Effects of Heat Acclimatization, Heat Acclimation, and Intermittent Exercise Heat Training on Time-Trial Performance

Squash in Los Angeles: Heat Strain and Performance Considerations at the 2028 Olympic Games

BACKGROUND

The Los Angeles 2028 Olympics will mark the debut of squash, a high-intensity sport characterized by repeated efforts, posing potential thermoregulatory challenges. The demanding nature of squash results in substantial metabolic heat production, with consequential heat strain exacerbated by the indoor environment of squash courts, where low to moderate evaporative potential limits effective cooling. Players often experience increased body-heat storage and thermal strain, with muscle cramps (an early warning sign of more severe heat-related illnesses) commonly observed during tournaments. Despite these challenges, there are limited data on the thermoregulatory responses of elite squash players during match play.

PURPOSE

We discuss the thermoregulatory challenges faced by squash players and highlight key areas for research. Additionally, practical guidelines are provided for practitioners preparing squash players for the Los Angeles 2028 Olympics.

EVIDENCE

Preliminary findings from international squash tournaments reveal that elite players endure significant physiological strain, with core temperatures rising to 39.0 °C to 40.1 °C, despite matches being played in mild wet-bulb globe temperatures of 19.4 °C (0.9 °C). Sustained heart rates exceeding 90% of maximal heart rate further compound this thermal strain. However, research on how thermal strain affects squash-specific fitness, recovery, and stroke mechanics are lacking. Such information is crucial for evaluating the need and effectiveness of tailored mitigation strategies such as heat training/exposures and precooling and midcooling during warm-up and match play.

CONCLUSION

Systematic research into the thermal demands of squash and their impact on fitness and skills is needed. These insights can inform evidence-based strategies to safeguard athlete well-being and optimize performance at Los Angeles 2028.

Radiofrequency and Electrical Muscle Stimulation: A Synergistic Treatment That Achieves Lipolysis and Circumferential Waist Reduction in Noninvasive Body Contouring

Background

Surgeons and providers in aesthetic medicine seek noninvasive devices that can be utilized for safe, efficient, and effective body contouring. Patient demand has propelled the development of novel devices that can simultaneously improve skin laxity, adipolysis along with stimulation of muscle hypertrophy.

Objectives

To determine the efficacy of body contouring after 3 treatments using the noninvasive Transform (InMode, Lake Forest, CA) device.

Methods

A prospective, multicenter study was performed. Outcomes evaluated include: standardized caliper and ultrasound measurements of abdominal skin/soft-tissue thickness, waist circumference, histologic evaluation, patient comfort, and satisfaction assessments.

Results

Forty-four patients were successfully enrolled in the study and completed the series of 3 treatments which involved combined electrical muscle stimulation (EMS) and noninvasive bipolar radiofrequency (RF). Abdominal ultrasound measurements reveal a decrease in soft-tissue thickness (average 3.1 mm; P = .001), there was a significant decrease in caliper measurements of periumbilical skin thickness (P < .003), and the average reduction of abdominal circumference was 1.9 cm (P < .0001) 3 months after the treatment series. Histology confirmed subcutaneous adipolysis without damaging the dermal layer. Patients reported a high degree of satisfaction with the overall result (P = .003) and that each of the 3 treatments were progressively more comfortable (P < .005).

Conclusions

This study demonstrates that a series of simultaneous noninvasive RF with EMS treatments to the abdomen decreases subcutaneous soft-tissue thickness of the treated area. These comfortable treatments ultimately result in a high degree of patient satisfaction at 3 months.

Level of Evidence 4

Effect of Heat Acclimatization, Heat Acclimation, and Intermittent Heat Training on Maximal Oxygen Uptake

BACKGROUND

Maximal oxygen uptake (VO2max) is an important determinant of endurance performance. Heat acclimation/acclimatization (HA/HAz) elicits improvements in endurance performance. Upon heat exposure reduction, intermittent heat training (IHT) may alleviate HA/HAz adaptation decay; however, corresponding VO2max responses are unknown.

