing and SkBF_fing) were not different between BR and water conditions although skin temperature gradient from proximal to distal body sites was significantly smaller with BR (P < 0.05). During rewarming, SkBF_fing and cutaneous vascular conductance were significantly higher with BR than with water (P < 0.05). The rewarming speed in T_fing and SkBF_fing was significantly faster with BR at 15- (BR 1.24 ± 0.22 vs water 1.11 ± 0.26 °C/min) and 20-min rewarming (P < 0.05). Additionally, individuals with slower rewarming speed with water demonstrated accelerated rewarming with BR supplementation.

CONCLUSION

BR accelerated rewarming in T_fing and SkBF_fing after local cold stimulus, whereas, CIVD response during hand cold immersion was not affected by BR ingestion.

Quantifying the Peak Physical Match-Play Demands of Professional Soccer Substitutes Following Pitch-Entry: Assessing Contextual Influences

Purpose: To quantify the peak post-pitch-entry physical responses of soccer substitutes while assessing contextual influences. Peak responses may be important performance indicators for substitutes introduced to provide a physical impact. Method: Thirty-three professional substitutes wore Microelectromechanical Systems during 44 matches (4 ± 3 observations·player^-1). Post-pitch-entry relative peak values for total and high-speed (> 5.5 m·s^-1) distances, average acceleration, and PlayerLoad™ were calculated using rolling averages over 60-s to 600-s. Linear mixed models assessed contextual influences (position, substitution timing, scoreline, and location). Results: Substitutes introduced during the final ~15 min of match-play covered less high-speed distance than first-half substitutes (~2.8-3.1 m·min^-1) over 480-s to 600-s epochs, and less than 60:00-74:59 min substitutes (~1.7-1.8 m·min^-1) during 540-s and 600-s epochs. Average acceleration during all except 180-s epochs was lower for 75:00+ min substitutes compared with first-half replacements (~0.27-0.43 m·s^-2), and lower than 60:00-74:59 min substitutes during 60-s (~0.13 m·s^-2). Substitutes introduced when their team was winning recorded greater distances over 120-s to 600-s (~6.2-7.7 m·min^-1), and higher PlayerLoad™ values during 120-s, 180-s, 300-s, and 480-s epochs (~2.7-3.6 arbitrary units·min^-1), compared with when scores were level at pitch-entry. Irrespective of substitution timing, substitute midfielders exceeded the total distance of substitute attackers (~5.9-16.2 m·min^-1) for all except 360-s and 600-s epochs, and defenders (~13.3-26.7 m·min^-1) during epochs < 300-s. Conclusions: This study provides benchmark data for practitioners tailoring training and recovery protocols, particularly "top-up" conditioning, to the competitive demands of soccer substitutes. Knowing how contextual factors influence substitutes' peak match-play responses may help managers/coaches assess the efficacy of substitution strategies.

Modulating eating behavior with transcranial direct current stimulation (tDCS): A systematic literature review on the impact of eating behavior traits

Transcranial direct current stimulation (tDCS) is becoming an increasingly popular technique for altering eating behaviors. Recent research suggests a possible eating behavior trait-dependent effect of tDCS. However, studies recruit participant populations with heterogeneous trait characteristics, including "healthy" individuals who do not present with eating behavior traits suggesting susceptibility to overconsumption. The present review considers the effects of tDCS across eating-related measures and explores whether a trait-dependent effect is evident across the literature. A literature search identified 28 articles using sham-controlled tDCS to modify eating-related measures. Random effects meta-analyses were performed, with subgroup analyses to identify differences between "healthy" and trait groups. Trivial overall effects (g = -0.12 to 0.09) of active versus sham tDCS were found. Subgroup analyses showed a more consistent effect for trait groups, with small and moderate effect size (g = -1.03 to 0.60), suggesting tDCS is dependent on participants' eating behavior traits. Larger effect sizes were found for those displaying traits associated with study outcomes (e.g., heightened food cravings). "Healthy" individuals appear to be unresponsive to stimulation. Based on this meta data, future work should recruit those with eating behavior trait susceptibilities to overconsumption, focusing on those who present with traits associated with the outcome of interest.

The water incident database (WAID) 2012 to 2019: a systematic evaluation of the documenting of UK drownings

Background

Death by drowning is a leading cause of accidental death in the United Kingdom (UK) and worldwide. The World Health Organization (WHO) states that effective documentation of drowning is required to describe drowning frequency and to underpin effective drowning prevention intervention, thus improving the quality of data describing drowning frequency represents a key initiative. The water incident database (WAID) has been used to document UK fatal and non-fatal water-based incidents since 2009. WAID has not undergone a systematic evaluation of its data or data collection procedures to establish if the database meets the WHO requirements. The present study investigated the characteristics of UK fatal drowning incidents and audited current WAID data capture procedures.

Methods

Data for the fatal drowning cases recorded between 2012 and 2019 were reviewed. Descriptive data were generated 1) to describe fatal drownings in the UK’s WAID in this period; 2) a sub-set of drownings were audited i) for completeness of data entry and, based on source documents, ii) for quality of data entry; 3) these processes were used to make recommendations for onward revisions to WAID.

Results

A total of 5051 fatalities were recorded between 2012 and 2019. Drowning was most frequent amongst males aged 35 to 60 years (n = 1346), whilst suspected accidents and suicides accounted for 44 and 35% of fatalities. Suicide by drowning was at a peak in the most recent year of data analysed (i.e., 2019; 279 cases) highlighting an urgent need for targeted intervention. Audit part 2i) indicated that 16% of all fields were incomplete, thus indicating potential redundancy, duplication, or the need for onward review. Audit part 2ii) indicated high levels of agreement (80 ± 12%) between audited cases and the ‘true’ WAID entries.

Conclusions

This study confirms WAID as a rigorous, transparent and effective means of documenting UK drownings thereby meeting WHO requirements for data quality; yet future improvements are recommended. Such findings allow researchers and policy makers to use WAID to further investigate UK drowning with a view to improving public safety measures and drowning prevention interventions. Observations alongside several expert recommendations have informed a revised version of WAID.

Promoting physical activity through text messages: the impact of attitude and goal priority messages

Introduction

Many young adults demonstrate insufficient rates of physical activity (PA) to yield health benefits. The study tested the effectiveness of a text messaging intervention targeting key psychological determinants and PA.

Methods

Participants received either attitude messages, goal priority messages, a combination of these, or generic PA information (control). After confirming that groups were matched at baseline, a 2 (attitude: yes vs. no) by 2 (goal priority: yes vs. no) by 2 (time: immediately post-intervention, four weeks post-intervention) randomized control trial tested main and interactive effects.

