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.

Exertional Heatstroke Survivors' Knowledge and Beliefs about Exertional Heatstroke Diagnosis, Treatment, and Return to Play.

CONTEXT: Little information exists regarding what exertional heatstroke (EHS) survivors know and believe about EHS best practices. Understanding this would help clinicians focus educational efforts to ensure survival and safe return-to-play following EHS. OBJECTIVE: We sought to better understand what EHS survivors knew about EHS seriousness (e.g., lethality, short- and long-term effects), diagnosis and treatment procedures, and recovery. Design: Multi-year, cross-sectional, descriptive design. SETTING: An 11.3-km road race located in the Northeastern United States in August 2022 and 2023. PATIENTS OR OTHER PARTICIPANTS: Forty-two of 62 runners with EHS (15 women, 27 men; age: 33±15 y; pre-treatment rectal temperature [TREC]: 41.5±0.9°C). INTERVENTIONS: Medical professionals evaluated runners requiring medical attention at the finish line. If they observed TREC ≥40°C with concomitant central nervous system dysfunction (CNS) EHS was diagnosed and patients were immersed in a 189.3-L tub filled with ice-water. Before medical discharge, we asked EHS survivors 15 questions about their experience and knowledge of select EHS best practices. Survey items were piloted and validated by experts and laypersons a priori (content validity index ≥0.88 for items and scale). MAIN OUTCOME MEASURES: Survey responses. RESULTS: Sixty-seven percent (28/42) of patients identified EHS as potentially fatal and 76% (32/42) indicated it negatively affected health. Seventy-nine percent (33/42) correctly identified TREC as the best temperature site to diagnose EHS. Most patients (74%, 31/42) anticipated returning to normal exercise within 1 week post-EHS; 69% (29/42) stated EHS would not impact future race participation. Patients (69%, 29/42) indicated it was important to tell their primary care physician about their EHS. CONCLUSIONS: Our patients were knowledgeable on the potential seriousness and adverse health effects of EHS and the necessity of TREC for diagnosis. However, educational efforts should be directed towards helping patients understand safe recovery and return-to-play timelines following EHS.

Recommended water immersion duration for the field treatment of exertional heat stroke when rectal temperature is unavailable.

INTRODUCTION: The recommended treatment for exertional heat stroke is immediate, whole-body immersion in < 10 °C water until rectal temperature (Tre) reaches ≤ 38.6 °C. However, real-time Tre assessment is not always feasible or available in field settings or emergency situations. We defined and validated immersion durations for water temperatures of 2-26 °C for treating exertional heat stroke. METHODS: We compiled data for 54 men and 18 women from 7 previous laboratory studies and derived immersion durations for reaching 38.6 °C Tre. The resulting immersion durations were validated against the durations of cold-water immersion used to treat 162 (98 men; 64 women) exertional heat stroke cases at the Falmouth Road Race between 1984 and 2011. RESULTS: Age, height, weight, body surface area, body fat, fat mass, lean body mass, and peak oxygen uptake were weakly associated with the cooling time to a safe Tre of 38.6 °C during immersions to 2-26 °C water (R2 range: 0.00-0.16). Using a specificity criterion of 0.9, receiver operating characteristics curve analysis showed that exertional heat stroke patients must be immersed for 11-12 min when water temperature is ≤ 9 °C, and for 18-19 min when water temperature is 10-26 °C (Cohen's Kappa: 0.32-0.75, p < 0.001; diagnostic odds ratio: 8.63-103.27). CONCLUSION: The reported immersion durations are effective for > 90% of exertional heat stroke patients with pre-immersion Tre of 39.5-42.8 °C. When available, real-time Tre monitoring is the standard of care to accurately diagnose and treat exertional heat stroke, avoiding adverse health outcomes associated with under- or over-cooling, and for implementing cool-first transport second exertional heat stroke policies.

Exertional Heat Stroke Survival at the Falmouth Road Race: 180 New Cases With Expanded Analysis.

