Yoram Epstein

Purpose: To evaluate the association of elevated ambient heat stress with elite men's tennis performance, match dynamics and competitive outcomes. Methods: This retrospective cohort study analyzed 13,081 men’s matches in all four Grand Slam tournaments from 2000-2025, linked with localized meteorological data. Tournaments were classified as "Hot" if the mean Heat Index exceeded the local 26-year average by ≥1.0 standard deviation; remaining tournaments were classified as "Control". Categorical and continuous outcomes included measures of match completion, technical performance, competitive outcomes, and temporal match characteristics. Results: “Hot” tournaments clustered heavily in the last decade. Elevated thermal stress inverted the winner-minus-loser age gap from -0.21 to +0.16 years (p<0.01), indicating a relative advantage for older athletes. Match pace differed between environmental conditions: median match pace was 1.47 points per minute during Hot tournaments vs. 1.53 points per minute during Control tournaments (p<0.001), and median match duration was 149 min. vs. 141 min. (p<0.001). Technical metrics showed subtle alterations, including higher double-fault rates (3.71% vs. 3.50%, p<0.001). While overall match non-completion rates and ranking upsets remained stable globally, the non-completion rate nearly doubled at the US Open (8.35% vs. 4.65%, p<0.001). Conclusions: Elevated Heat Index was associated with small but consistent changes in elite men’s tennis match dynamics. The observed reduction in match pace is consistent with self-pacing under elevated thermal stress. These findings carry vital implications for sports sectors where the capacity to regulate effort intensity is constrained. Sporting organizations should consider proactive heat-management frameworks, including environmental monitoring, scheduling, acclimatization, and cooling interventions, to safeguard athletes' health and preserve performance.

Background: Screening blood tests are often collected from elite athletes in an effort to optimize performance. The purpose of the current study was to evaluate the yield of screening for anemia and anemia-related factors in elite athletes entering the Israeli Olympic team. Methods: We investigated hemoglobin levels, red blood cell count and indices and serum levels of iron, transferrin, ferritin, B12 and folic acid in 407 members of the Israeli Olympic team (179 females, 228 males) upon joining the team. Results: Forty-four (10.8%) athletes had abnormally lower Hb level (8.9% females and 12.3% males). Forty-two athletes (10.3%) had low RBC concentration (9.5% females and 11% males). Twenty-one athletes (5.2%) had low iron levels (7.9% in males and 1.7% in females) and only 14 athletes (7 males) had low ferritin levels (3.4%). Fourteen female athletes (7.8%) had ferritin levels of less than 20 ng/mL, and 43 (24%) had levels of less than 30 ng/mL. There were no cases of both anemia and low ferritin levels together. Twenty-five athletes (6.1%) had low levels of folic acid with higher prevalence (7%) in males. Only five athletes (1.2%) had low levels of vitamin B12, while 29 (7.1%) had levels higher than normal. None of them had abnormal Hb. In a multiple regression analysis, combat sports had significantly lower Hb levels. Conclusions: The yield of anemia screening and especially anemia-related biochemical abnormalities in adult elite athletes may be relatively low. Clearly, anemia should not be missed in the elite athlete, yet, if there are no signs or symptoms, Hb levels are close to normal and dilution is diagnosed, further frequent biochemical evaluation may be unnecessary.

Purpose: To evaluate the significance of body surface area-to-mass ratio (BSA/mass) on the heat-tolerance test (HTT) results. We hypothesized that individuals defined as heat tolerant (HT) would have on average higher BSA/mass compared with heat intolerant (HI) individuals. Methods: A retrospective reanalysis of the HTT results of 517 soldiers (age, 18–38 yr; M/F, 96%:4%), who were tested by the Israel Defense Forces HTT protocol. The criterion for heat tolerance in the current analysis was a rectal temperature (T_re) plateau during the second hour of the test. A logistic regression analysis to evaluate the predictive power of BSA/mass for heat intolerance was performed; the spline model was applied to show the odds for heat intolerance across BSA/mass. Results: In men BSA/mass of HI individuals was lower than HT individuals (248 ± 19 vs 262 ± 18 cm²·kg⁻¹, P < 0.01, d = 0.76). In women a similar trend was noted but with no statistical significance between HT and HI groups. The odd ratio for heat intolerance for every unit increase in BSA/mass was 0.97 (95% confidence interval, 0.95–0.99). The spline model plateaued above BSA/mass of 270 cm²·kg⁻¹. Conclusions: The results imply that body-core temperature responses to a standard exercise-heat stress (fixed external work rate and climatic conditions) are influenced by BSA/mass. More specifically, lack of a steady state in T_re (indicating heat intolerance) was more likely to occur with every unit decrease in BSA/mass. These findings contribute to a better understanding of the role of body anthropometry in the response to a standard exercise-heat task that might have an implication on clinical decision making about return to duty/play of soldiers, athletes, and others who deemed to be identified as HI.