Results

Results showed participants that received attitude messages had significantly more positive attitudes, intentions and rates of PA. Mediational analyses showed the influence of attitude messages on PA to be fully mediated through the serial path via attitude and intention. There were no other main or interactive effects.

Conclusion

The study provides support for using attitudinal messages delivered via text messaging to influence key psychological determinants and PA.

Body temperature and physical performance responses are not maintained at the time of pitch-entry when typical substitute-specific match-day practices are adopted before simulated soccer match-play

OBJECTIVES

To profile performance and physiological responses to typical patterns of match-day activity for second-half soccer substitutes.

DESIGN

Descriptive.

METHODS

Following a warm-up, 13 male team sports players underwent ∼85min of rest, punctuated with five min rewarm-ups at ∼25, ∼50, and ∼70min, before ∼30min of simulated soccer match-play. Countermovement jump performance (jump height, peak power output), alongside 15m sprints, were assessed post-warm-up, and pre- and post-simulated match-play. Core temperature, heart rate, ratings of perceived exertion, and blood glucose and lactate concentrations were measured throughout.

RESULTS

Warm-up-induced core temperature elevations (∼2.3%, +0.85°C; p<0.001) were maintained until after the first rewarm-up. Thereafter, core temperature was reduced from post-warm-up values until pre-simulated match-play (∼1.6%, -0.60°C; p<0.001), where values were similar to pre-warm-up (37.07±0.24°C, p=0.981). Simulated match-play increased core temperature progressively (p≤0.05) but values remained lower than post-warm-up (∼5min; p=0.002) until ∼10min into exercise. From post-warm-up to pre-simulated match-play, sprint times (∼3.9%, +0.10s, p=0.003), jump height (∼9.4%, -3.1cm; p=0.017), and peak power output (∼7.2%, -296W; p<0.001) worsened. Despite increased ratings of perceived exertion and elevated blood lactate concentrations (p≤0.05), sprint times were maintained throughout exercise, whereas peak power increased (∼7.8%, +294W; p=0.006) pre- to post-exercise.

CONCLUSIONS

At the point of simulated pitch-entry, body temperature and physical performance responses were not maintained from warm-up cessation despite typical substitute-specific match-day practices being employed in thermoneutral conditions. Evidence of performance-limiting fatigue was absent during ∼30min of simulated match-play. These data question the efficacy of practices typically implemented by substitutes before pitch-entry.

The effect of transcranial direct current stimulation (tDCS) on food craving, reward and appetite in a healthy population

The ability to control hedonic appetite is associated with executive functioning, originating in the prefrontal cortex (PFC). These rewarding components of food can override homeostatic mechanisms, potentiating obesogenic behaviours. Indeed, those susceptible to overconsumption appear to have PFC hypo-activation. Transcranial direct current stimulation (tDCS) over the dorsolateral PFC (DLPFC) has been shown to reduce food craving and consumption, potentially via attenuating this reward response. We examined the effects of stimulation on food reward and craving using a healthy-weight cohort. This study is amongst the first to explore the effects of tDCS on explicit and implicit components of reward for different food categories. Twenty-one healthy-weight participants (24 ± 7 years, 22.8 ± 2.3 kg m^-2) completed two sessions involving double-blind, randomised and counterbalanced anodal or sham tDCS over the right DLPFC, at 2 mA for 20 min. Food craving (Food Craving Questionnaire-State), reward (Leeds Food Preference Questionnaire), and subjective appetite (100 mm visual analogue scales) were measured pre- and post-tDCS. Eating behaviour trait susceptibility was assessed using the Three Factor Eating Questionnaire-Short Form, Control of Eating Questionnaire, and Food Craving Questionnaire-Trait-reduced. Stimulation did not alter food craving, reward or appetite in healthy-weight participants who displayed low susceptibility to overconsumption, with low trait craving, good craving control, and low uncontrolled eating and emotional eating behaviour. Implicit and explicit reward were reliable measures of hedonic appetite, suggesting these are robust targets for future tDCS research. These findings suggest that applying tDCS over the DLPFC does not change food reward response in individuals not at risk for overconsumption, and future work should focus on those at risk of overconsumption who may be more responsive to the effects of tDCS on hedonic appetite.

Menthol as an Ergogenic Aid for the Tokyo 2021 Olympic Games: An Expert-Led Consensus Statement Using the Modified Delphi Method

INTRODUCTION

Menthol topical application and mouth rinsing are ergogenic in hot environments, improving performance and perception, with differing effects on body temperature regulation. Consequently, athletes and federations are beginning to explore the possible benefits to elite sport performance for the Tokyo 2021 Olympics, which will take place in hot (~ 31 °C), humid (70% RH) conditions. There is no clear consensus on safe and effective menthol use for athletes, practitioners, or researchers. The present study addressed this shortfall by producing expert-led consensus recommendations.

METHOD

Fourteen contributors were recruited following ethical approval. A three-step modified Delphi method was used for voting on 96 statements generated following literature consultation; 192 statements total (96/96 topical application/mouth rinsing). Round 1 contributors voted to "agree" or "disagree" with statements; 80% agreement was required to accept statements. In round 2, contributors voted to "support" or "change" their round 1 unaccepted statements, with knowledge of the extant voting from round 1. Round 3 contributors met to discuss voting against key remaining statements.

RESULTS

Forty-seven statements reached consensus in round 1 (30/17 topical application/rinsing); 14 proved redundant. Six statements reached consensus in round 2 (2/4 topical application/rinsing); 116 statements proved redundant. Nine further statements were agreed in round 3 (6/3 topical application/rinsing) with caveats.

DISCUSSION

Consensus was reached on 62 statements in total (38/24 topical application/rinsing), enabling the development of guidance on safe menthol administration, with a view to enhancing performance and perception in the heat without impairing body temperature regulation.