CONTEXT: A high number of exertional heat stroke (EHS) cases occur during the Falmouth Road Race. OBJECTIVES: To extend previous analyses of EHS cases during the Falmouth Road Race by assessing or describing (1) EHS and heat exhaustion (HE) incidence rates, (2) EHS outcomes as they relate to survival, (3) the effect of the environment on these outcomes, and (4) how this influences medical provider planning and preparedness. DESIGN: Descriptive epidemiologic study. SETTING: Falmouth Road Race. PATIENTS OR OTHER PARTICIPANTS: Patients with EHS or HE admitted to the medical tent. MAIN OUTCOME MEASURE(S): We obtained 8 years (2012 to 2019) of Falmouth Road Race anonymous EHS and HE medical records. Meteorologic data were collected and analyzed to evaluate the effect of environmental conditions on the heat illness incidence (exertional heat illness [EHI] = EHS + HE). The EHS treatment and outcomes (ie, cooling time, survival, and discharge outcome), number of HE patients, and wet bulb globe temperature (WBGT) for each race were analyzed. RESULTS: A total of 180 EHS and 239 HE cases were identified. Overall incidence rates per 1000 participants were 2.07 for EHS and 2.76 for HE. The EHI incidence rate was 4.83 per 1000 participants. Of the 180 EHS cases, 100% survived, and 20% were transported to the emergency department. The WBGT was strongly correlated with the incidence of both EHS (r2 = 0.904, P = .026) and EHI (r2 = 0.912, P = .023). CONCLUSIONS: This is the second-largest civilian database of EHS cases reported. When combined with the previous dataset of EHS survivors from this race, it amounts to 454 EHS cases resulting in 100% survival. The WBGT remained a strong predictor of EHS and EHI cases. These findings support 100% survival from EHS when patients over a wide range of ages and sexes are treated with cold-water immersion.

Analysis of Exertion-Related Injuries and Fatalities in Laborers in the United States.

Laborers are particularly vulnerable to exertional injuries and illnesses, as they often engage in heavy physical work for prolonged hours, yet no studies have examined the top causes of catastrophic exertional injuries and fatalities among this population. The purpose of the investigation was to characterize the top causes of exertional injury and fatality within open access, Occupational Safety and Health Administration (OSHA) reportable data. A secondary analysis of OSHA reported injury and fatality data was performed through open access records from OSHA Severe Injury Reports (2015-2022) and OSHA fatality inspection data (2017-2020), respectively. The research team characterized each reported injury and fatality as "exertion-related" or "non-exertion-related. Injury and fatality rates were reported per 100,000 equivalent full-time worker years and included 95% confidence intervals (95% CI). Of 58,648 cases in the OSHA Severe Injury Report database from 2015-2020, 1682 cases (2.9%) were characterized as exertional (0.20 injuries per 100,000 full-time worker years, 95% CI: 0.19, 0.22). Heat-related injuries encompassed 91.9% of the exertional injuries (n = 1546). From the 2017-2022 OSHA fatality inspection database, 89 (1.9%) of 4598 fatalities were characterized as exertion-related (fatality rate: 0.0160 per 100,000 full-time equivalent workers, 95% CI: 0.009, 0.0134). The exertion-related fatalities primarily consisted of heat-related cases (87.6%). Exertion-related injuries and fatalities were most reported in Southeast states, in the construction and excavation industry, and among nonunionized workers. As heat stress continues to be recognized as an occupational health and safety hazard, this analysis further highlights the need for targeted interventions or further evaluation of the impact of heat stress on construction and excavation workers, nonunionized workers, and workers in Southeastern states.

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.

Youth Athletes' Parents' Perceptions and Knowledge of the Athletic Training Profession.