Background: The prevalence of vitamin D deficiency has been a growing concern in recent years. Vitamin D is important in many of the body’s physiological systems, such as the musculoskeletal, cardiovascular and immune functions. A deficiency of vitamin D in athletes may negatively impact both muscle functions and recovery and, thus, affect performance and increase the risk of injury. Many studies assessed the prevalence of vitamin D deficiency in athletes; however, as of today, there are no official recommendations/protocols for screening vitamin D levels in athletes, and only a few studies were performed in male and female elite athletes (i.e., Olympic level), in different sport disciplines. Method: We investigated the prevalence of vitamin D deficiency among athletes entering the Israeli Olympic team. A total of 761 samples of Vitamin D(OH)25 from 334 athletes were analyzed. For this analysis, we used the first test the athlete had performed when joining the Olympic team. The prevalence of vitamin D deficiency (p < 0.0005). Conclusions: Due to the importance of vitamin D to athletic performance and the high prevalence of deficiency and insufficiency, we suggest careful and frequent monitoring of groups at risk, including elite athletes, especially in susceptible sports and during the winter. Future studies are necessary to investigate the effectiveness of Vitamin D supplementation in athletes with low baseline vitamin D levels.

Risk of exertional heat stroke (EHS) is an ongoing challenge for United States military personnel, for athletes and for individuals with occupational stressors that involve prolonged activity in hot environments. Higher body mass index (BMI) is significantly associated with increased risk for EHS in activity duty U.S. Soldiers. During exercise, heat is generated primarily by contracting skeletal muscle (and other metabolically active body mass) and dissipated based on body surface area (BSA). Thus, in compensable environments, a higher BSA·mass⁻¹ may be a benefit to heat dissipation and decrease the risk of EHS. The purpose of the present analysis was to test the hypothesis that BSA·mass⁻¹ ratio is an important biophysical characteristic contributing to the risk of EHS. We employed a matched case-control approach, where each individual with a diagnosis of EHS was matched to five controls who were never diagnosed with EHS but were in the same unit and had the same job title. We used a multivariate conditional logistic regression model including variables of BSA·mass⁻¹, sex, age, military rank, and race. BSA·mass⁻¹ significantly predicted EHS risk (P = 0.006), such that people with higher BSA·mass⁻¹ were at lower risk of developing EHS when controlling for other potential factors such as age and race. This relationship persisted after adjustment for other anthropometric measures of body size including weight, BMI, and BSA. These data suggest that biophysical factors play an important role in EHS risk, particularly in a healthy military-aged cohort of men and women. NEW & NOTEWORTHY With the impacts of climate change yielding higher average ambient temperatures over time, the incidence of EHS for individuals participating in outdoor activities may consequently increase. With the larger sample size in this study compared with prior research in this field, we were able to use various methods that had not been applied before. For example, we were able to mutually adjust for different measurements of body size to understand which metric had the highest association with EHS risk. Understanding factors that may be modifiable may be important for developing interventions to counteract the increased risk of EHS associated with climate change.

In a series of three companion papers published in this Journal, we identify and validate the available thermal stress indicators (TSIs). In this first paper of the series, we conducted a systematic review (registration: INPLASY202090088) to identify all TSIs and provide reliable information regarding their use (funded by EU Horizon 2020; HEAT-SHIELD). Eight databases (PubMed, Agricultural and Environmental Science Collection, Web of Science, Scopus, Embase, Russian Science Citation Index, MEDLINE, and Google Scholar) were searched from database inception to 15 April 2020. No restrictions on language or study design were applied. Of the 879 publications identified, 232 records were considered for further analysis. This search identified 340 instruments and indicators developed between 200 BC and 2019 AD. Of these, 153 are nomograms, instruments, and/or require detailed non-meteorological information, while 187 can be mathematically calculated utilizing only meteorological data. Of these meteorology-based TSIs, 127 were developed for people who are physically active, and 61 of those are eligible for use in occupational settings. Information regarding the equation, operating range, interpretation categories, required input data, as well as a free software to calculate all 187 meteorology-based TSIs is provided. The information presented in this systematic review should be adopted by those interested in performing on-site monitoring and/or big data analytics for climate services to ensure appropriate use of the meteorology-based TSIs. Studies two and three in this series of companion papers present guidance on the application and validation of these TSIs, to guide end users of these indicators for more effective use.

In a series of three companion papers published in this Journal, we identify and validate the available thermal stress indicators (TSIs). In this second paper of the series, we identified the criteria to consider when adopting a TSI to protect individuals who work in the heat, and we weighed their relative importance using a Delphi exercise with 20 experts. Two Delphi iterations were adequate to reach consensus within the expert panel (Cronbach’s α = 0.86) for a set of 17 criteria with varying weights that should be considered when adopting a TSI to protect individuals who work in the heat. These criteria considered physiological parameters such as core/skin/mean body temperature, heart rate, and hydration status, as well as practicality, cost effectiveness, and health guidance issues. The 17 criteria were distributed across three occupational health-and-safety pillars: (i) contribution to improving occupational health (55% of total importance), (ii) mitigation of worker physiological strain (35.5% of total importance), and (iii) cost-effectiveness (9.5% of total importance). Three criteria [(i) relationship of a TSI with core temperature, (ii) having categories indicating the level of heat stress experienced by workers, and (iii) using its heat stress categories to provide recommendations for occupational safety and health] were considered significantly more important when selecting a TSI for protecting individuals who work in the heat, accumulating 37.2 percentage points. These 17 criteria allow the validation and comparison of TSIs that presently exist as well as those that may be developed in the coming years.