A Mixed-Method Approach of Pre-Cooling Enhances High-Intensity Running Performance in the Heat

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.

Cumulative pre-cooling methods do not enhance cycling performance in tropical climate

The main objective of this study was to investigate the effect of mixed cooling techniques (combination of internal and external strategies, with and without menthol) during warm-up for a time trial in tropical climate. Seven heat-acclimatized trained male road cyclists participated in three experimental sessions consisting of 20-min cycling performances on a velodrome track in ecological hot and humid conditions (Guadeloupe, French West Indies; WBGT: 27.64±0.27°C; relative humidity: 76.43±2.19%), preceded by a standardized 30-min warm-up and the ingestion of cold menthol water (1) with a cooling vest soaked in ice water (ICE-VEST), (2) with a cooling vest soaked in ice menthol water (MEN-VEST), and (3) without a vest (NO-VEST). Cycling performance (total distance, distance traveled per 2-min block), physiological parameters (core body temperature recorded, heart rate) and perceptions (exertion, thermal comfort, thermal sensation) were assessed. No between-condition differences were found for physiological parameters, the total covered distance or the distance traveled per 2-min block. However, distance traveled per 2-min decreased with time (p = 0.03), with no difference between conditions, suggesting a variation in pace during the cycling performance trial (e.g., mean±SD: 1321±48.01m at T2; 1308±46.20m at T8, 1284±78.38m at T14, 1309±76.29m at T20). No between-condition differences were found for perception of exertion, thermal comfort and thermal sensation during the warm-up (11.83±3.34; 2.58±1.02; 4.39±0.94, respectively) and the performance (17.85±0.99; 2.70±1.25; 5.20±1.20, respectively) but the pairwise comparisons within condition revealed a significant increase of TS values from T0 (4.57±1.13) to T20 (6.00±0.58) only in NO-VEST condition (p = 0.04). The absence of modification of thermal sensation at the end of the cycling test under the mixed conditions (ICE-VEST and MEN-VEST) suggests a beneficial effect of wearing a cooling vest on thermal sensation although it had no effect on performance.

Effects of cutaneous administration of an over-the-counter menthol cream during temperate-water immersion for exercise-induced hyperthermia in men

Introduction: Hyperthermia impairs various physiological functions and physical performance. We examined the effects of cutaneous administration with an over-the-counter (OTC) analgesic cream containing 20% methyl salicylate and 6% L-menthol during temperate-water immersion (TWI) for exercise-induced hyperthermia. Methods: In a randomized crossover design, twelve healthy males participated in both of two experiments. Firstly, participants underwent a 15-min TWI at 20°C with (CREAM) or without (CON) cutaneous application of an analgesic cream. Cutaneous vascular conductance (CVC) was measured using laser doppler flowmetry during TWI. In a subsequent experiment, same participants performed a 30-min strenuous interval exercise in a heated (35°C) environment to induce hyperthermia (~39°C), which was followed by 15 min of TWI. Results: Core body temperature, as measured by an ingestible telemetry sensor, and mean arterial pressure (MAP) were measured. CVC and %CVC (% baseline) were higher during TWI in CREAM than in CON (Condition effect: p = 0.0053 and p = 0.0010). An additional experiment revealed that core body heat loss during TWI was greater in CREAM than in CON (Cooling rate: CON 0.070 ± 0.020 vs. CREAM 0.084°C ± 0.026°C/min, p = 0.0039). A more attenuated MAP response was observed during TWI in CREAM than in CON (Condition effect: p = 0.0007). Conclusion: An OTC analgesic cream containing L-menthol and MS augmented cooling effects when cutaneously applied during TWI in exercise-induced hyperthermia. This was, at least in part, due to the counteractive vasodilatory effect of the analgesic cream. The cutaneous application of OTC analgesic cream may therefore provide a safe, accessible, and affordable means of enhancing the cooling effects of TWI.