Profiling the Post-match Top-up Conditioning Practices of Professional Soccer Substitutes: An Analysis of Contextual Influences

Hills, SP, Barrett, S, Busby, M, Kilduff, LP, Barwood, MJ, Radcliffe, JN, Cooke, CB, and Russell, M. Profiling the post-match top-up conditioning practices of professional soccer substitutes: An analysis of contextual influences. J Strength Cond Res 34(10): 2805-2814, 2020-Soccer practitioners implement "top-up" conditioning sessions to compensate for substitutes' limited match-play exposure. Although perceived to be valuable for reducing injury risk and augmenting positive physical adaptations, little research has considered the demands of post-match top-up training. To quantify post-match top-up responses, 31 professional soccer players wore 10 Hz microelectromechanical systems after 37 matches whereby they were selected in the match-day squad as substitutes (184 observations; 6 ± 5 observations·player). Linear mixed models and effect sizes (ES) assessed the influence of contextual factors on 23 physical performance variables. Top-ups lasted 17.13 ± 7.44 minutes, eliciting total and high-speed distances of 1.7 ± 6.2 km and 0.4 ± 1.7 km, respectively. Each contextual factor (i.e., position, substitution timing, match location, result, time of day, stage of the season, and fixture density) influenced at least 4 of the dependent variables profiled (p ≤ 0.05). Top-up duration; total, moderate-speed, and low-speed distance; and the number of repeated high-intensity efforts were greater for unused vs. used substitutes (ES: 0.38-0.73, small to moderate). Relative to away matches, home top-ups elicited heightened total, low-speed, and high-speed distances, alongside more moderate-speed accelerations and decelerations, and repeated high-intensity efforts (ES: 0.25-0.89, small to moderate). Although absolute and relative running distances were generally the highest when the fixture density was low, the greatest acceleration and deceleration demands were observed during the most congested fixture periods. Late-season top-ups typically elicited lower absolute physical responses than early and mid-season sessions. These data provide important information for practitioners when considering the aims and design of substitute top-up conditioning sessions, particularly with reference to contextual influences.

Testing traditions in cycling: newspapers are effective thermal insulators during simulated downhill cycling

BACKGROUND

Cycling downhill accelerates heat loss and requires lower work rates leading to cold discomfort. Historically, cyclists have behaviorally thermoregulated prior to cycling downhill by inserting newspapers into their jerseys. Yet, there is no experimental data to support such a method showing improvements in thermal perception and profile; we hypothesized it would.

METHODS

Two cohorts (N.=8 each) of male participants completed two main trials each involving 30-minutes simulated uphill cycling (65% VO<inf>2peak</inf> 188 [41] W; no fan) followed by 15-minutes downhill cycling (35% VO<inf>2peak</inf> 41 [12] W) in front of an industrial fan (wind speed: 4.6 [0.1] m·s^-1). In one trial participants inserted one (study 1) or two (study 2) tabloid newspapers into their jerseys (PAPER) prior to downhill cycling; the other was a control (NOPAPER). Whole body and torso thermal sensation (TS) and comfort (TC), aural temperature (T<inf>au</inf>), skin temperature (T<inf>skin</inf>), and newspaper mass change (∆) were measured. Data were compared using ANOVA and t-test to 0.05 alpha level.

RESULTS

After uphill cycling thermal and perceptual profiles were similar. In study 1, only TC was transiently improved 1-minute after newspaper insertion. In study 2, T<inf>skin</inf> rate of decline was lower in the PAPER condition (-0.11 [0.12] °C.min^-1 cf -0.53 [0.16] °C.min^-1; P=0.001) and T<inf>chest</inf> remained higher (28.83 [3.17] °C cf 24.39 [3.22] °C). This improved TS but not TC. Newspaper mass increased indicating impaired sweat evaporation (∆<inf>mass</inf>: 5.7 [4.9] g; P=0.01).

CONCLUSIONS

Thermal perception and profile during downhill cycling was improved by inserting two newspapers but not one newspaper into the jersey, supporting our hypothesis.

Profiling the Responses of Soccer Substitutes: A Review of Current Literature

Depending upon competition regulations, the laws of soccer allow between three and an unlimited number of substitutions that can be made on either a permanent or rolling basis. Substitutes are typically introduced to minimise/offset the effects of fatigue, alter tactics, replace players deemed as underperforming or injured, and/or give playing time to youth players or to squad members returning from injury. While the match-day practices of substitutes include participation in the pre-match warm-up, and sporadic periods of rewarm-up activity, it is currently unclear as to whether these pre-entry preparations facilitate optimal match performance thereafter. Acknowledging the contextual factors that possibly influence substitutes' performance, this review summarises the presently available literature on soccer substitutes, and makes recommendations for future research. Literature searching and screening yielded 13 studies, which have typically focused on characterising: (1) the patterns, including timing, of substitutes' introduction; (2) indices of match-performance; and (3) the emotional experiences of soccer substitutes. The majority of substitutions occur after the first-half has ended (i.e. at half-time or during the second-half), with introduced players exceeding the second-half physical performances of those who started the match. Observations of progressive improvements in running performance as playing time increases, and findings that substitutes mostly experience negative emotions, highlight the potential inadequacies of pre-match preparations, and present future research opportunities. Additional work is therefore needed to confirm these findings and to determine the efficacy of current preparation strategies, thereby providing opportunities to assess then address substitutes' pre-pitch entry preparations, on-field performance and emotional responses.

A match-day analysis of the movement profiles of substitutes from a professional soccer club before and after pitch-entry

Whilst the movement demands of players completing a whole soccer match have been well-documented, comparable information relating to substitutes is sparse. Therefore, this study profiled the match-day physical activities performed by soccer substitutes, focusing separately on the pre and post pitch-entry periods. Seventeen English Championship soccer players were monitored using 10 Hz Micromechanical Electrical Systems (MEMS) devices during 13 matches in which they participated as substitutes (35 observations). Twenty physical variables were examined and data were organised by bouts of warm-up activity (pre pitch-entry), and five min epochs of match-play (post pitch-entry). Linear mixed modelling assessed the influence of time (i.e., ‘bout’ and ‘epoch’), playing position, and match scoreline. Substitutes performed 3±1 rewarm-up bouts∙player^-1∙match^-1. Compared to the initial warm-up, each rewarm-up was shorter (-19.7 to -22.9 min) and elicited less distance (-606 to -741 m), whilst relative total distances were higher (+26 to +69 m∙min^-1). Relative total (+13.4 m∙min^-1) and high-speed (+0.4 m∙min^-1) distances covered during rewarm-ups increased (p <0.001) with proximity to pitch-entry. Players covered more (+3.2 m; p = 0.047) high-speed distance per rewarm-up when the assessed team was losing compared with when winning at the time of pitch-entry. For 10 out of 20 variables measured after pitch-entry, values reduced from 0–5 min thereafter, and substitutes covered greater (p ˂0.05) total (+67 to +93 m) and high-speed (+14 to +33 m) distances during the first five min of match-play versus all subsequent epochs. Midfielders covered more distance (+41 m) per five min epoch than both attackers (p ˂0.001) and defenders (p = 0.016). Acknowledging the limitations of a solely movement data approach and the potential influence of other match-specific factors, such findings provide novel insights into the match-day demands faced by substitute soccer players. Future research opportunities exist to better understand the match-day practices of this population.

