Effect of wearing an ice cooling jacket on repeat sprint performance in warm/humid conditions

Performance Benefits of Pre- and Per-cooling on Self-paced Versus Constant Workload Exercise: A Systematic Review and Meta-analysis

BACKGROUND AND OBJECTIVE

Exercise in hot environments impairs endurance performance. Cooling interventions can attenuate the impact of heat stress on performance, but the influence of an exercise protocol on the magnitude of performance benefit remains unknown. This meta-analytical review compared the effects of pre- and per-cooling interventions on performance during self-paced and constant workload exercise in the heat.

METHODS

The study protocol was preregistered at the Open Science Framework ( https://osf.io/wqjb3 ). A systematic literature search was performed in PubMed, Web of Science, and MEDLINE from inception to 9 June, 2023. We included studies that examined the effects of pre- or per-cooling on exercise performance in male individuals under heat stress (> 30 °C) during self-paced or constant workload exercise in cross-over design studies. Risk of bias was assessed using the Cochrane Risk of Bias Tool for randomized trials.

RESULTS

Fifty-nine studies (n = 563 athletes) were identified from 3300 records, of which 40 (n = 370 athletes) used a self-paced protocol and 19 (n = 193 athletes) used a constant workload protocol. Eighteen studies compared multiple cooling interventions and were included more than once (total n = 86 experiments and n = 832 paired measurements). Sixty-seven experiments used a pre-cooling intervention and 19 used a per-cooling intervention. Average ambient conditions were 34.0 °C [32.3-35.0 °C] and 50.0% [40.0-55.3%] relative humidity. Cooling interventions attenuated the performance decline in hot conditions and were more effective during a constant workload (effect size [ES] = 0.62, 95% confidence interval [CI] 0.44-0.81) compared with self-paced exercise (ES = 0.30, 95% CI 0.18-0.42, p = 0.004). A difference in performance outcomes between protocols was only observed with pre-cooling (ES = 0.74, 95% CI 0.50-0.98 vs ES = 0.29, 95% CI 0.17-0.42, p = 0.001), but not per-cooling (ES = 0.45, 95% CI 0.16-0.74 vs ES = 0.35, 95% CI 0.01-0.70, p = 0.68).

CONCLUSIONS

Cooling interventions attenuated the decline in performance during exercise in the heat, but the magnitude of the effect is dependent on exercise protocol (self-paced vs constant workload) and cooling type (pre- vs per-cooling). Pre-cooling appears to be more effective in attenuating the decline in exercise performance during a constant workload compared with self-paced exercise protocols, whereas no differences were found in the effectiveness of per-cooling.

Consideration on size, velocity and path of droplets emitted during running

BACKGROUND

People began to wear face masks during physical activities due to spread of COVID-19. There are no previous studies about the need for wearing masks while running.

METHODS

Assuming a citizen runner who runs full marathon in 4 hours, we verified the path and the amount of droplet dispersal, setting a humanoid mannequin with a mask in simulated running environment (Experiment 1). We also had six adults exercise in the same environment to examine droplet behaviors when not wearing a face mask (Experiment 2). Average droplet size was determined, and repeated measures ANOVA was carried out to examine statistical significance. To evaluate observed droplet behaviors, theoretical solutions of the downfall motion of large droplets were then derived, taking air resistance into consideration.

RESULTS

Experiment 1: wearing a face mask caused more droplets to adhere to the face; Experiment 2: droplets were emitted in conversation, coughing or sneezing, and they fell within social distancing. Average droplet size was not sensitive to the wind velocity. It could vary with a significant difference for time and wind velocity. Observed velocity and path of droplet can be expressed by the theoretical solutions.

CONCLUSIONS

Velocity and path of large droplets can be expressed by the theoretical solution of particles in downfall motion under air resistance. We therefore conclude that wearing a mask while running gives adverse effects in preventing infection. Possibility of droplet transmission while running is considered low even when not wearing a face mask, as long as social distancing is ensured.

Personal Cooling Garments: A Review

Thermal comfort is of critical importance to people during hot weather or harsh working conditions to reduce heat stress. Therefore, personal cooling garments (PCGs) is a promising technology that provides a sustainable solution to provide direct thermal regulation on the human body, while at the same time, effectively reduces energy consumption on whole-building cooling. This paper summarizes the current status of PCGs, and depending on the requirement of electric power supply, we divide the PCGs into two categories with systematic instruction on the cooling materials, working principles, and state-of-the-art research progress. Additionally, the application fields of different cooling strategies are presented. Current problems hindering the improvement of PCGs, and further development recommendations are highlighted, in the hope of fostering and widening the prospect of PCGs.

Ice slurry ingestion improves physical performance during high-intensity intermittent exercise in a hot environment

Ice slurry ingestion enhances exercise performance by lowering the core body temperature. However, an operational issue related to this ingestion is the requirement for a high intake of 7.5 g·kg^-1 to produce the desired effects. We investigated the effects of the intake of low amounts of ice slurry at −2°C on the tympanic temperature and exercise performance during repeated high-intensity intermittent exercises in a hot environment. This study was a randomized, crossover study, with a 6-day washout period. Twelve university rugby union players performed two 30-min sessions of high-intensity intermittent exercises separated by a 15-min half-time break on a cycle ergometer in a hot environment (28.8°C ± 0.1°C, 49.5% ± 0.6% relative humidity). The participants ingested 450 g of −2°C-ice slurry (ICE), or a 30°C-beverage (CON) having the same composition as ICE, or 30°C-water (WAT) during the half-time break. The tympanic temperature and skin temperature were measured as the physiological data, and the peak power and mean power as the exercise performance data. The tympanic temperature at the half-time break and beginning of the 2^nd session was significantly lower in the ICE group as compared with the CON and WAT groups. The skin temperature at the half-time break was significantly lower in the ICE group as compared with the WAT group. While the peak power and mean power during the 2^nd session were significantly greater in the ICE group as compared with the CON and WAT groups. Our findings suggest that even the intake of lower amounts, as compared with those used in previous studies, of low-temperature ice slurry can reduce the body temperature and improve the peak power. These results suggest that intake of low-temperature ice slurry as a strategy for internal body cooling is useful for improving endurance exercise performance in hot environments.

Exogenous Ketone Salt Supplementation and Whole-Body Cooling Do Not Improve Short-Term Physical Performance

Exogenous ketone supplementation and whole-body cooling (WBC) have shown to independently influence exercise metabolism. Whether readily available ketone salts, with and without WBC, would provide similar metabolic benefits during steady-state aerobic and time-trial performances was investigated. Nine active males (VO_2peak: 56.3 ± 2.2 mL·kg⁻¹·min⁻¹) completed three single-blind exercise sessions preceded by: (1) ingestion of placebo (CON), (2) ketone supplementation (0.3 g·kg⁻¹ β-OHB) (KET), and (3) ketone supplementation with WBC (KETCO). Participants cycled in steady-state (SS, 60% W_max) condition for 30-min, immediately followed by a 15-min time trial (TT). Skin and core temperature, cardio-metabolic, and respiratory measures were collected continuously, whereas venous blood samples were collected before and after supplementation, after SS and TT. Venous β-OHB was elevated, while blood glucose was lower, with supplementation vs. CON (p < 0.05). TT power output was not different between conditions (p = 0.112, CON: 190 ± 43.5 W, KET: 185 ± 40.4 W, KETCO: 211 ± 50.7 W). RER was higher during KETCO (0.97 ± 0.09) compared to both CON (0.88 ± 0.04, p = 0.012) and KET (0.88 ± 0.05, p = 0.014). Ketone salt supplementation and WBC prior to short-term exercise sufficiently increase blood β-OHB concentrations, but do not benefit metabolic shifts in fuel utilization or improve time trial performance.