HYPOTHESIS

VO2max is maintained after HAz/HA; IHT mitigates decrements in aerobic power after HAz/HA.

STUDY DESIGN

Interventional study.

LEVEL OF EVIDENCE

Level 3.

METHODS

A total of 27 male endurance runners (mean ± SD; age, 36 ± 12 years; body mass, 73.03 ± 8.97 kg; height, 178.81 ± 6.39 cm) completed VO2max testing at 5 timepoints; baseline, post-HAz, post-HA, and weeks 4 and 8 of IHT (IHT4, IHT8). After baseline testing, participants completed HAz, preceded by 5 days of HA involving exercise to induce hyperthermia for 60 minutes in the heat (ambient temperature, 39.13 ± 1.37°C; relative humidity, 51.08 ± 8.42%). Participants were assigned randomly to 1 of 3 IHT groups: once-weekly, twice-weekly, or no IHT. Differences in VO2max, velocity at VO2max (vVO2), and maximal heart rate (HRmax) at all 5 timepoints were analyzed using repeated-measure analyses of variance with Bonferroni corrections post hoc.

RESULTS

No significant VO2max or vVO2 differences were observed between baseline, post-HAz, or post-HA (P = 0.36 and P = 0.09, respectively). No significant group or time effects were identified for VO2max or vVO2 at post-HA, IHT4, and IHT8 (P = 0.67 and P = 0.21, respectively). Significant HRmax differences were observed between baseline and post-HA tests (P < 0.01). No significant group or time HRmax differences shown for post-HA, IHT4, and IHT8 (P = 0.59).

CONCLUSION

VO2max was not reduced among endurance runners after HA/HAz and IHT potentially due to participants' similar aerobic training status and high aerobic fitness levels.

CLINICAL RELEVANCE

HAz/HA and IHT maintain aerobic power in endurance runners, with HAz/HA procuring reductions in HRmax.

Environmental Stress Symptoms during Heat Acclimatization, Heat Acclimation, and Intermittent Heat Training

BACKGROUND

Athletes training in heat experience physiological and perceptual symptoms that risk their safety and performance without adaptation.

PURPOSE

We examined the changes in environmental symptoms, assessed with the Environmental Symptoms Questionnaire (ESQ), during heat acclimatization (HAz), heat acclimation (HA), and intermittent heat training (HT).

METHODS

Twenty-seven participants (mean ± standard deviation [M ± SD], age of 35 ± 12 y, VO2max of 57.7 ± 6.8 mL·kg-1·min-1) completed five trials involving 60 mins of running (60% vVO2max) followed by a 4 km time trial in heat (M ± SD, temperature of 35.5 ± 0.7 °C, humidity of 46.4 ± 1.5%). The trials occurred at baseline, post-HAz, post-HA, at week 4 of HT (post-HT4), and at week 8 of HT (post-HT8). The participants completed HT once/week (HTMIN), completed HT twice/week (HTMAX), or did not complete HT (HTCON). ESQ symptoms, thermal sensation (TS), and heart rate (HR) were measured pre- and post-trial.

RESULTS

Post-ESQ symptoms improved post-HA (3[0.40, 4.72], p = 0.02) and post-HAz (3[0.35, 5.05], p = 0.03) from baseline. During HT, symptoms improved in the HTMAX group and worsened in the HTMIN and HTCON groups. Symptoms improved in the HTMAX group versus the HTCON group at post-HT8 (4[1.02, 7.23], p = 0.012). Higher TS and HR values were weakly associated with ESQ symptoms during HT (r = 0.20, p = 0.04), only explaining 20% of variance.

CONCLUSIONS

ESQ symptoms improved during HAz, HA, and HT 2x/week. ESQ symptoms were not statistically correlated with HR during exercise heat stress. TS was not sensitive to detecting adaptation and did not subjectively change. The ESQ may be valuable in monitoring adaptation and may contribute to performance post-acclimation.