The Effect of Head-to-Head Competition on Behavioural Thermoregulation, Thermophysiological Strain and Performance During Exercise in the Heat

Background

It has been suggested that pacing is a thermoregulatory behaviour. We investigated the effect of competition on pacing, performance and thermophysiological strain during exercise in the heat and the psychological factors mediating competition effects.

Method

Eighteen males (maximum oxygen uptake [VO_2max] 3.69 [0.44] L min⁻¹) undertook a preliminary 20-km cool (wet-bulb globe temperature [WBGT] 12 °C) cycling time trial (TT) and three experimental 20-km trials (balanced order): (i) cool TT (CoolSolo); (ii) hot (WBGT 26 °C) TT (HotSolo); (iii) hot head-to-head competition (HotH2H). During TTs, an avatar of the participant’s performance was visible. During HotH2H, participants believed they were competing against another participant, but the competitor’s avatar replicated their own preliminary (cool) TT.

Results

TTs (min:sec [SD]) slowed with increased ambient temperature [CoolSolo 35:31 (2:11) versus HotSolo 36:10 (2:26); p = 0.011]. This effect was negated by competition; performances were not different between HotH2H [35:17 (1:52)] and CoolSolo (p = 0.160) and were quicker in HotH2H versus HotSolo (p = 0.001). End-exercise rectal temperature, mean body temperature and physiological strain index were (p < 0.05) higher in HotH2H than either solo condition. Despite faster performance and greater thermophysiological strain, rating of perceived exertion (RPE), thermal comfort and sensation, and perceptual strain index were not different between HotH2H and HotSolo. The difference in end-exercise rectal temperature between HotH2H and HotSolo was related to pre-exercise anticipatory heart rate response (r = 0.608, p = 0.010) and participants’ propensity for deliberate risk-taking (B = 0.12, p < 0.001), whereas self-reported resilience predicted change in performance times between HotH2H versus HotSolo (B = − 9.40, p = 0.010).

Conclusion

Competition changes the relationship between perceived and actual thermophysiological state, altering behavioural thermoregulation and increasing thermophysiological strain; this could increase heat-illness risk. Psychophysiological and psychological measures may identify susceptible individuals.

The effect of hot and cold drinks on thermoregulation, perception, and performance: the role of the gut in thermoreception

PURPOSE

Hot compared to cold drinks alter sweating responses during very low intensity exercise in temperate conditions. The thermoregulatory, perceptual, and performance effects of hot compared to cold drinks in hot, dry conditions during high-intensity exercise have not been examined.

METHOD

Ten participants [mean ± SD characteristics age 25 ± 5 years, height 1.81 ± 0.07 m, body mass 73.5 ± 10.6 kg, maximal power output (P_Max) 350 ± 41 W] completed two conditions, where they drank four boluses (ingested at - 9, 15, 30, and 45 min, respectively) of 3.2 mL kg^- 1 (~ 960 mL total) of either a COLD (5.3 °C) or a HOT drink (49.0 °C), which were contrasted to a no-drink CONTROL. They cycled for 60-min [55% P_Max in hot (34.4 °C) dry (34% RH)] ambient conditions followed by a test to exhaustion (TTE; 80% P_Max). The thermoregulatory, performance, and perceptual implications of drink temperature were measured.

RESULTS

TTE was worse in the CONTROL (170 ± 132 s) than the COLD drink (371 ± 272 s; p = 0.021) and HOT drink conditions (367 ± 301 s; p = 0.038) which were not different (p = 0.965). Sweat responses [i.e., reflex changes in mean skin temperature (T_msk) and galvanic skin conductance] indicated transient reductions in sweating response after COLD drink ingestion. The COLD drink improved thermal comfort beyond the transient changes in sweating.

CONCLUSION

Only COLD drink ingestion changed thermoregulation, but improved perceptual response. Accordingly, we conclude a role for gut thermoreception in thermal perception during exercise in hot, dry conditions.

Acute Anxiety Predicts Components of the Cold Shock Response on Cold Water Immersion: Toward an Integrated Psychophysiological Model of Acute Cold Water Survival

Introduction: Drowning is a leading cause of accidental death. In cold-water, sudden skin cooling triggers the life-threatening cold shock response (CSR). The CSR comprises tachycardia, peripheral vasoconstriction, hypertension, inspiratory gasp, and hyperventilation with the hyperventilatory component inducing hypocapnia and increasing risk of aspirating water to the lungs. Some CSR components can be reduced by habituation (i.e., reduced response to stimulus of same magnitude) induced by 3–5 short cold-water immersions (CWI). However, high levels of acute anxiety, a plausible emotion on CWI: magnifies the CSR in unhabituated participants, reverses habituated components of the CSR and prevents/delays habituation when high levels of anxiety are experienced concurrent to immersions suggesting anxiety is integral to the CSR.

Purpose: To examine the predictive relationship that prior ratings of acute anxiety have with the CSR. Secondly, to examine whether anxiety ratings correlated with components of the CSR during immersion before and after induction of habituation.

Methods: Forty-eight unhabituated participants completed one (CON1) 7-min immersion in to cold water (15°C). Of that cohort, twenty-five completed four further CWIs that would ordinarily induce CSR habituation. They then completed two counter-balanced immersions where anxiety levels were increased (CWI-ANX) or were not manipulated (CON2). Acute anxiety and the cardiorespiratory responses (cardiac frequency [f_c], respiratory frequency [f_R], tidal volume [V_T], minute ventilation [_E]) were measured. Multiple regression was used to identify components of the CSR from the most life-threatening period of immersion (1^st minute) predicted by the anxiety rating prior to immersion. Relationships between anxiety rating and CSR components during immersion were assessed by correlation.

Results: Anxiety rating predicted the f_c component of the CSR in unhabituated participants (CON1; p < 0.05, r = 0.536, r²= 0.190). After habituation immersions (i.e., cohort 2), anxiety rating predicted the f_R component of the CSR when anxiety levels were lowered (CON2; p < 0.05, r = 0.566, r²= 0.320) but predicted the f_c component of the CSR (p < 0.05, r = 0.518, r²= 0.197) when anxiety was increased suggesting different drivers of the CSR when anxiety levels were manipulated; correlation data supported these relationships.

Discussion: Acute anxiety is integral to the CSR before and after habituation. We offer a new integrated model including neuroanatomical, perceptual and attentional components of the CSR to explain these data.