Cooling efficiency of vests with different cooling concepts over 8-hour trials

As frequency and severity of heat waves are increasing, personal cooling systems are being considered as a tool to mitigate heat strain in workers in various occupational settings. This study assessed cooling capacities (C; W·h·m^-2) of various commercially available vests using different cooling concepts. Measurements were conducted over 8 h in a climatic chamber (Ta: 35 °C, RH: 35 %) using a thermal manikin (Ts: 35 °C). Cooling power (P) and duration of efficient cooling (t_c) determined the C value of each vest. Among the cooling concepts the active cooling vests were the most efficient, extracting 331 W·h·m^-2, followed by the vests with phase change material (PCM) inserts, hybrid and evaporative vests, extracting a maximum of 164 W·h·m^-2, 146 W·h·m^-2 and 113 W·h·m^-2, respectively. While some vests with PCM inserts provided intense but shorter cooling, evaporative vests provided mild but longer cooling throughout. Practitioner summary: The study assessed the cooling capacity of commercially available vests, using a thermal manikin. The vests present an affordable solution in various occupational settings where air-conditioning is not an option. A range of cooling capacities among different cooling concepts and vests of the same category were noted. Abbreviations: ACVs: air-cooled vests; LCVs: liquid-cooled vests; ECVs: evaporative cooling vests; HCVs: hybrid cooling vests; PCVs: phase-change cooling vests; PCM: phase change material; C: cooling capacity; Rt: thermal resistance; Re: evaporative resistance; Re (%): relative evaporative resistance; P: cooling power; P_max: maximal cooling power; P_avg: average cooling power; t_c: cooling duration; AUC: area under the curve; Ta: ambient temperature; RH: relative humidity; v_a: chamber air flow; Ts: manikin surface temperature.

Cooling Between Exercise Bouts and Post-exercise With the Fan Cooling Jacket on Thermal Strain in Hot-Humid Environments

This study investigated the effects of cooling between exercise bouts and post-exercise with a commercially available fan cooling jacket on thermal and perceptual responses during and following exercise in hot-humid environments. Ten male athletes completed two 30 min cycling bouts at a constant workload (1.4 watts⋅kg^-1 of body mass) with a 5 min recovery period in between. Exercise was followed by a 10 min recovery period. In an environmental chamber (33°C, 65% relative humidity), participants performed two trials with (FCJ) or without (CON) the fan cooling jacket on a T-shirt during the 5 min inter-exercise and 10 min post-exercise recovery periods. Mean, chest and upper arm skin temperatures, and thermal sensation and comfort were lower in FCJ than CON trial during and following exercise (P < 0.05). Thigh and calf skin temperatures, infrared tympanic temperature and heart rate were lower in FCJ than CON trial during the experimental trials (P < 0.05). The rates of fall in mean, chest and upper arm skin temperatures, infrared tympanic temperature and thermal sensation and comfort were faster in FCJ than CON trial during both recovery periods (P < 0.05). There were faster rates of fall in thigh and calf skin temperatures and heart rate in FCJ than CON trial during the post-exercise recovery period (P < 0.05). No difference was observed between trials in the rating of perceived exertion (P > 0.05). This study indicates that cooling between exercise bouts and post-exercise with the fan cooling jacket would effectively mitigate thermal strain and perception/discomfort during and following exercise in hot-humid environments. This garment would reduce whole-body skin temperature quickly while promoting falls in lower-body as well as upper-body skin temperatures.

A Matter of Degrees: A Systematic Review of the Ergogenic Effect of Pre-Cooling in Highly Trained Athletes

The current systematic review evaluated the effects of different pre-cooling techniques on sports performance in highly-trained athletes under high temperature conditions. PubMed/MEDLINE, EMBASE, Web of Science, CENTRAL, Scopus, and SPORTDiscus databases were searched from inception to December 2019. Studies performing pre-cooling interventions in non-acclimatized highly-trained athletes (>55 mL/kg/min of maximal oxygen consumption) under heat conditions (≥30 °C) were included. The searched reported 26 articles. Pre-cooling techniques can be external (exposure to ice water, cold packs, or cooling clothes), internal (intake of cold water or ice), or mixed. Cooling prior to exercise concluded increases in distance covered (1.5-13.1%), mean power output (0.9-6.9%), time to exhaustion (19-31.9%), work (0.1-8.5%), and mean peak torque (10.4-22.6%), as well as reductions in completion time (0.6-6.5%). Mixed strategies followed by cold water immersion seem to be the most effective techniques, being directly related with the duration of cooling and showing the major effects in prolonged exercise protocols. The present review showed that pre-cooling methods are an effective strategy to increase sports performance in hot environments. This improvement is associated with the body surface exposed and its sensibility, as well as the time of application, obtaining the best results in prolonged physical exercise protocols.

A novel vest with dual functions for firefighters: combined effects of body cooling and cold fluid ingestion on the alleviation of heat strain

This study investigated the separate and combined effects of skin cooling and cold fluid ingestion on the alleviation of heat strain when wearing protective firefighting clothing at an air temperature of 30°C with 50%RH. A vest with the dual functions of cooling and providing sports drink supply (1.2% body mass) was developed. Eight males participated in the following four conditions: control [CON], drinking only [DO], cooling only [CO], and both cooling and drinking [CD]. The results showed that rectal (T_re), mean skin temperature (T_sk) and heart rate (HR) during recovery were lower for CD than for CON (p<0.05), while no significant differences between the four conditions were found during exercise. CO significantly reduced mean T_sk and HR and improved thermal sensation, whereas DO was effective for relieving thirst and lowering HR in recovery. In summary, the combined effect of skin cooling and fluid ingestion was synergistically manifested in T_re, T_sk and thermal sensation in recovery.Practitioner Summary: The present results provide data on a novel vest that contributes to alleviating firefighters' heat strain. Because a cooling vest after melting may be a burden for firefighters, this study indicates a practical way to reduce the additional weight load of the vest by drinking the melted fluid of the cooling packs.

Translating Science Into Practice: The Perspective of the Doha 2019 IAAF World Championships in the Heat

Hot and humid ambient conditions may play a major role during the endurance events of the 2019 IAAF world championships, the 2020 summer Olympics and many other sports events. Here, various countermeasures with scientific evidence are put in perspective of their practical application. This manuscript is not a comprehensive review, but rather a set of applied recommendations built upon sound scientific reasoning and experience with elite athletes. The primary recommendation for an athlete who will be competing in the heat, will be to train in the heat. This acclimatization phase should last for 2 weeks and be programmed to accommodate the taper and travel requirements. Despite extensive laboratory-based research, hydration strategies within athletics are generally dictated by the race characteristics. The main opportunities for hydration are during the preparation and recovery phases. In competition, depending on thirst, feeling, and energy requirements, water may be ingested or poured. The athletes should also adapt their warm-up routines to the environmental conditions, as it may do more harm than good. Avoiding harm includes limiting unnecessary heat exposure before the event, warming-up with cooling aids such as ice-vest or cold/iced drinks, and avoiding clothing or accessories limiting sweat evaporation. From a medical perspective, exertional heat stroke should be considered immediately when an athlete collapses or struggles during exercise in the heat with central nervous system disorders. Once a rectal temperature >40.5°C is confirmed, cooling (via cold water immersion) should be undertaken as soon as possible (cool first/transport second).