Effects of different external cooling placements prior to and during exercise on athletic performance in the heat: A systematic review and meta-analysis

Background: Nowadays, many high-profile international sport events are often held in warm or hot environments, hence, it is inevitable for these elite athletes to be prepared for the challenges from the heat. Owing to internal cooling may cause gastrointestinal discomfort to athletes, external cooling technique seems to be a more applicable method to deal with thermal stress. Central cooling mainly refers to head, face, neck and torso cooling, can help to reduce skin temperature and relieve thermal perception. Peripheral cooling mainly refers to four limbs cooling, can help to mitigate metabolic heat from muscular contrac to effectively prevent the accumulation of body heat. Hence, we performed a meta-analysis to assess the effectiveness of different external cooling placements on athletic performance in the heat Methods: A literatures search was conducted using Web of Science, MEDLINE and SPORTDiscus until September 2022. The quality and risk of bias in the studies were independently assessed by two researchers. Results: 1,430 articles were initially identified (Web of Science = 775; MEDLINE = 358; SPORTDiscus = 271; Additional records identified through other sources = 26), 60 articles (82 experiments) met the inclusion criteria and were included in the final analysis, with overall article quality being deemed moderate. Central cooling (SMD = 0.43, 95% CI 0.27 to 0.58, p < 0.001) was most effective in improving athletic performance in the heat, followed by central and peripheral cooling (SMD = 0.38, 95% CI 0.23 to 0.54, p < 0.001), AND peripheral cooling (SMD = 0.32, 95% CI 0.07 to 0.57, p = 0.013). For the cooling-promotion effects on different sports types, the ranking order in central cooling was ETE (exercise to exhaustion), TT (time-trial), EWT (exercise within the fixed time or sets), IS (intermittent sprint); the ranking order in peripheral cooling was EWT, TT, ETE and IS; the ranking order in central and peripheral cooling was ETE, IS, EWT and TT. Conclusion: Central cooling appears to be an more effective intervention to enhance performance in hot conditions through improvements of skin temperature and thermal sensation, compared to other external cooling strategies. The enhancement effects of peripheral cooling require sufficient re-warming, otherwise it will be trivial. Although, central and peripheral cooling seems to retain advantages from central cooling, as many factors may influence the effects of peripheral cooling to offset the positive effects from central cooling, the question about whether central and peripheral cooling method is better than an isolated cooling technique is still uncertain and needs more researchs to explore it.

Effects of mixed-cooling strategies on executive functions in simulated tennis in hot and humid conditions

This study aimed to investigate the effects of mixed-cooling strategies, which combines external (cooling vest + neck cooled collar) and internal cooling (cold sports drink ingestion) on measures of executive function during simulated tennis in hot/humid conditions. In a counterbalanced design (randomised order), eight males undertook two trials [one with the mixed-cooling strategy, (MCOOL condition) and another without (CON condition)] in a climate chamber (36.5°C, 50% relative humidity). All subjects completed an intermittent treadmill protocol simulating a three-set tennis match with a 90-second break during odd-numbered games and 120-second breaks between sets, in accordance with the activity profile and International Tennis Federation rules. The mixed-cooling strategies were adopted before test and break time during the simulated tennis match. Stroop task, 2-back task, More-odd shifting task, gastrointestinal temperature (Tgi), skin temperature, blood lactic acid (BLA), heart rate, urine specific gravity (USG), sweat rate (SR), thermal sensation (TS) and perceived exertion (RPE) were measured. Results showed that the mean exercise time was longer in the MCOOL condition than in the CON condition. The SR was greater in CON trial compared with that in MCOOL trial. Results of two-way analysis of variance with repeated measures revealed that time×condition interactions were significant in BLA, Stroop response time, and switch cost of the more-odd shifting task. There were main effects of condition for Tgi, HR, TS, RPE, BLA, Stroop response time, and switch cost of the more-odd shifting task. In a hot/wet environment, pre- and intermittent mixed-cooling strategies can significantly improve exercise time and measures of executive function of tennis players in a simulated tennis match.

Performance effects of internal pre- and per-cooling across different exercise and environmental conditions: A systematic review