Changes in lung function during exercise are independently mediated by increases in deep body temperature

Background

This study examined whether an increase in deep body temperature contributes to increases in ventilatory flow indicative of bronchodilatation.

Method

The study employed a within-participant repeated measures design. Nine participants (mean (SD): age 22 (3) years; height 177.7 (8.3) cm; mass 80.2 (19.1) kg) completed three conditions: exercise (EXERC; 30 min); 40°C water immersion (IMM40; 30 min) to passively raise rectal temperature (T_re) and 35°C immersion (IMM35; 30 min) asa thermoneutral control for IMM40. A forced vital capacity (FVC) manoeuvre was performed at the start of the test and every 10 min thereafter. Forced expiratory volume in 1 s (FEV₁), FEV₁/FVC, 25%, 50% and 75% maximal expiratory flow during FVC (forced expiratory flow (FEF)25, FEF50, FEF75) were also measured. Data were compared using a repeated measures two-way analysis of variance, with a 0.05 α level.

Results

Rectal temperature (T_re) peaked after 30 min in the EXERC (mean (SD) 38.0 (0.3)°C) and IMM40 (38.2 (0.2)°C) conditions and both were higher (p<0.05) than at the corresponding time in the thermoneutral condition (37.2 (0.2)°C). At this time, FEV₁ was 4.5 (0.6), 4.6 (0.3) and 4.4 (0.6) L, respectively. T_re, FEV₁ and FEV₁/FVC were greater in the IMM40 and EXERC conditions compared with the IMM35 condition. Interaction effects were evident for FEF50 and FEF75 (p<0.05), being higher in IMM40 and EXERC conditions.

Conclusion

Increasing deep body temperature, independently, contributes to the increased airflow ascribed to bronchodilatation when exercising.

North Pole Marathon Laboratory Lessons and Field Success

BACKGROUND

This case study documents the training, laboratory preparation, and in-race performance data from Great Britain's top finisher in the 13(th) edition of the UVU North Pole Marathon.

CASE REPORT

We report data from a preparatory laboratory test in simulated cold conditions (-15°C) with and without wind chill during high- and low-intensity expected 'race pace' running. These tests examined the adequacy of the selected clothing assembly and provided recommendations for the race. The tests established that there was no risk of hypothermia, as the clothing assembly provided too much insulation; terminal rectal temperature was 39.25°C. Skin temperature (Tsk) data revealed no impending risk of frostbite; nadir Tsk was 20.2°C at the hamstring. Oxygen consumption data revealed the self-selected high intensity was potentially not sustainable based on estimates of substrate utilization. We recommended: 1) a maximum running speed; 2) some of the clothing base layers could be removed pre-race; 3) vents and/or zips could be used to offload or retain heat; and 4) an even pacing profile should be adopted.

DISCUSSION

The participant completed the race in 6:55:24 (h:mm:ss) in temperatures of -41°C. GPS data revealed a positive pacing template (i.e., marginally quicker in the first half). Neither hypothermia nor frostbite occurred. Peak pace from the laboratory tests was not consistently exceeded. Marathon performance can be undertaken in one of the world's most inhospitable environments when careful consideration is given to clothing insulation and exercise intensity by planning for the dynamic thermal changes that may occur as the race ensues.

The influence of a menthol and ethanol soaked garment on human temperature regulation and perception during exercise and rest in warm, humid conditions

This study assessed whether donning a garment saturated with menthol and ethanol (M/E) can improve evaporative cooling and thermal perceptions versus water (W) or nothing (CON) during low intensity exercise and rest in warm, humid conditions often encountered in recreational/occupational settings. It was hypothesised there would be no difference in rectal (Tre) and skin (Tsk) temperature, infra-red thermal imagery of the chest/back, thermal comfort (TC) and rating of perceived exertion (RPE) between M/E, W and CON, but participants would feel cooler in M/E versus W or CON.

METHODS

Six volunteers (mean [SD] 22 [4] years, 72.4 [7.4] kg and 173.6 [3.7] cm) completed (separate days) three, 60-min tests in 30°C, 70%rh, in a balanced order. After 15-min of seated rest participants donned a dry (CON) or 80mL soaked (M/E, W) long sleeve shirt appropriate to their intervention. They then undertook 30-min of low intensity stepping at a rate of 12steps/min on a 22.5cm box, followed by 15-min of seated rest. Measurements included heart rate (HR), Tre, Tsk (chest/back/forearm), thermal imaging (back/chest), thermal sensation (TS), TC and RPE. Data were reported every fifth minute as they changed from baseline and the area under the curves were compared by condition using one-way repeated measures ANOVA, with an alpha level of 0.05.

RESULTS

Tre differed by condition, with the largest heat storage response observed in M/E (p<0.05). Skin temperature at the chest/back/forearm, and thermal imaging of the chest all differed by condition, with the greatest rate of heat loss observed in W and M/E respectively (p<0.01). Thermal sensation differed by condition, with the coolest sensations observed in M/E (p<0.001). No other differences were observed.

CONCLUSIONS

Both M/E and W enhanced evaporative cooling compared CON, but M/E causes cooler sensations and a heat storage response, both of which are likely mediated by menthol.

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.

Relieving thermal discomfort: Effects of sprayed L-menthol on perception, performance, and time trial cycling in the heat

L-menthol stimulates cutaneous thermoreceptors and induces cool sensations improving thermal comfort, but has been linked to heat storage responses; this could increase risk of heat illness during self-paced exercise in the heat. Therefore, L-menthol application could lead to a discrepancy between behavioral and autonomic thermoregulatory drivers. Eight male participants volunteered. They were familiarized and then completed two trials in hot conditions (33.5 °C, 33% relative humidity) where their t-shirt was sprayed with CONTROL-SPRAY or MENTHOL-SPRAY after 10 km (i.e., when they were hot and uncomfortable) of a 16.1-km cycling time trial (TT). Thermal perception [thermal sensation (TS) and comfort (TC)], thermal responses [rectal temperature (Trec ), skin temperature (Tskin )], perceived exertion (RPE), heart rate, pacing (power output), and TT completion time were measured. MENTHOL-SPRAY made participants feel cooler and more comfortable and resulted in lower RPE (i.e., less exertion) yet performance was unchanged [TT completion: CONTROL-SPRAY 32.4 (2.9) and MENTHOL-SPRAY 32.7 (3.0) min]. Trec rate of increase was 1.40 (0.60) and 1.45 (0.40) °C/h after CONTROL-SPRAY and MENTHOL-SPRAY application, which were not different. Spraying L-menthol toward the end of self-paced exercise in the heat improved perception, but did not alter performance and did not increase heat illness risk.