Is active recovery during cold water immersion better than active or passive recovery in thermoneutral water for postrecovery high-intensity sprint interval performance?

High-intensity exercise is impaired by increased esophageal temperature (T_es) above 38 °C and/or decreased muscle temperature. We compared the effects of three 30-min recovery strategies following a first set of three 30-s Wingate tests (set 1), on a similar postrecovery set of Wingate tests (set 2). Recovery conditions were passive recovery in thermoneutral (34 °C) water (Passive-TN) and active recovery (underwater cycling; ∼33% maximum power) in thermoneutral (Active-TN) or cold (15 °C) water (Active-C). T_es rose for all conditions by the end of set 1 (∼1.0 °C). After recovery, T_es returned to baseline in both Active-C and Passive-TN but remained elevated in Active-TN (p < 0.05). At the end of set 2, T_es was lower in Active-C (37.2 °C) than both Passive-TN (38.1 °C) and Active-TN (38.8 °C) (p < 0.05). From set 1 to 2 mean power did not change with Passive-TN (+0.2%), increased with Active-TN (+2.4%; p < 0.05), and decreased with Active-C (-3.2%; p < 0.05). Heart rate was similar between conditions throughout, except at end-recovery; it was lower in Passive-TN (92 beats·min^-1) than both exercise conditions (Active-TN, 126 beats·min^-1; Active-C, 116 beats·min^-1) (p < 0.05). Although Active-C significantly reduced T_es, the best postrecovery performance occurred with Active-TN. Novelty An initial set of 3 Wingates increased T_es to ∼38 °C. Thirty minutes of Active-C was well tolerated, and decreased T_es and blood lactate to baseline values, but decreased subsequent Wingate performance.

Hand and torso pre-cooling does not enhance subsequent high-intensity cycling or cognitive performance in heat

The purpose of this study was to compare the separate and combined effects of two practical cooling methods (hand and torso) used prior to exercise on subsequent high-intensity cycling performance in heat. Ten trained male cyclists (V̇O2peak: 65.7 ± 10.7 ml.kg-1.min-1) performed four experimental trials (randomised within-subjects design) involving 30-min of pre-cooling (20-min seated; PRE-COOL, 10 min warm-up; PRE-COOL+WUP), while using a: (1) hand-cooling glove (CG); (2) cooling jacket (CJ); (3) both CG and CJ (CG+J); or (4) no-cooling (NC) control, followed by a cycling race simulation protocol (all performed in 35.0 ± 0.6°C and 56.6 ± 4.5% RH). During the 30-min of pre-cooling, no reductions in core (Tc) or mean skin temperature (Tsk) occurred; however, Tsk remained lower in the CJ and CG+J trials compared to NC and CG (p = 0.002-0.040, d= 0.55-1.01). Thermal sensation ratings also indicated that participants felt "hotter" during NC compared to all other trials during both PRE-COOL and PRE-COOL+WUP (p = 0.001-0.015, d= 1.0-2.19), plus the early stages of exercise (sets 1-2; p = 0.005-0.050, d= 0.56-1.22). Following cooling, no differences were found for absolute Tc and Tsk responses between trials over the entire exercise protocol (p > 0.05). Exercise and cognitive (working memory) performance also did not differ between trials (p = 0.843); however, cognitive performance improved over time in all trials (p < 0.001). In summary, pre-cooling (20-min seated and 10-min warm-up) in heat did not improve subsequent high-intensity cycling performance, cognitive responses and associated thermoregulatory strain (Tc and Tsk) compared to control.

Practical Torso Cooling During Soccer-Specific Exercise in the Heat

CONTEXT

Precooling and midevent cooling of the torso using cooling vests can improve exercise performance in the heat with or without physiological changes; however, the effects of such cooling during intermittent exercise in the heat are unknown.

OBJECTIVE

To investigate the effects of torso cooling during intermittent exercise in the heat (35°C, 50% relative humdity) on sprint performance and the physiological and perceptual responses to the exercise.

DESIGN

Crossover study.

SETTING

Walk-in environmental chamber.

PATIENTS OR OTHER PARTICIPANTS

Ten non-heat-acclimated, male soccer players (age = 25 ± 2 years, height = 1.77 ± 0.06 m, mass = 72.9 ± 7.6 kg).

INTERVENTION(S)

Two 90-minute bouts of soccer-specific intermittent running in the heat: 1 trial with a cooling vest worn during the exercise and 1 trial without a cooling vest. Each trial comprised two 45-minute periods separated by approximately 15 minutes of seated rest in cool conditions (approximately 23°C, 50% relative humdity).

MAIN OUTCOME MEASURE(S)

Peak sprint speed, rectal temperature (T_r), mean-weighted skin temperature (T_sk), heart rate (HR), rating of perceived exertion (RPE), and thermal sensation (TS) were measured every 5 minutes.

RESULTS

Peak sprint performance was largely unaffected by the cooling vest. The T_r, T_sk, HR, RPE, and TS were unaffected in the cooling-vest trial during the first 45 minutes, but T_r rose at a slower rate in the cooling-vest trial (0.026°C^.min^-1 ± 0.008°C^.min^-1) than in the no-vest trial (0.032°C^.min^-1 ± 0.009°C^.min^-1). During the second 45-minute period, T_r, T_r rate of rise, T_sk, RPE, and TS were lower in the cooling-vest trial (Hedges g range, 0.55-0.84), but mean HR was unaffected.

CONCLUSIONS

Wearing a cooling vest during soccer-specific intermittent running in the heat reduced physiological and perceptual strain but did not increase peak sprint speed.

Wearable Polyethylene/Polyamide Composite Fabric for Passive Human Body Cooling

Personal cooling technologies (PCTs) locally control the temperature of an individual instead of a whole building and are thus energy saving. However, most PCTs still consume energy and are heavy in weight, restricting their application among human beings. To achieve personal thermal comfort and no energy consumption on hot summer days, we designed a bilayer structure fabric with high thermal comfort by increasing the dissipation of human thermal radiation and reducing solar energy absorption simultaneously. The fabric consisted of two layers, including a polyethylene film with nanopores (100-1000 nm in pore size) and a film made of nylon 6 nanofibers (ca. 100 nm in diameter) with beads (ca. 230 nm in diameter), which could increase the visible light reflectance but not affect the infrared wave radiation. Therefore, the designed fabric showed a high heat dissipation power, which was 14.13, 17.93, and 17.93 W/m² higher than that of the selected traditional textiles of cotton, linen, and odile, respectively, suggesting good cooling capability. Its cooling performance was better than those reported by the previous research works even at a higher ambient temperature. Meanwhile, the moisture penetrability and hygroscopic property results indicated that the wearing comfort of the designed fabric reached the levels of the selected traditional textiles.