Exercise in a hot and humid environment may endanger athlete's health and affect physical performance. This systematic review aimed to examine whether internal administration of ice, cold beverages or menthol solutions may be beneficial for physical performance when exercising in different environmental conditions and sports backgrounds. A systematic search was performed in PubMed, Web of Science, Scopus and SPORTDiscus databases, from inception to April 2022, to identify studies meeting the following inclusion criteria: healthy male and female physically active individuals or athletes (aged ≥18 years); an intervention consisting in the internal administration (i.e., ingestion or mouth rinse) of ice slush, ice slurry or crushed ice and/or cold beverages and/or menthol solutions before and/or during exercise; a randomized crossover design with a control or placebo condition; the report of at least one physical performance outcome; and to be written in English. Our search retrieved 2,714 articles in total; after selection, 43 studies were considered, including 472 participants, 408 men and 64 women, aged 18-42 years, with a VO2max ranging from 46.2 to 67.2 mL⋅kg-1⋅min-1. Average ambient temperature and relative humidity during the exercise tasks were 32.4 ± 3.5°C (ranging from 22°C to 38°C) and 50.8 ± 13.4% (varying from 20.0% to 80.0%), respectively. Across the 43 studies, 7 exclusively included a menthol solution mouth rinse, 30 exclusively involved ice slurry/ice slush/crushed ice/cold beverages intake, and 6 examined both the effect of thermal and non-thermal internal techniques in the same protocol. Rinsing a menthol solution (0.01%) improved physical performance during continuous endurance exercise in the heat. Conversely, the ingestion of ice or cold beverages did not seem to consistently increase performance, being more likely to improve performance in continuous endurance trials, especially when consumed during exercises. Co-administration of menthol with or within ice beverages seems to exert a synergistic effect by improving physical performance. Even in environmental conditions that are not extreme, internal cooling strategies may have an ergogenic effect. Further studies exploring both intermittent and outdoor exercise protocols, involving elite male and female athletes and performed under not extreme environmental conditions are warranted. Systematic review registration: [https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021268197], identifier [CRD42021268197].

Modulation of Leukocyte Subsets Mobilization in Response to Exercise by Water Immersion Recovery

Purpose: To investigate the effect of different water immersion temperatures on the kinetics of blood markers of skeletal muscle damage and the main leukocyte subpopulations. Methods: Eleven recreationally trained young men participated in four experimental sessions consisting of unilateral eccentric knee flexion and 90 min of treadmill running at 70% of peak oxygen uptake, followed by 15 min of water immersion recovery at 15, 28 or 38°C. In the control condition participants remained seated at room temperature. Four hours after exercise recovery, participants completed a performance test. Blood samples were obtained before and immediately after exercise, after immersion, immediately before and after the performance test and 24 h after exercise. The number of leukocyte populations and the percentage of lymphocyte and monocytes subsets, as well as the serum activity of creatine kinase and aspartate aminotransferase were determined. Results: Leukocytosis and increase in blood markers of skeletal muscle damage were observed after the exercise. Magnitude effect analysis indicated that post-exercise hot-water immersion likely reduced the exercise-induced lymphocytosis and monocytosis. Despite reduced monocyte count, recovery by 38°C immersion, as well as 28°C, likely increased the percentage of non-classical monocytes in the blood. The percentage of CD25⁺ cells in the CD4 T cell subpopulation was possibly lower after immersion in water at 28 and 15°C. No effect of recovery by water immersion was observed for serum levels of creatine kinase and aspartate aminotransferase. Conclusions: Recovery by hot-water immersion likely attenuated the leukocytosis and increased the mobilization of non-classical monocytes induced by a single session of exercise combining resistance and endurance exercises, despite no effect of water immersion on markers of skeletal muscle damage. The monocyte response mediated by hot water immersion may lead to the improvement of the inflammatory response evoked by exercise in the skeletal muscle.

Topical Analgesic Containing Methyl Salicylate and L-Menthol Accelerates Heat Loss During Skin Cooling for Exercise-Induced Hyperthermia

Hyperthermia impairs physical performance and, when prolonged, results in heat stroke or other illnesses. While extensive research has investigated the effectiveness of various cooling strategies, including cold water immersion and ice-suit, there has been little work focused on overcoming the cutaneous vasoconstriction response to external cold stimulation, which can reduce the effectiveness of these treatments. Over-the-counter (OTC) topical analgesics have been utilized for the treatment of muscle pain for decades; however, to date no research has examined the possibility of taking advantage of their vasodilatory functions in the context of skin cooling. We tested whether an OTC analgesic cream containing 20% methyl salicylate and 6% L-menthol, known cutaneous vasodilators, applied to the skin during skin cooling accelerates heat loss in exercise-induced hyperthermia. Firstly, we found that cutaneous application of OTC topical analgesic cream can attenuate cold-induced vasoconstriction and enhance heat loss during local skin cooling. We also revealed that core body heat loss, as measured by an ingestible telemetry sensor, could be accelerated by cutaneous application of analgesic cream during ice-suit cooling in exercise-induced hyperthermia. A blunted blood pressure response was observed during cooling with the analgesic cream application. Given the safety profile and affordability of topical cutaneous analgesics containing vasodilatory agents, our results suggest that they can be an effective and practical tool for enhancing the cooling effects of skin cooling for hyperthermia.