Barefoot running improves economy at high intensities and peak treadmill velocity

AIM

Barefoot running can improve running economy (RE) compared to shod running at low exercise intensities, but data is lacking for the higher intensities typical during many distance running competitions. The influence of barefoot running on the velocity at maximal oxygen uptake (vVO2max) and peak incremental treadmill test velocity (vmax) is unknown. The present study tested the hypotheses that barefoot running would improve RE, vVO2max and vmax relative to shod running.

METHODS

Using a balanced within-subject repeated measures design, eight male runners (aged 23.1±4.5 years, height 1.80±0.06 m, mass 73.8±11.5 kg, VO2max 4.08±0.39 L·min(-1)) completed a familiarization followed by one barefoot and one shod treadmill running trial, 2-14 days apart. Trial sessions consisted of a 5 minute warm-up, 5 minute rest, followed by 4×4 minute stages, at speeds corresponding to ~67, 75, 84 and 91% shod VO2max respectively, separated by a 1 minute rest. After the 4th stage treadmill speed was incremented by 0.1 km·h(-1) every 15 s until participants reached volitional exhaustion.

RESULTS

RE was improved by 4.4±7.0% across intensities in the barefoot condition (P=0.040). The improvement in RE was related to removed shoe mass (r2=0.80, P=0.003) with an intercept at 0% improvement for RE at 0.520 kg total shoe mass. Both vVO2max (by 4.5±5.0%, P=0.048) and vmax (by 3.9±4.0%, P=0.030) also improved but VO2max was unchanged (p=0.747).

CONCLUSION

Barefoot running improves RE at high exercise intensities and increases vVO2max and vmax, but further research is required to clarify the influence of very light shoe weights on RE.

Spraying with 0.20% L-menthol does not enhance 5 km running performance in the heat in untrained runners

BACKGROUND

L-Menthol stimulates cutaneous thermoreceptors and induces cool sensations improving thermal comfort but has also been linked to heat storage responses. Therefore, L-Menthol application could lead to a conflict in behavioural and thermoregulatory drivers improving comfort but leading to a higher rate of deep body temperature rise; the present study examined this possibility.

METHODS

Six untrained male participants (age 21 [1] years; height 1.80 [0.07] m; mass 78.9 [6.9] kg; surface area 1.98 [0.13] m2) took part. They completed three trials in hot conditions (34 °C) where their clothing was sprayed (CONTROL-SPRAY or MENTHOL-SPRAY) or not sprayed (CONTROL) after a fixed intensity exercise period (15-minutes), which induced thermal discomfort, before completing a 5 km treadmill time trial (TT). Thermal perception (thermal sensation and comfort; TS, TC), thermal responses (aural temperature [Tau], skin temperature [Tskin]), perceived exertion (RPE), heart rate, pacing (1 km split time) and performance (TT completion time) were measured.

RESULTS

MENTHOL-SPRAY induced improvements in TS (up to 3 km of TT) and TC (up to 1 km) with Tau showing a tendency to be higher than CONTROL-SPRAY (+0.20 [0.29] °C) and CONTROL condition (0.30 [0.34] °C); this was not statistically significant and the rate of rise in Tau was linear. Tau was continuing to rise between the 4th and 5th kilometre of the TT. The other variables were unchanged. TT completion time and pace were not different: CONTROL 27.92 [1.65], CONTROL-SPRAY 28.10 [1.12], MENTHOL-SPRAY 27.53 [2.85] minutes.

CONCLUSION

Spraying L-MENTHOL prior to exercise in the heat culminated in improved perception but not altered performance.

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.

Habituation of the cold shock response may include a significant perceptual component

INTRODUCTION

Accidental immersion in cold water is a risk factor for many occupations. Habituation to cold-water immersion (CWI) is one practical means of reducing the cold shock response (CSR) on immersion. We investigated whether repeated thermoneutral water immersion (TWI) induced a perceptual habituation (i.e., could lessen perceived threat and anxiety) and consequently reduce the CSR on subsequent CWI.

METHODS

There were 12 subjects who completed seven 7-min head-out immersions. Immersions one and seven were CWls [15.0 (0.1) degrees C], and immersions two to six were TWI [34.9 (0.10) degrees C]. Anxiety 120-cm visual analogue scale) and the cardiorespiratory responses [heart rate (f(C)), respiratory frequency (f(R)), tidal volume (V(T)), and minute ventilation (V(E))] to immersion were measured throughout. Data were compared within subject between conditions using ANOVA to an alpha level of 0.05.

RESULTS

Acute anxiety was significantly reduced after repeated exposure to the immersion scenario (i.e., TWI): CWI-1: 6.3 (4.4) cm; and CWI-2: 4.5 (4.0) cm [condition mean (SD)]. These differences did not influence the peak in the CSR. The f(C), f(R), and V(E) responses were similar between CWI-1 and CWI-2. V(T) response was significantly lower in CWI-2; mean (SD) across the immersion: CWI-1 1.27 (0.17) vs. CWI-2 1.11 0.21 L.

DISCUSSION

Repeated TWI lessened the anxiety associated with CWI (perceptual habituation). This had a negligible effect on the primary components of the CSR, but did lower VT, which may reduce the volume of any aspirated water in an emergency situation. Reducing the threat appraisal of an environmental stressor may be a useful biproduct of survival training, thereby minimizing psychophysiological strain.

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.

Responses to sudden cold-water immersion in inexperienced swimmers following training

BACKGROUND

When suddenly immersed in cold water, humans typically exhibit the cold shock response, although training can attenuate hyperventilation. This study extends previous findings by considering the influence of physical activity to maintain buoyancy and subsequent swimming performance.

METHODS

Six inexperienced swimmers (three men and three women; mean age 22.8) received 1 wk of cold-water head-out immersions (10 x 3 min at 15 degrees C) alongside mental skills training to improve their treading water technique and to control hyperventilation upon immersion. Six inexperienced control swimmers (four men and two women; mean age 21.8) received immersions in temperate water (27 degrees C). Ventilation, brain blood flow velocity, and blood oxygenation were measured during a physiological test in which participants trod water for 150 s. In a subsequent simulated survival test, performance (swimming duration and distance) and perception of effort were recorded. All the tests were in 10 degrees C water with the head out.

RESULTS

There were significant improvements in the intervention group's ability to suppress rapid increases in respiratory frequency; 62 +/- 24 breaths x min(-1) to 33 +/- 12. The drop in brain blood flow was smaller and more transient than that previously reported due to the hypertensive response associated with treading water.