Continuous and intermittent heat acclimation and decay in team sport athletes

The aim of this study was to compare the impact of continuous (CON) and intermittent (INT) heat acclimation protocols on repeat-sprint performance, and to also assess the degree of performance decay following acclimation. Using a pair-matched, between subjects design, 16 trained male team sport athletes were allocated to either INT (8 sessions over 15 days) or CON acclimation (8 sessions over 8 days) groups. Participants performed a heat tolerance test (HTT) involving 60-min of repeat-sprint cycling with a 10-min half time break (in 35.3 ± 0.7°C, 60.1 ± 4.0%; RH) two days pre- (pre-HTT) and post-acclimation (post-HTT1). Decay was investigated with two further HTT's completed over the next two weeks (post-HTT2 and post-HTT3). Results showed the post-HTT1 performance variables [mean power (pre-HTT; INT = 1002.07 ± 173.74, CON = 1057.10 ± 180.07 / post-HTT1; INT = 1097.11 ± 186.85, CON = 1163.77 ± 184.65 W), mean power (W.kg^-1), total work (kJ) and work (J.kg^-1)] were greater than pre-HHT (p < 0.001) after acclimation, with no differences between INT and CON. No differences in final core and mean skin temperatures or heart rate existed after INT or CON acclimation, however 30 min measures for thermal sensation, perceived thirst and ratings of perceived exertion (as well as the final measure) were lower in post-HTT1 (p < 0.05) in CON. Performance and thermoregulatory responses in post-HTT2 and 3 were similar to post-HTT1 in both INT and CON. These results indicate that prolonged repeat-sprint exercise in the heat is improved after acclimation involving short, high-intensity cycling sessions using either CON or INT protocols, with performance well-maintained over the subsequent 2 weeks, despite removal of the heat stimulus.

Effects of Half-Time Cooling Using A Cooling Glove and Jacket on Manual Dexterity and Repeated-Sprint Performance in Heat

This study aimed to assess the separate and combined effects of a cooling glove (CG) and a gel-cooling jacket (CJ) used during a half-time break on manual dexterity performance (Purdue Pegboard test) and subsequent repeat-sprint cycling performance in hot conditions. Twelve male athletes performed four experimental trials (within subjects, counterbalanced design) that consisted of: wearing a CG, wearing a CJ, combination of CG and CJ (CG+J) or a no-cooling control (NC) for 15 min during a 20 min half-time break performed between 2 x 30 min repeated-sprint cycling bouts in heat (35.0 ± 1.2°C and 52.5 ± 7.4% RH). Manual dexterity (dominant and non-dominant hand) was assessed immediately before and after the first-half of exercise, then immediately after cooling and the second-half of exercise. No differences were found for manual dexterity performance between trials or over time (p > 0.05). Additionally, no differences were found for power and work performance variables assessed during the second-half of exercise (p > 0.05), however participants felt 'cooler' wearing CG+J compared to NC (Thermal Sensation scale; p = 0.041). Further, no differences were found between trials for changes in gastrointestinal core temperature for any time period assessed (p > 0.05). In conclusion, the cooling trials did not affect manual dexterity or second-half repeated-sprint cycling performance compared to NC.

Effect of a Cooling Kit on Physiology and Performance Following Exercise in the Heat

Context: Exercising in the heat leads to an increase in body temperature that can increase the risk of heat illness or cause detriments in exercise performance. Objective: To examine a phase change heat emergency kit (HEK) on thermoregulatory and perceptual responses and subsequent exercise performance following exercise in the heat. Design: Two randomized crossover trials that consisted of 30 minutes of exercise, 15 minutes of treatment (T1), performance testing (5-10-5 pro-agility test and 1500-m run), and another 15 minutes of treatment (T2) identical to T1. Setting: Outdoors in the heat (wet-bulb globe temperature: 31.5°C [1.8°C] and relative humidity: 59.0% [5.6%]). Participants: Twenty-six (13 men and 13 women) individuals (aged 20–27 y). Interventions: Treatment was performed with HEK and without HEK (control, CON) modality. Main Outcome Measures: Gastrointestinal temperature, mean skin temperature, thirst sensation, and muscle pain. Results: Maximum gastrointestinal temperature following exercise and performance was not different between trials (P > .05). Cooling rate was faster during T1 CON (0.053°C/min [0.049°C/min]) compared with HEK (0.043°C/min [0.032°C/min]; P = .01). Mean skin temperature was lower in HEK during T1 (P < .001) and T2 (P = .05). T2 thirst was lower in CON (P = .02). Muscle pain was lower in HEK in T2 (P = .03). Performance was not altered (P > .05). Conclusions: HEK improved perception but did not enhance cooling or performance following exercise in the heat. HEK is therefore not recommended to facilitate recovery, treat hyperthermia, or improve performance.

Dietetic-nutritional, physical and physiological recovery methods post-competition in team sports

To a proper recovery, is absolutely necessary to know that athletes with enhanced recovery after maximal exercise are likely to perform better in sports. Recovery strategies are commonly used in team sports despite limited scientific evidence to support their effectiveness in facilitating optimal recovery and the players spend a much greater proportion of their time recovering than they do in training. According to authors, some studies investigated the effect of recovery strategies on physical performance in team sports, lack of experimental studies about the real origin of the fatigue, certify the need for further study this phenomenon. Thus, developing effective methods for helping athletes to recover is deemed essential. Therefore, the aim of this review is provide information for his practical application, based on scientific evidence about recovery in team sports.

Effect of wrist cooling on aerobic and anaerobic performance in elite sportsmen

BACKGROUND

Body cooling has been used to increase sporting performance and enhance recovery. Several studies have reported improvement in exercise capacities using forearm and hand cooling or only hand cooling. Wrist cooling has emerged as a portable light weight solution for precooling prior to sporting activity. The Astrand test for aerobic performance and the Wingate test for anaerobic performance are reliable and accurate tests for performance assessment. This study conducted on elite Indian athletes analyses the effects of wrist precooling on aerobic and anaerobic performance as tested by the Astrand test and the Wingate test before and after wrist precooling.

METHODS

67 elite sportsmen were administered Wingate and Astrand test under standardised conditions with and without wrist precooling using a wrist cooling device (dhamaSPORT). Paired t-test was applied to study effect on aerobic [VO2 (ml/min/kg)] and anaerobic performance [peak power (W/kg) and average power (W/kg)] and Cohen's d was used to calculate effect size of wrist precooling.

RESULTS

After wrist precooling, significant increase of 0.22 (p = 0.014, 95% CI: 0.047, 0.398) in peak power (W/kg) and 0.22 (p < 0.0001, 95% CI: 0.142, 0.291) was observed in average power (W/kg). Although, an increase of 1.38 (p = 0.097, 95% CI: -0.225, 3.012) was observed in VO2 (ml/min/kg), wrist precooling was not significantly effective in aerobic performance. Wrist cooling effect size was smaller in VO2 (Cohen's d = 0.21), peak power (Cohen's d = 0.31) and it was larger in average power (Cohen's d = 0.71).

CONCLUSION

Results show wrist precooling significantly improves anaerobic than aerobic performance of elite sportsmen.

Sports and environmental temperature: From warming-up to heating-up

Most professional and recreational athletes perform pre-conditioning exercises, often collectively termed a 'warm-up' to prepare for a competitive task. The main objective of warming-up is to induce both temperature and non-temperature related responses to optimize performance. These responses include increasing muscle temperature, initiating metabolic and circulatory adjustments, and preparing psychologically for the upcoming task. However, warming-up in hot and/or humid ambient conditions increases thermal and circulatory strain. As a result, this may precipitate neuromuscular and cardiovascular impairments limiting endurance capacity. Preparations for competing in the heat should include an acclimatization regimen. Athletes should also consider cooling interventions to curtail heat gain during the warm-up and minimize dehydration. Indeed, although it forms an important part of the pre-competition preparation in all environmental conditions, the rise in whole-body temperature should be limited in hot environments. This review provides recommendations on how to build an effective warm-up following a 3 stage RAMP model (Raise, Activate and Mobilize, Potentiate), including general and context specific exercises, along with dynamic flexibility work. In addition, this review provides suggestion to manipulate the warm-up to suit the demands of competition in hot environments, along with other strategies to avoid heating-up.