CONTEXT: Parents have unique roles in advocating for their child's health and safety. Such advocacy can improve student-athletes' access to athletic trainers (ATs), yet few researchers have investigated the perceptions of student-athletes' parents regarding athletic training. OBJECTIVE: To explore parents' perceptions of athletic training and evaluate their knowledge regarding the AT's role. DESIGN: Concurrent mixed-methods study. SETTING: Web-based questionnaire. PATIENTS OR OTHER PARTICIPANTS: Parents affiliated with USA Football representing 36 states (n = 316: men = 53.5%, women = 46.1%; average age = 45.6 ± 6.2 years [age provided = 291]) were included. MAIN OUTCOME MEASURE(S): An online questionnaire was developed and distributed via Qualtrics. The questionnaire contained demographic questions, quantitative items assessing perceived value and knowledge of athletic training, and open-ended questions to provide opportunities for expansion. Descriptive statistics were calculated for the demographic data. Quantitative measures were presented as count and percentage responses. Open-ended responses were analyzed using the general inductive approach, and overall perceptions were supported with participant quotes. RESULTS: Of 10 763 parents, 390 completed the questionnaire (3.6% response rate, 74.8% completion rate). Of the 390, 316 had a child in high school. Approximately 67% (n = 213) of respondents considered an AT a trusted source of medical information and "extremely valuable" to student-athletes' health and safety. The questionnaire response injury prevention was frequently recognized (n = 307, 97.2%) as a skill ATs perform, followed by first aid/wound care (91.8%) and therapeutic interventions (82.3%). Parents highlighted the AT's role in immediate care and attributed peace of mind and feelings of comfort to having a health care professional readily available for their children. CONCLUSIONS: When asked directly and when discussing their effect on student-athlete health and safety, parents valued ATs. Though various qualifications of ATs were recognized, parents emphasized the importance of having someone immediately available to provide care if and when needed. Educational efforts should focus on ATs as the most qualified health care professionals to provide comprehensive medical care to student-athletes in both urgent and nonurgent situations.

Secondary School Athletic Coaches' Perceptions and Knowledge of the Athletic Training Profession.

CONTEXT: Coaches play a role in streamlining care, especially by directing student-athletes in need of further medical attention to the athletic trainer (AT). The AT-coach relationship holds great potential for incorporating collaborative care, and yet, little is known about coaches' perceptions and knowledge of ATs. OBJECTIVE: To investigate coaches' perceptions of athletic training and their knowledge regarding the roles and responsibilities of ATs in secondary schools. DESIGN: Concurrent mixed-methods study. SETTING: Cross-sectional online questionnaire. PATIENTS OR OTHER PARTICIPANTS: Secondary school athletic coaches from 10 sports with the highest participation rates during the 2017-2018 season (n = 1097). Most respondents were male (n = 795, 72.4%), and their average age was 44.7 ± 11.4 years. MAIN OUTCOME MEASURE(S): Participants completed a web-based questionnaire containing demographics and quantitative measures assessing their perceived value and knowledge of ATs, as well as open-ended questions. Descriptive statistics summarized the demographic data. Counts and percentage responses for quantitative measures were reported. Open-ended responses were analyzed using the general inductive approach. RESULTS: Approximately 93% of respondents considered an AT a trusted source of medical information and a key member of the sports medicine team. Most respondents selected injury prevention (98.9%), first aid and wound care (97%), therapeutic interventions (89.9%), and emergency care (85.8%) as skills ATs are qualified to perform. Forty-six percent of respondents were willing to coach without an AT employed. Coaches trusted ATs as part of the "athletic team" and as gatekeepers, referring student-athletes for advanced care when warranted. Regarding the AT role, coaches emphasized the treatment of minor injuries and the idea of "coverage versus care." CONCLUSIONS: Secondary school coaches valued the athletic training profession and were knowledgeable regarding various roles and responsibilities ATs frequently perform. However, they may view ATs as luxuries instead of necessities, as evidenced by the fact that just under half of responding coaches were willing to coach without an AT employed at the school.

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 (Trec) 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 Trec from heart rate (HR), sweat rate (SR), and thermal sensation (TS) using predictive modeling techniques. Twenty-five male endurance athletes (age, 36 ± 12 y; VO2max, 57.5 ± 7.0 mL⋅kg-1⋅min-1) completed three trials consisting of 60 min running at 59.3 ± 1.7% vVO2max in a hot environment. During trials, the highest HR and TS, SR, and Trec 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 Trec. When two or three variables met cut-points, the probability of accuracy of showing lower Trec was 95.7%. Greater adaptations in Trec 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 Trec. These results suggest using heart rate, sweat rate, and thermal sensation adaptations to indicate that the adaptations in Trec is beneficial following heat adaptations, especially in field settings, as a practical and noninvasive method.