DISCUSSION

Inexperienced swimmers could benefit from cold-water habituation combined with mental skills training in order to improve voluntary control over the respiratory portion of the cold shock response as part of learning to tread water. This may improve survival prospects in a real-life emergency scenario such as an overturned boat.

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.

Habituation of the metabolic and ventilatory responses to cold-water immersion in humans

An experiment was undertaken to answer long-standing questions concerning the nature of metabolic habituation in repeatedly cooled humans. It was hypothesised that repeated skin and deep-body cooling would produce such a habituation that would be specific to the magnitude of the cooling experienced, and that skin cooling alone would dampen the cold-shock but not the metabolic response to cold-water immersion. Twenty-one male participants were divided into three groups, each of which completed two experimental immersions in 12°C water, lasting until either rectal temperature fell to 35°C or 90min had elapsed. Between these two immersions, the control group avoided cold exposures, whilst two experimental groups completed five additional immersions (12°C). One experimental group repeatedly immersed for 45min in average, resulting in deep-body (1.18°C) and skin temperature reductions. The immersions in the second experimental group were designed to result only in skin temperature reductions, and lasted only 5min. Only the deep-body cooling group displayed a significantly blunted metabolic response during the second experimental immersion until rectal temperature decreased by 1.18°C, but no habituation was observed when they were cooled further. The skin cooling group showed a significant habituation in the ventilatory response during the initial 5min of the second experimental immersion, but no alteration in the metabolic response. It is concluded that repeated falls of skin and deep-body temperature can habituate the metabolic response, which shows tissue temperature specificity. However, skin temperature cooling only will lower the cold-shock response, but appears not to elicit an alteration in the metabolic response.

Influence of competition on performance and pacing during cycling exercise

PURPOSE

The study's purpose was to examine the influence of head-to-head (HH) competition on performance, pacing strategy, and bioenergetics during a 2000-m cycling task.

METHODS

Fourteen participants completed three 2000-m familiarization time trials (TTs) on a Velotron cycle ergometer, before completing an additional TT and a 2000-m simulated HH competition in a counterbalanced order. During the trials, a computer-generated image of the participants completing the 2000-m course was projected onto a screen positioned in front of the participants. Although participants believed they were competing against another individual during the HH competition, they were in fact competing against their best familiarization performance (FAM), replayed on the screen by the Velotron software.

RESULTS

Performance was significantly faster in HH than in FAM or TT (184.6 ± 6.2, 187.7 ± 8.2, and 188.3 ± 9.5 s, respectively). Pacing profile in HH initially matched the FAM performance but was better maintained from 1000 m until the end of exercise. The higher power output during the latter part of the test was achieved by a greater anaerobic energy contribution, whereas the aerobic energy yield remained unchanged.

CONCLUSIONS

HH competition encourages participants to increase their performance. This occurs primarily via an increased anaerobic energy yield, which seems to be centrally mediated, and is consistent with the concept of a physiologic reserve.

Cycling cadence affects heart rate variability

The purpose of this study was to examine the effect different cycling cadences have on heart rate variability (HRV) when exercising at constant power outputs. Sixteen males had ECG and respiratory measurements recorded at rest and during 8, 10 min periods of cycling at four different cadences (40, 60, 80 and 100 revs min(-1)) and two power outputs (0 W (unloaded) and 100 W (loaded)). The cycling periods were performed following a Latin square design. Spectral analyses of R-R intervals by fast Fourier transforms were used to quantify absolute frequency domain HRV indices (ms(2)) during the final 5 min of each bout, which were then log transformed using the natural logarithm (Ln). HRV indices of high frequency (HF) power were reduced when cadence was increased (during unloaded cycling (0 W) log transformed HF power decreased from a mean [SD] of 6.3 [1.4] Ln ms(2) at 40 revs min(-1) to 3.9 [1.3] Ln ms(2) at 100 revs min(-1)). During loaded cycling (at 100 W), the low to high frequency (LF:HF) ratio formed a 'J' shaped curve as cadence increased from 40 revs min(-1) (1.4 [0.4]) to 100 revs min(-1) (1.9 [0.7]), but dipped below the 40 revs min(-1) values during the 60 revs min(-1) 1.1 (0.3) and 80 revs min(-1) 1.2 (0.6) cadence conditions. Cardiac frequency (f(C)) and ventilatory variables were strongly correlated with frequency domain HRV indices (r = -0.80 to -0.95). It is concluded that HRV indices are influenced by both cycling cadence and power output; this is mediated by the f(C) and ventilatory changes that occur as cadence or exercise intensity is increased. Consequently, if HRV is assessed during exercise, both power output/exercise intensity and cadence should be standardized.

Performance of emergency underwater breathing systems in cool (25 degrees C) and cold (12 degrees C) water

INTRODUCTION

The shortfall between breath-hold time on cold-water immersion and the time required to make an underwater escape from a helicopter provides the rationale for emergency underwater breathing systems (EUBS) for passengers flying over cold water. This study compared three types of EUBS: a compressed gas system (CG); a rebreather system (RB); and a hybrid system (H).

METHODS

Each EUBS was examined during water deployment (W(dep)) and over 90 s in cool (25 degrees C) and cold water (12 degrees C) immersion to the neck (Imm) and submersion (Subm). Subjects wore standardized clothing, including dry suit. Measures included: W(dep) time, stay time (Imm and Subm), dyspnea rating, O2 and CO2 remaining in rebreather bags [H and RB (partial pressure mmHg)], and gas volume used (CG).

RESULTS

Mean data show W(dep) was slowest in the H (17.7 s) compared to the RB (10.0 s) and CG (8.1 s). Stay time was greatest in the H (90.0 s) compared to the RB (68.3 s) and CG (87.0 s); stay time in CG was also greater than RB. Dyspnea ratings were greater in RB trials (6.5 cm) compared to the CG (2.4 cm) and H (1.9 cm). Across devices, stay time in cold water was shorter during submersion than immersion (85.9 s vs. 70.1 s). During submersion stay time was shorter in cold compared to cool water (12 degrees C: 62.8 s; 25 degrees C: 77.5 s).

DISCUSSION

The data suggest that the CG and H devices outperformed the RB device, but the H device required longer to deploy.

'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 (FIO2 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.