Evaluating the Physiological and Perceptual Responses of Wearing a Newly Designed Cooling Vest for Construction Workers

Construction workers are subjected to heat stress because of the hot environment, physically demanding tasks, and/or personal protective equipment. A tailor-made cooling vest that protects construction workers from heat-related injuries was developed. The purpose of the study is to examine a newly designed cooling vest's effectiveness in alleviating physiological and perceptual strain in a hot and humid environment. Twelve male participants performed two trials, i.e., cooling vest (VEST) and control (CON) in a climatic chamber controlled at 37°C temperature, 60% relative humidity, 0.3 m/s air velocity, and 450 W/m2 solar radiation to simulate the summer working environment of construction sites. Two bouts of treadmill exercise intermitted with 30-minute passive recovery were designed to simulate the practical work-rest schedule of the construction industry. The cooling vest was used during the passive recovery period in the VEST condition, and the results were compared with that of no cooling vest in the CON condition. The results revealed that the newly designed cooling vest can significantly alleviate heat strain and improve thermal comfort, based on the decrease in body temperature, heart rate, and subjective perceptions (including perceived exertion, thermal, wetness, and comfort sensation) of the participants. It can also prolong work duration in the subsequent exercise. The cooling countermeasures proposed in this study will be able to provide an effective solution in situations that involve repeated bouts of outdoor construction work.

Neck Cooling Improves Table Tennis Performance amongst Young National Level Players

This study aimed to examine the effects of neck cooling on table tennis performance. Eight young, National level, male table tennis players (age 16 ± 2 years, height 1.77 ± 0.08 m, body mass 67.54 ± 10.66 kg) were recruited. Participants attended four testing sessions separated by a week. Session one determined fitness levels, and session two was a familiarisation trial. The final two sessions involved completing the table tennis-specific protocol either with (ICE) or without (CON) neck cooling for 1 min before each exercise period (bout: 80⁻90 shots), which represented an individual game. The exercise protocol required completing three bouts to represent a match, each simulating a different skill (forehand, backhand, alternate forehand and backhand), against a mechanical ball thrower. Performance was measured by the number of balls hitting two pre-determined targets. Heart rate, ratings of perceived exertion (RPE), and thermal sensation (TS) were measured. Total performance scores (shots on target) were significantly greater during ICE (136 ± 26), compared to CON (120 ± 25; p = 0.006) with a 15 (±12)% improvement. Effects for time (p < 0.05) but not condition (p > 0.05) were found for RPE and all other physiological variables. TS significantly decreased with cooling throughout the protocol (p = 0.03). Neck cooling appears to be beneficial for table tennis performance by lowering thermal sensation.

CAERvest® - a novel endothermic hypothermic device for core temperature cooling: safety and efficacy testing

INTRODUCTION

Cooling of the body is used to treat hyperthermic individuals with heatstroke or to depress core temperature below normal for neuroprotection. A novel, chemically activated, unpowered cooling device, CAERvest®, was investigated for safety and efficacy.

METHODS

Eight healthy male participants (body mass 79.9 ± 1.9 kg and body fat percentage 16.1 ± 3.8%) visited the laboratory (20 °C, 40% relative humidity) on four occasions. Following 30-min rest, physiological and perceptual measures were recorded. Participants were then fitted with the CAERvest® proof of concept (PoC) or prototype 1 (P1), 2 (P2) or 3 (P3) for 60 min. Temperature, cardiovascular and perceptual measures were recorded every 5 min. After cooling, the CAERvest® was removed and the torso checked for cold-related injuries.

RESULTS

Temperature measures significantly (p < 0.05) reduced pre to post in all trials. Larger reductions in core and skin temperatures were observed for PoC (-0.36 ± 0.18 and -1.55 ± 0.97 °C) and P3 (-0.36 ± 0.22 and -2.47 ± 0.82 °C), compared with P1 and P2. No signs of cold-related injury were observed at any stage.

CONCLUSION

This study demonstrates that the CAERvest® is an effective device for reducing body temperature in healthy normothermic individuals without presence of cold injury. Further research in healthy and clinical populations is warranted.

A Comparison of 2 Practical Cooling Methods on Cycling Capacity in the Heat

CONTEXT

Cooling the torso and neck can improve exercise performance and capacity in a hot environment; however, the proposed mechanisms for the improvements often differ.

OBJECTIVE

To directly compare the effects of cooling the neck and torso region using commercially available devices on exercise capacity in a hot environment (temperature = 35°C ± 0.1°C, relative humidity = 50.1% ± 0.7%).

DESIGN

Crossover study.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

Eight recreationally active, nonheat-acclimated men (age = 24 ± 4 years, height = 1.82 ± 0.10 m, mass = 80.3 ± 9.7 kg, maximal power output = 240 ± 25 W).

INTERVENTION(S)

Three cycling capacity tests at 60% maximal power output to volitional exhaustion: 1 with no cooling (NC), 1 with vest cooling (VC), and 1 with a neck cooling collar (CC).

MAIN OUTCOME MEASURE(S)

Time to volitional exhaustion, rectal temperature, mean skin temperature, torso and neck skin temperature, body mass, heart rate, rating of perceived exertion, thermal sensation, and feeling scale were measured.

RESULTS

Participants cycled longer with VC (32.2 ± 9.5 minutes) than NC (27. 6 ± 7.6 minutes; P = .03; d = 0.54) or CC (30.0 ± 8.8 minutes; P = .02; d = 0.24). We observed no difference between NC and CC (P = .12; d = 0.31). Neck and torso temperature and perceived thermal sensation were reduced with the use of cooling modalities (P < .001), but no other variables were affected.

CONCLUSIONS

Cycling capacity in the heat improved when participants used a commercially available cooling vest, but we observed no benefit from wearing a commercially available CC. The vest and the collar did not alter the heart rate, rectal temperature, skin temperature, or sweat-loss responses to the cycling bout.

Effects of Intermittent Neck Cooling During Repeated Bouts of High-Intensity Exercise

The purpose of this investigation was to determine the influence of intermittent neck cooling during exercise bouts designed to mimic combat sport competitions. Participants (n = 13, age = 25.3 ± 5.0 year height = 176.9 ± 7.5 cm, mass = 79.3 ± 9.0 kg, body fat = 11.8% ± 3.1%) performed three trials on a cycle ergometer. Each trial consisted of two, 5-min high-intensity exercise (HEX) intervals (HEX1 and HEX2—20 s at 50% peak power, followed by 15 s of rest), and a time to exhaustion (TTE) test. One-minute rest intervals were given between each round (RI1 and RI2), during which researchers treated the participant’s posterior neck with either (1) wet-ice (ICE); (2) menthol spray (SPRAY); or (3) no treatment (CON). Neck (T_NECK) and chest (T_CHEST) skin temperatures were significantly lower following RI1 with ICE (vs. SPRAY). Thermal sensation decreased with ICE compared to CON following RI1, RI2, TTE, and a 2-min recovery. Rating of perceived exertion was also lower with ICE following HEX2 (vs. CON) and after RI2 (vs. SPRAY). Treatment did not influence TTE (68.9 ± 18.9s). The ability of intermittent ICE to attenuate neck and chest skin temperature rises during the initial HEX stages likely explains why participants felt cooler and less exerted during equivalent HEX bouts. These data suggest intermittent ICE improves perceptual stress during short, repeated bouts of vigorous exercise.