Effects of Heat Acclimation Following Heat Acclimatization on Whole Body Heat Exchange in Trained Endurance Athletes.

The purpose of this study was to examine the changes in metabolic heat production (Hprod), evaporative heat loss (Hevap), and dry heat loss (Hdry), following heat acclimatization (HAz) and heat acclimation (HA). Twenty-two male endurance athletes (mean ± standard deviation; age, 37 ± 12 y; body mass, 73.4 ± 8.7 kg; height, 178.7 ± 6.8 cm; and VO2max, 57.1 ± 7.2 mL·kg−1·min−1) completed three trials (baseline; post-HAz; and post-HA), which consisted of 60 min steady state exercise at 59 ± 2% velocityVO2max in the heat (ambient temperature [Tamb], 35.2 ± 0.6 °C; relative humidity [%rh] 47.5 ± 0.4%). During the trial, VO2 and RER were collected to calculate Hprod, Hevap, and Hdry. Following the baseline trial, participants completed self-directed outdoor summer training followed by a post-HAz trial. Then, five days of HA were completed over eight days in the heat (Tamb, 38.7 ± 1.1 °C; %rh, 51.2 ± 2.3%). During the HA sessions, participants exercised to maintain hyperthermia (38.50 °C and 39.75 °C) for 60 min. Then, a post-HA trial was performed. There were no differences in Hprod between the baseline (459 ± 59 W·m−2), post-HAz (460 ± 61 W·m−2), and post-HA (464 ± 55 W·m−2, p = 0.866). However, Hevap was significantly increased post-HA (385 ± 84 W·m−2) compared to post-HAz (342 ± 86 W·m−2, p = 0.043) and the baseline (332 ± 77 W·m−2, p = 0.037). Additionally, Hdry was significantly lower at post-HAz (125 ± 8 W·m−2, p = 0.013) and post-HA (121 ± 10 W·m−2, p < 0.001) compared to the baseline (128 ± 7 W·m−2). Hdry at post-HA was also lower than post-HAz (p = 0.049). Hprod did not change following HAz and HA. While Hdry was decreased following HA, the decrease in Hdry was smaller than the increases in Hevap. Adaptations in body heat exchange can occur by HA following HAz.

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

BACKGROUND: The purpose of this study was to investigate effects of heat acclimatization (HAz) followed by heat acclimation (HA), and intermittent heat training (IHT) on time-trial performance. HYPOTHESIS: Time-trial performance will improve after HA and will further improve with twice a week of IHT. STUDY DESIGN: Interventional study. LEVEL OF EVIDENCE: Level 3. METHODS: A total of 26 male athletes (mean ± SD; age, 35 ± 12 years; body mass, 72.8 ± 8.9 kg; peak oxygen consumption [VO2peak], 57.3 ± 6.7 mL·kg-1·min-1) completed five 4-km time trials (baseline, post-HAz, post-HA, post-IHT4, post-IHT8) in the heat (ambient temperature, 35.4°C ± 0.3°C; relative humidity, 46.7% ± 1.2%) on a motorized treadmill. After baseline time trial, participants performed HAz (109 ± 10 days) followed by post-HAz time trial. Then, participants completed 5 days of HA, which involved exercising to induce hyperthermia (38.50°C-39.75°C) for 60 minutes. Participants were then divided into 3 groups and completed IHT either twice per week (IHTMAX), once per week (IHTMIN), or not at all (IHTCON) over an 8-week period. The exercise used for the IHT matched the HA. Four-kilometer time trials were performed after 4 weeks (post-IHT4) and 8 weeks of IHT (post-IHT8). RESULTS: Time trial was faster in post-HA (17.98 ± 2.51 minutes) compared with baseline (18.61 ± 3.06 minutes; P = 0.037) and post-HAz (18.66 ± 3.12 minutes; P = 0.023). Percentage change in time trial was faster in IHTMAX (-3.9% ± 5.2%) compared with IHTCON (11.5% ± 16.9%) (P = 0.020) and approached statistical significance with large effect (effect size = 0.96) compared with IHTMIN (1.6% ± 6.2%; P = 0.059) at post-IHT8. Additionally, IHTMAX (-2.2% ± 4.2%) was faster than IHTCON (3.6% ± 6.9%) (P = 0.05) at post-IHT4. CONCLUSION: These results indicate that HA after HAz induces additional improvement in time-trial performance. IHT twice per week shows improvement after 8 weeks, while once per week maintains performance for 8 weeks. No IHT results in a loss of adaptations after 4 weeks and even greater losses after 8 weeks. CLINICAL RELEVANCE: HA after HAz improves time-trial performance, twice a week of IHT improves performance further, and once a week of IHT maintains performance for at least 8 weeks.