Using Predictive Modeling Technique to Assess Core Temperature Adaptations from Heart Rate, Sweat Rate, and Thermal Sensation in Heat Acclimatization and Heat Acclimation

Assessing the adaptation of rectal temperature (T_rec) is critical following heat acclimatization (HAz) and heat acclimation (HA) because it is associated with exercise performance and safety; however, more feasible and valid methods need to be identified. The purpose of this study was to predict adaptations in T_rec from heart rate (HR), sweat rate (SR), and thermal sensation (TS) using predictive modeling techniques. Twenty-five male endurance athletes (age, 36 ± 12 y; VO_2max, 57.5 ± 7.0 mL⋅kg^-1⋅min^-1) completed three trials consisting of 60 min running at 59.3 ± 1.7% vVO_2max in a hot environment. During trials, the highest HR and TS, SR, and T_rec at the end of trials were recorded. Following a baseline trial, participants performed HAz followed by a post-HAz trial and then completed five days HA, followed by a post-HA trial. A decision tree indicated cut-points of HR (<-13 bpm), SR (>0.3 L·h^-1), and TS (≤-0.5) to predict lower T_rec. When two or three variables met cut-points, the probability of accuracy of showing lower T_rec was 95.7%. Greater adaptations in T_rec were observed when two or three variables met cut-points (-0.71 ± 0.50 °C) compared to one (-0.13 ± 0.36 °C, p < 0.001) or zero (0.0 3 ± 0.38 °C, p < 0.001). Specificity was 0.96 when two or three variables met cut-points to predict lower T_rec. These results suggest using heart rate, sweat rate, and thermal sensation adaptations to indicate that the adaptations in T_rec is beneficial following heat adaptations, especially in field settings, as a practical and noninvasive method.

The Type of Per-Cooling Strategies Currently Employed by Competitive and Professional Cyclists-Triathletes During Training and Competition Are Condition (Dry vs. Humid) Dependant

Purpose

To investigate cooling strategies employed by athletes (cyclists-triathletes) during training and competition in hot and dry (HD) and hot and humid (HH) conditions.

Methods

Thirty-five athletes completed an online questionnaire on the type, timing, and justification of cooling strategies employed during past training and/or competitions in HD and HH conditions. In addition, 3 athletes also completed a one-to-one follow-up interview.

Results

Comparisons between strategies employed in all conditions were based on N = 14 (40%). Cold-water pouring was the most employed (N = 4; 21%) strategy during training and/or competing in hot conditions. The timing of the strategies employed was based on pitstops only (N = 7; 50%). The justification for strategies employed was based on trial and error (N = 9, 42.85%: N = 10, 47.61%). All athletes rated strategies employed as 1 (“not effective for minimising performance impairments and heat-related illnesses”). Comparisons between HD and HH were based on N = 21 (60%), who employed different strategies based on condition. Cold-water ingestion was the most employed (N = 9, 43%) strategy in HD, whereas a combination of cold-water ingestion and pouring was the most employed (N = 9, 43%) strategy in HH. The timing of strategies employed in the HD split was pre-planned by distance but was modified based on how athletes felt during (N = 8, 38%), and pre-planned by distance and pit stops (N = 8, 38%). The timing of strategies employed in HH was pre-planned based on distance and how athletes felt during (N = 9, 42%). About 57% (N = 12) of the 60% (N = 21) perceived effectiveness in HD and HH as 3 (“Sometimes effective and sometimes not effective”), whereas 43% (N = 9) of the 60% (N = 21) perceived effectiveness in HD and HH as 4 (“Effective for minimising performance impairments”).

Conclusion

Cold-water ingestion is the preferred strategy by athletes in HD compared to a combination of cold-water ingestion and pouring in HH conditions. All strategies were pre-planned and trialled based on distance and how athletes felt during training and/or competition. These strategies were perceived as effective for minimising performance impairments, but not heat-related illnesses. Future studies should evaluate the effectiveness of these cooling strategies on performance and thermoregulatory responses in HD and HH conditions.