Consensus Recommendations on Training and Competing in the Heat

Exercising in the heat induces thermoregulatory and other physiological strain that can lead to impairments in endurance exercise capacity. The purpose of this consensus statement is to provide up-to-date recommendations to optimize performance during sporting activities undertaken in hot ambient conditions. The most important intervention one can adopt to reduce physiological strain and optimize performance is to heat acclimatize. Heat acclimatization should comprise repeated exercise–heat exposures over 1–2 weeks. In addition, athletes should initiate competition and training in an euhydrated state and minimize dehydration during exercise. Following the development of commercial cooling systems (e.g., cooling vests), athletes can implement cooling strategies to facilitate heat loss or increase heat storage capacity before training or competing in the heat. Moreover, event organizers should plan for large shaded areas, along with cooling and rehydration facilities, and schedule events in accordance with minimizing the health risks of athletes, especially in mass participation events and during the first hot days of the year. Following the recent examples of the 2008 Olympics and the 2014 FIFA World Cup, sport governing bodies should consider allowing additional (or longer) recovery periods between and during events for hydration and body cooling opportunities when competitions are held in the heat.

Cooling athletes with a spinal cord injury

Cooling strategies that help prevent a reduction in exercise capacity whilst exercising in the heat have received considerable research interest over the past 3 decades, especially in the lead up to a relatively hot Olympic and Paralympic Games. Progressing into the next Olympic/Paralympic cycle, the host, Rio de Janeiro, could again present an environmental challenge for competing athletes. Despite the interest and vast array of research into cooling strategies for the able-bodied athlete, less is known regarding the application of these cooling strategies in the thermoregulatory impaired spinal cord injured (SCI) athletic population. Individuals with a spinal cord injury (SCI) have a reduced afferent input to the thermoregulatory centre and a loss of both sweating capacity and vasomotor control below the level of the spinal cord lesion. The magnitude of this thermoregulatory impairment is proportional to the level of the lesion. For instance, individuals with high-level lesions (tetraplegia) are at a greater risk of heat illness than individuals with lower-level lesions (paraplegia) at a given exercise intensity. Therefore, cooling strategies may be highly beneficial in this population group, even in moderate ambient conditions (~21 °C). This review was undertaken to examine the scientific literature that addresses the application of cooling strategies in individuals with an SCI. Each method is discussed in regards to the practical issues associated with the method and the potential underlying mechanism. For instance, site-specific cooling would be more suitable for an athlete with an SCI than whole body water immersion, due to the practical difficulties of administering this method in this population group. From the studies reviewed, wearing an ice vest during intermittent sprint exercise has been shown to decrease thermal strain and improve performance. These garments have also been shown to be effective during exercise in the able-bodied. Drawing on additional findings from the able-bodied literature, the combination of methods used prior to and during exercise and/or during rest periods/half-time may increase the effectiveness of a strategy. However, due to the paucity of research involving athletes with an SCI, it is difficult to establish an optimal cooling strategy. Future studies are needed to ensure that research outcomes can be translated into meaningful performance enhancements by investigating cooling strategies under the constraints of actual competition. Cooling strategies that meet the demands of intermittent wheelchair sports need to be identified, with particular attention to the logistics of the sport.

Consensus recommendations on training and competing in the heat

Exercising in the heat induces thermoregulatory and other physiological strain that can lead to impairments in endurance exercise capacity. The purpose of this consensus statement is to provide up-to-date recommendations to optimise performance during sporting activities undertaken in hot ambient conditions. The most important intervention one can adopt to reduce physiological strain and optimise performance is to heat acclimatise. Heat acclimatisation should comprise repeated exercise-heat exposures over 1–2 weeks. In addition, athletes should initiate competition and training in a euhydrated state and minimise dehydration during exercise. Following the development of commercial cooling systems (eg, cooling-vest), athletes can implement cooling strategies to facilitate heat loss or increase heat storage capacity before training or competing in the heat. Moreover, event organisers should plan for large shaded areas, along with cooling and rehydration facilities, and schedule events in accordance with minimising the health risks of athletes, especially in mass participation events and during the first hot days of the year. Following the recent examples of the 2008 Olympics and the 2014 FIFA World Cup, sport governing bodies should consider allowing additional (or longer) recovery periods between and during events, for hydration and body cooling opportunities, when competitions are held in the heat.

Low-frequency electrical stimulation combined with a cooling vest improves recovery of elite kayakers following a simulated 1000-m race in a hot environment

This study compared the effects of a low-frequency electrical stimulation (LFES; Veinoplus(®) Sport, Ad Rem Technology, Paris, France), a low-frequency electrical stimulation combined with a cooling vest (LFESCR ) and an active recovery combined with a cooling vest (ACTCR ) as recovery strategies on performance (racing time and pacing strategies), physiologic and perceptual responses between two sprint kayak simulated races, in a hot environment (∼32 wet-bulb-globe temperature). Eight elite male kayakers performed two successive 1000-m kayak time trials (TT1 and TT2), separated by a short-term recovery period, including a 30-min of the respective recovery intervention protocol, in a randomized crossover design. Racing time, power output, and stroke rate were recorded for each time trial. Blood lactate concentration, pH, core, skin and body temperatures were measured before and after both TT1 and TT2 and at mid- and post-recovery intervention. Perceptual ratings of thermal sensation were also collected. LFESCR was associated with a very likely effect in performance restoration compared with ACTCR (99/0/1%) and LFES conditions (98/0/2%). LFESCR induced a significant decrease in body temperature and thermal sensation at post-recovery intervention, which is not observed in ACTCR condition. In conclusion, the combination of LFES and wearing a cooling vest (LFESCR ) improves performance restoration between two 1000-m kayak time trials achieved by elite athletes, in the heat.

Thermoregulatory, cardiovascular, and perceptual responses to intermittent cooling during exercise in a hot, humid outdoor environment