Relationships Between WUT (Body Weight, Urine Color, and Thirst Level) Criteria and Urine Indices of Hydration Status.

BACKGROUND: A Venn diagram consisting of percentage body mass loss, urine color, and thirst perception (weight, urine, thirst [WUT]) has been suggested as a practical method to assess hydration status. However, no study to date has examined relationships between WUT and urine hydration indices. Thus, the purpose of this study was to investigate relationships between urine specific gravity, urine osmolality, and the WUT criteria. HYPOTHESIS: Urine specific gravity and urine osmolality indicate hypohydration when the WUT criteria demonstrate hypohydration (≥2 markers). STUDY DESIGN: Laboratory cohort study. LEVEL OF EVIDENCE: Level 3. METHODS: A total of 22 women (mean ± SD; age, 20 ± 1 years; mass, 65.4 ± 12.6 kg) and 21 men (age, 21 ± 1 years; body mass, 78.7 ± 14.6 kg) participated in this study. First morning body mass, urine color, urine specific gravity, urine osmolality, and thirst level were collected for 10 consecutive days in a free-living situation. Body mass loss >1%, urine color >5, and thirst level ≥5 were used as the dehydration thresholds. The number of markers that indicated dehydration levels were counted and categorized into either 3, 2, 1, or 0 WUT markers that indicated dehydration. One-way analysis of variance with Tukey pairwise comparisons was used to assess the differences in urine specific gravity and urine osmolality between the different number of WUT markers. RESULTS: Urine specific gravity in 3 WUT markers (mean ± SD [effect size], 1.021 ± 0.007 [0.57]; P = 0.025) and 2 WUT markers (1.019 ± 0.010 [0.31]; P = 0.026) was significantly higher than 1 WUT marker (1.016 ± 0.009). Urine mosmolality in 2 WUT markers (705 ± 253 mOsmol [0.43]; P = 0.018) was significantly higher than 1 WUT (597 ± 253 mOsmol). Meeting at 3 WUT resulted in specificity of 0.956 and at 0 WUT resulted in sensitivity of 0.937 for urine osmolality>700mOsm. CONCLUSION: These results suggest that when 3 WUT markers are met, urine specific gravity and urine osmolality indicated hypohydration and 0 WUT represents a high likelihood of euhydration. 1 and 2 WUT values are indeterminate of hydration status. The WUT criterion is a useful tool to use in field settings to assess hydration status when first morning urine sample was used. CLINICAL RELEVANCE: Athletes, coaches, sports scientists, and medical professionals can use WUT criteria to monitor dehydration with reduced cost and time.

The efficacy of weekly and bi-weekly heat training to maintain the physiological benefits of heat acclimation.