A motivational music and video intervention improves high-intensity exercise performance

Music and video are utilised by recreational gym users to enhance their exercise experience. Music and video have not been investigated for their combined ergogenic effect during high intensity exercise. To induce fatigue, this study was performed in warm (~26°C), moist conditions (~50%RH). Six, non-acclimated, male participants took part in the study. Each participant completed three 30-minute exercise bouts on a motorised treadmill under three counterbalanced conditions on separate days: control (CON), motivational music plus video intervention (M), non-motivational intervention (NM). They completed a warm-up (5 km·h(-1) [5 minutes], 9km·h(-1) [10 minutes]) followed by a maximal effort run (15 minutes). Participants did not receive any feedback of time elapsed, distance run or speed.

MEASURES

Distance covered (metres), heart rate, blood lactate accumulation (B(lac)) and ratings of perceived exertion (RPE). Participants in the M condition ran significantly further than in the NM (M: 3524 [388]metres; NM: 3110 [561]metres; CON: 3273 [458]metres) and CON conditions, accumulated more B(lac), but did not increase their peak RPE rating (p < 0.05). The M intervention improved tolerance of high intensity exercise in warm conditions. It was proposed that a change in attentional processing from internal (physical sensations) to external perspective (music and video) may have facilitated this improvement. These findings have strong implications for improving health, fitness and engagement in gym-based exercise programs. Key pointsThe study examined the ergogenic effect of a motivational (M) video and music intervention on high-intensity exercise performance in comparison to a non-motivational (NM) condition and a control (CON).PARTICIPANTS IN THE M CONDITION RAN SIGNIFICANTLY FURTHER THAN IN THE NM (M: 3524 [388]metres; NM: 3110 [561]metres; CON: 3273 [458]metres) and CON conditions, accumulated more B(lac), but did not increase their peak RPE rating (p < 0.05).It was proposed that a change in attentional processing from internal (physical sensations) to external perspective (music and video) may have facilitated this improvement.These findings have strong implications for improving health, fitness and engagement in gym-based exercise programs.

Psychological skills training improves exercise performance in the heat

INTRODUCTION

Fatigue occurs earlier when working at corresponding exercise intensities in hot compared with cool conditions. Psychological skills training (PST) can modify the responses evoked by thermal stimuli such as the respiratory responses on immersion to cold water. This study tested the hypothesis that a 4-d PST package would significantly increase the distance covered during 90 min of running in the heat.

METHOD

Eighteen subjects completed three maximal-effort runs (R1, R2, R3) of 90 min in the heat (30 degrees C; 40% RH). After R2, subjects were matched and randomly allocated to either a control group (CG) or psychological skills group (PSG). Between R2 and R3, the CG (N = 8) continued their normal activities, and the PSG (N = 10) received PST to help them tolerate unpleasant sensations arising from exercising in the heat, and to suppress the temptation to lower their work intensity. Key measures include distance covered, .VO2, skin (T(sk)) and aural temperature (T(au)), RPE, sweat production and evaporation, interleukin-6 (IL-6), and prolactin (PRL) in whole blood.

RESULTS

The distances covered in the CG did not differ between runs. In the PSG, there were no differences in the distance run between R1 and R2, but they ran significantly farther in R3 (8%; 1.15 km); there were no between-group differences. There were no significant differences between R1 and R3 in peak T(au), T(sk), sweat volumes, IL-6, and PRL (P > 0.05) in either group.

CONCLUSION

PST suppressed the temptation to reduce exercise intensity during R3. It is concluded that PST can improve running performance in the heat. The precise mechanisms underpinning these improvements are unclear; however, their implications for unblinded experimental design are not.

Breath-hold time during cold water immersion: effects of habituation with psychological training

INTRODUCTION

The loss of the conscious control of respiration on whole body cold water immersion (CWI) can result in the aspiration of water and drowning. Repeated CWI reduces the respiratory drive evoked by CWI and should prolong breath-hold time on CWI (BHmax(CWI)). Psychological skills training (PST) can also increase BHmax(CWI) by improving the ability of individuals to consciously suppress the drive to breathe. This study tested the hypothesis that combining PST and repeated CWI would extend BHmax(CWI) beyond that seen following only repeated CWI.

METHODS

There were 20 male subjects who completed two 2.5-min, head-out breath-hold CWI (BH1 and BH2) in water at 12 degrees C. Following BH1, subjects were matched on BHmax(CWI) and allocated to a habituation (HAB) group or a habituation plus PST group (H+PST). Between BH1 and BH2 both experimental groups undertook five 2.5-min CWI on separate days, during which they breathed freely. The H+PST also received psychological training to help tolerate cold and suppress the drive to breathe on immersion to extend BHmax(CWI).

RESULTS

During BH1, mean BHmax(CWI) (+/- SD) in the HAB group was 22.00 (10.33) s and 22.38 (10.65) s in the H+PST. After the five free-breathing CWI, both groups had a longer BHmax(CWI) in BH2. The HAB group improved by 14.13 (20.21) s, an increase of 73%. H+PST improved by 26.86 (24.70) s, a 120% increase. No significant differences were identified between the groups.

CONCLUSION

Habituation significantly increases BHmax on CWI, the addition of PST did not result in statistically significant improvements in BHmax(CWI), but may have practical significance.

Breath-hold performance during cold water immersion: effects of psychological skills training

INTRODUCTION

Accidental cold water immersion (CWI) is a significant cause of death, particularly in those who are immersed in rough water or forcibly submerged such as in a ditched and inverted helicopter. The marked reduction in maximal breath-hold time associated with CWI, part of the 'cold shock' response, significantly increases the risk of drowning. However, the response is highly variable between subjects. This experiment tested the hypothesis that part of this variability is due to psychological factors.

METHODS

There were 32 subjects who completed 2 2.5-min, head-out immersions in 11 degrees C water, separated by 7 d. Between immersions, subjects were matched on initial maximum breath-hold time on immersion (BHwater) and allocated to either a psychological intervention group (PIG) or control group (CG). PIG (n=16) subjects each undertook a psychological skills intervention comprising 4 interlinked training sessions covering goal-setting, arousal regulation, mental imagery, and positive self-talk; CG (n=16) continued normal daily activity.

RESULTS

Psychological intervention significantly increased BHwater on immersion in the PIG vs. the CG [mean (SD); CG BHwater immersion 1:24.01 (6.72) s; immersion 2: 21.34 (16.31) s; PIG: BHwater immersion 1: 24.66 (14.60) s; immersion 2: 44.25 (31.63) s]. The difference in maximum voluntary BHwater between immersion 1 and 2 in the PIG averaged 19.59 s, equating to an 80% increase following psychological intervention.

CONCLUSION

Psychological influences may account for a significant amount of the variability in the respiratory responses during CWI, and may be a key factor in determining the chances of survival following accidental immersion.