Decreasing core body temperature during exercise may improve exercise tolerance, facilitate acclimatization, and prevent heat illness during summer training. We sought to evaluate the effectiveness of intermittent superficial cooling on thermoregulatory, cardiovascular, and perceptual responses during exercise in a hot humid environment. We used a randomized, counterbalanced, repeated measures investigation with 2 conditions (control and cooling) during exercise and recovery outdoors on artificial turf in a hot, humid tropical climate in the sun (wet bulb globe temperature outdoors [WBGTo], 27.0 ± 0.8° C; range, 25.8-28.1° C) and in the shade (WBGTo, 25.4 ± 0.9° C; range, 24.3-26.8° C). Participants were 10 healthy males (age, 22.6 ± 1.6 years; height, 176.0 ± 6.9 cm; mass, 76.5 ± 7.8 kg; body fat, 15.6 ± 5.4%) who wore shorts and T-shirt (control) or "phase change cooling" vest (cooling) during 5-minute rest breaks during 60 minutes of intense American football training and conditioning exercises in the heat and 30 minutes of recovery in the shade. Throughout, we measured core (Tgi) and skin (Tchest) temperature, heart rate (HR), thermal and thirst sensations, and rating of perceived exertion. We found significant (p ≤ 0.001) hypohydration (-2.1%); for Tgi, we found no significant differences between conditions (p = 0.674) during exercise and progressive decreases during recovery (p < 0.001). For [INCREMENT]Tg,i we found no significant (p = 0.090) differences. For Tchest, we found significantly (p < 0.001) decreased skin temperature in the cooling condition (Tchest, 31.85 ± 0.43° C) compared with the control condition (Tchest, 34.38 ± 0.43° C) during exercise and significantly (p < 0.001) lower skin temperature in the cooling condition (Tchest, 31.24 ± 0.47° C) compared with the control condition (Tchest, 33.48 ± 0.47° C) during recovery. For HR, we found no significant difference (p = 0.586) between the conditions during exercise; however, we did find significantly (p < 0.001) lower HR during recovery. Thermal sensations were significantly (p = 0.026) decreased in the cooling (4.4 ± 0.2 points) compared with the control (5.0 ± 0.2 points) condition but not for other perceptual responses. The cooling effects of "phase change cooling" material were effective in reducing skin temperature but did not sufficiently reduce core body temperature or cardiovascular strain.

The effect of ice ingestion on female athletes performing intermittent exercise in hot conditions

Studies have reported the benefits of pre-cooling prior to exercise in the heat for male athletes, but at this time no research has investigated female athletes. The aim of the following study was to test the effects of pre-cooling on female repeat sprint performance in hot, humid conditions; namely is ice ingestion effective in reducing core temperature (Tc) and does this reduced Tc lead to improved repeat sprint performance in female athletes? Nine female team sport athletes with mean age (21.0 ± 1.2 y), height (169.8 ± 4.1 cm) and body mass (62.3 ± 5.0 kg) participated in this study. Participants completed 72 min of an intermittent sprint protocol (ISP) consisting of 2 × 36 min halves in hot, humid conditions (33.1 ± 0.1 °C, 60.3 ± 1.5% RH) on a cycle ergometer. This was preceded by 30 min of either ice ingestion (ICE) or water consumption (CON) in a randomised order. At the end of the pre-cooling period, Tc significantly decreased following ICE (-0.7 ± 0.3 °C) compared to CON (-0.1 ± 0.2 °C; p = 0.001). Tc also remained lower in ICE compared to CON during the ISP (p = 0.001). Ratings of perceived thermal sensation were lower in ICE compared to CON (p = 0.032) at the beginning (p = 0.022) and mid-point (p = 0.035) of the second half. No differences in work, mean power, peak power, rating of perceived exertion, heart rate or sweat loss between conditions were recorded (p > 0.05). Ice ingestion significantly reduced female Tc prior to intermittent exercise in the heat and reduced thermal sensation; however, this did not coincide with improved performance.

Effect of a cooling vest on core temperature in athletes with and without spinal cord injury

BACKGROUND

It is well accepted that persons with spinal cord injury (SCI) have impaired ability to regulate core temperature due to impaired vasomotor and sudomotor activity below their level of injury. Impaired heat dissipation puts SCI athletes at great risk of exercise-induced hyperthermia (EIH) (>37.8°C). There is minimal evidence for efficacy of any specific cooling method in SCI athletes in a thermoneutral sport-specific setting.

OBJECTIVE

To evaluate the extent of EIH in persons with and without SCI and subsequently examine the effect of a cooling vest to attenuate rise in core body temperature (Tc).

METHODS

SCI (n = 17) and able-bodied (AB; n = 19) athletes participated in a 60-minute intermittent sprinting exercise in a thermoneutral (21.1°C-23.9°C) environment. Participants were separated according to their level of injury: tetraplegia defined as above T1 (TP; n = 6), high paraplegia defined as T5 through T1 (HP; n = 5), low paraplegia defined as T6 and below (LP; n = 6), and AB (n = 19). Tc was recorded at 15-minute intervals using an ingestible thermometer pill. This protocol was completed with a cooling vest (V) and without a cooling vest (NV).

RESULTS

All SCI and most AB athletes experienced EIH. After 60 minutes, Tc of TP athletes was significantly increased compared to HP (P = .03) and AB athletes (P = .007). There was no significant effect of the vest on Tc over time for any group.

CONCLUSIONS

TP athletes have the highest risk of exercise-induced hyperthermia. The cooling vest does not significantly attenuate rise in Tc in SCI or AB athletes.

Measuring intermittent exercise performance using shuttle running

The aim of this study was to include self-paced exercise within a modified Loughborough Intermittent Shuttle Test (LIST-P) in order to quantify key performance variables not possible with prescribed workloads. Sixteen male games players performed two trials of the LIST-P, at least 7 days apart. The LIST-P incorporates 4 × 15-min blocks of "prescribed-pace" activity (participants exercise in time to audible signals) followed by 2 × 15-min blocks of "self-paced" running (no audible signals). Distances covered and mean speeds were monitored during self-paced exercise. Total distance covered (12.54 ± 0.45 km vs. 12.64 ± 0.32 km; P = 0.10) and mean speed (8.37 ± 0.31 km ∙ h(-1) vs. 8.44 ± 0.22 km ∙ h(-1); P = 0.10) was similar between trials. Other indices also showed the test to be reliable (Pearson's correlation = 0.89 and 0.90 (P < 0.01), total distance and mean speed, respectively; intraclass correlation coefficient = 0.88 and 0.88 (P < 0.01); standard error of measurement = ±0.13 km and ±0.09 km ∙ h(-1); coefficient of variation (CV) = 1.7% and 1.7%; ratio limits of agreement = 1.00 */÷1.03 and 1.01 */÷1.04). Sprint time was also similar between trials (2.60 ± 0.19 s vs. 2.64 ± 0.23 s; P = 0.29). Incorporating self-paced exercise within an established intermittent shuttle running test appears to be a sensitive means of quantifying key performance variables for multiple-sprint sports research.

Effect of pre-cooling on repeat-sprint performance in seasonally acclimatised males during an outdoor simulated team-sport protocol in warm conditions

Whether precooling is beneficial for exercise performance in warm climates when heat acclimatised is unclear. The purpose of this study was to determine the effect of precooling on repeat-sprint performance during a simulated team-sport circuit performed outdoors in warm, dry field conditions in seasonally acclimatised males (n = 10). They performed two trials, one with precooling (PC; ice slushy and cooling jacket) and another without (CONT). Trials began with a 30-min baseline/cooling period followed by an 80 min repeat-sprint protocol, comprising 4 x 20-min quarters, with 2 x 5-min quarter breaks and a 10-min half-time recovery/cooling period. A clear and substantial (negative; PC slower) effect was recorded for first quarter circuit time. Clear and trivial effects were recorded for overall circuit time, third and fourth quarter sprint times and fourth quarter best sprint time, otherwise unclear and trivial effects were recorded for remaining performance variables. Core temperature was moderately lower (Cohen's d=0.67; 90% CL=-1.27, 0.23) in PC at the end of the precooling period and quarter 1. No differences were found for mean skin temperature, heart rate, thermal sensation, or rating of perceived exertion, however, moderate Cohen's d effect sizes suggested a greater sweat loss in PC compared with CONT. In conclusion, repeat- sprint performance was neither clearly nor substantially improved in seasonally acclimatised players by using a combination of internal and external cooling methods prior to and during exercise performed in the field in warm, dry conditions. Of practical importance, precooling appears unnecessary for repeat-sprint performance if athletes are seasonally acclimatised or artificially acclimated to heat, as it provides no additional benefit. Key PointsPre-cooling did not improve repeated sprint performance during a prolonged team-sport circuit in field conditions.If individuals are already heat acclimatised/acclimated, pre-cooling is unnecessary for performance enhancement.Acclimation/acclimatisation seems to be the more powerful method for protecting against heat strain.

The effect of cooling prior to and during exercise on exercise performance and capacity in the heat: a meta-analysis

Exercise is impaired in hot, compared with moderate, conditions. The development of hyperthermia is strongly linked to the impairment and as a result various strategies have been investigated to combat this condition. This meta-analysis focused on the most popular strategy: cooling. Precooling has received the most attention but recently cooling applied during the bout of exercise has been investigated and both were reviewed. We conducted a literature search and retrieved 28 articles which investigated the effect of cooling administered either prior to (n=23) or during (n=5) an exercise test in hot (wet bulb globe temperature >26°C) conditions. Mean and weighted effect size (Cohen's d) were calculated. Overall, precooling has a moderate (d=0.73) effect on subsequent performance but the magnitude of the effect is dependent on the nature of the test. Sprint performance is impaired (d=-0.26) but intermittent performance and prolonged exercise are both improved following cooling (d=0.47 and d=1.91, respectively). Cooling during exercise has a positive effect on performance and capacity (d=0.76). Improvements were observed in studies with and without cooling-induced physiological alterations, and the literature supports the suggestion of a dose-response relationship among cooling, thermal strain and improvements in performance and capacity. In summary, precooling can improve subsequent intermittent and prolonged exercise performance and capacity in a hot environment but sprint performance is impaired. Cooling during exercise also has a positive effect on exercise performance and capacity in a hot environment.

Precooling methods and their effects on athletic performance : a systematic review and practical applications

BACKGROUND

Precooling is a popular strategy used to combat the debilitating effects of heat-stress-induced fatigue and extend the period in which an individual can tolerate a heat-gaining environment. Interest in precooling prior to sporting activity has increased over the past three decades, with options including the application (external) and ingestion (internal) of cold modalities including air, water and/or ice, separately or in combination, immediately prior to exercise. Although many studies have observed improvements in exercise capacity or performance following precooling, some strategies are more logistically challenging than others, and thus are often impractical for use in competition or field settings.

OBJECTIVE

The purpose of this article was to comprehensively evaluate the established precooling literature, which addresses the application of cooling strategies that are likely to enhance field-based sports performance, while discussing the practical and logistical issues associated with these methods. We undertook a narrative examination that focused on the practical and event-specific application of precooling and its effect on physiological parameters and performance.

DATA SOURCES

Relevant precooling literature was located through the PubMed database with second- and third-order reference lists manually cross matched for relevant journal articles. The last day of the literature search was 31 January 2012.

STUDY SELECTION

Relevant studies were included on the basis of conforming to strict criteria, including the following: (i) cooling was conducted before exercise; (ii) cooling was conducted during the performance task in a manner that was potentially achievable during sports competition; (iii) a measure of athletic performance was assessed; (iv) subjects included were able bodied, and free of diseases or disorders that would affect thermoregulation; (v) subjects were endurance-trained humans (maximal oxygen uptake [[Formula: see text]O(2max)] >50 ml/kg/min for endurance protocols); (vi) cooling was not performed on already hyperthermic subjects that were in immediate danger of heat-related illnesses or had received passive heating treatments; (vii) drink ingestion protocols were used for the intended purpose of benefiting thermoregulation as a result of beverage temperature; and (viii) investigations employed ≥ six subjects. Initial searches yielded 161 studies, but 106 were discarded on failing to meet the established criteria. This final summary evaluated 74 precooling treatments, across 55 studies employing well trained subjects.

STUDY APPRAISAL AND SYNTHESIS METHODS

Key physiological and performance information from each study was extracted and presented, and includes respective subject characteristics, detailed precooling methods, exercise protocols, environmental conditions, along with physiological and performance outcomes. Data were presented in comparison to respective control treatments. For studies that include more than one treatment intervention, the comparative results between each precooling treatment were also presented. The practical benefits and limitations of employing each strategy in the field and in relation to sports performance were summarized.

RESULTS

Clear evidence of the benefits for a range of precooling strategies undertaken in the laboratory setting exists, which suggest that these strategies could be employed by athletes who compete in hot environmental conditions to improve exercise safety, reduce their perceived thermal stress and improve sports performance.

LIMITATIONS

This review did not include a systematic assessment of the study quality rating and provided a subjective assessment of the pooled outcomes of studies, which range in precooling methodologies and exercise outcomes. The wide range of research designs, precooling methods, environmental conditions and exercise protocols make it difficult to integrate all the available research into single findings.

CONCLUSION

Most laboratory studies have shown improvements in exercise performance following precooling and the emergence of strategies that are practically relevant to the field setting now allow scientists to individualize relevant strategies for teams and individuals at competition locations. Future research is warranted to investigate the effectiveness of practical precooling strategies in competition or field settings.

Superficial cooling does not decrease core body temperature before, during, or after exercise in an American football uniform

The purpose of this study was to identify the effects of superficial cooling on thermoregulatory responses while exercising in a hot humid environment while wearing an American football uniform. Nine male and female subjects wore a superficial cooling garment while in a cooling (CS) experimental condition or a no cooling (NCS) control condition during an exercise task consisting of warm-up (WU), exercise (EX), and recovery (R). The exercise task simulated an American football conditioning session with subjects wearing a full American football uniform and performing anaerobic and aerobic exercises in a hot humid environment. Subjects were allowed to drink water ad libitum during rest breaks. During the WU, EX, and R periods, core body temperature (T(c)) was measured to assess the effect of the cooling garment. Neither baseline resting before warm-up T(c) nor after warm-up T(c) was significantly different between trials. No significant differences in exercise T(c) between conditions were found. Time to return to baseline T(c) revealed no significant differences between the experimental and control conditions. The authors found that the volume of fluid consumed was 34% less in the experimental condition (711.1 ± 188.0 ml) compared with the control condition (1,077.8 ± 204.8 ml). The findings indicate that the cooling garment was not effective in blunting the rise in T(c) during warm-up, attenuating a rise in T(c) during intermittent exercise, or in increasing a return to baseline T(c) during a resting recovery period in a hot humid environment while wearing an American football uniform.

Repeated-sprint ability: where are we?

Repeated-sprint ability (RSA) is now well accepted as an important fitness component in team-sport performance. It is broadly described as the ability to perform repeated short (~3-4 s, 20-30 m) sprints with only brief (~10-30 s) recovery between bouts. Over the past 25 y a plethora of RSA tests have been trialed and reported in the literature. These range from a single set of ~6-10 short sprints, departing every 20-30 s, to team-sport game simulations involving repeating cycles of walk-jog-stride-sprint movements over 45-90 min. Such a wide range of RSA tests has not assisted the synthesis of research findings in this area, and questions remain regarding the optimal methods of training to best improve RSA. In addition, how RSA test scores relate to player "work rate," match performance, or both requires further investigation to improve the application of RSA testing and training to elite team-sport athletes.