OBJECTIVES: To examine the efficacy of weekly and bi-weekly heat training to maintain heat acclimatization (HAz) and heat acclimation (HA) for 8 weeks in aerobically trained athletes. DESIGN: Randomized, between-group. METHODS: Twenty-four males (mean [m ±â€¯standard deviation [sd]; (age, 34 ±â€¯12 y; body mass, 72.6 ±â€¯8.8 kg, VO2peak, 57.7 ±â€¯6.8 mL·kg-1·min-1) completed five trials (baseline, following HAz, following HA (HAz + HA), four weeks into heat training [HTWK4], and eight weeks into HT [HTWK8] that involved 60 min of steady-state exercise (59.1 ±â€¯1.8% vVO2peak) in an environmental laboratory (wet bulb globe temperature [WBGT], 29.6 ±â€¯1.4 °C) on a motorized treadmill. Throughout exercise, heart rate (HR) and rectal temperature (Trec) were recorded. Following HAz + HA, participants were assigned to three groups: control group (HT0), once per week heat training (HT1), and twice per week heat training (HT2). HT involved heated exercise (WBGT, 33.3 ±â€¯1.3 °C) to achieve hyperthermia (38.5-39.75 °C) for 60 min. Repeated measures ANOVAs were used to determine differences. RESULTS: HAz + HA resulted in significant improvements in HR (p < 0.001) and Trec (p < 0.001). At HTWK8, HR was significantly higher in HT0 (174 ±â€¯22 beats⋅min-1) compared to HT2 (151 ±â€¯17 beats⋅min-1, p < 0.023), but was not different than HT1 (159 ±â€¯17 beats⋅min-1, p = 0.112). There was no difference in % change of Trec from post-HAz + HA to HTWK4 (0.6 ±â€¯1.3%; p = 0.218), however, HTWK8 (1.8 ±â€¯1.4%) was significantly greater than post-HAz + HA in HT0 (p = 0.009). CONCLUSIONS: Bi-weekly HT provided clear evidence for the ability to maintain physiological adaptions for 8 weeks following HA.

Total Body and Extracellular Water Measures Are Unrelated to Cramp Sensitivity in Euhydrated Cramp-Prone Individuals.

ABSTRACT: Earp, JE, Stearns, RL, Agostinucci, J, Lepley, AS, and Ward-Ritacco, CL. Total body and extracellular water measures are unrelated to cramp sensitivity in euhydrated cramp-prone individuals. J Strength Cond Res 36(9): 2653-2656, 2022-Spectral bioelectrical impedance analysis (BIA) is a valid and noninvasive tool for measuring total body water (TBW), intracellular water (ICW), and extracellular water (ECW). As altered hydration and electrolyte imbalance have been proposed as one of 2 etiologies for exercise-associated muscle cramps (EAMC), the purpose of this study was to determine if distribution of body water is related to cramp sensitivity in similarly hydrated cramp-prone individuals. To this end, 11 euhydrated subjects who regularly experience EAMC had their relative TBW, ICW, and ECW assessed using 8-pole spectral BIA. Subjects' cramp sensitivity was then assessed by electrically stimulating the tibial nerve at increasing frequencies until a muscle cramp occurred, allowing for the determination of the threshold frequency (TF) at which the cramp occurred. It was observed that TF was not significantly related to TBW ( r = 0.087, p = 0.368), ICW ( r = 0.105, p = 0.338), ECW ( r = 0.087, p = 0.368), or ECW:TBW ( r = 0.147, p = 0.280). As cramp etiology is poorly understood, these results add to a growing body of literature questioning the role of hydration and electrolyte imbalance in EAMC. Although fluid distribution may be unrelated to TF in those who commonly experience EAMC, additional research is needed to compare those who commonly experience cramps (athletes as well as individuals with specific neuropathies or pharmacologically induced cramps) with those who do not experience cramps and to determine if acute shifts in body water compartmentalization are related to changes in cramp sensitivity.

Heat Safety in the Workplace: Modified Delphi Consensus to Establish Strategies and Resources to Protect the US Workers.

The purpose of this consensus document was to develop feasible, evidence-based occupational heat safety recommendations to protect the US workers that experience heat stress. Heat safety recommendations were created to protect worker health and to avoid productivity losses associated with occupational heat stress. Recommendations were tailored to be utilized by safety managers, industrial hygienists, and the employers who bear responsibility for implementing heat safety plans. An interdisciplinary roundtable comprised of 51 experts was assembled to create a narrative review summarizing current data and gaps in knowledge within eight heat safety topics: (a) heat hygiene, (b) hydration, (c) heat acclimatization, (d) environmental monitoring, (e) physiological monitoring, (f) body cooling, (g) textiles and personal protective gear, and (h) emergency action plan implementation. The consensus-based recommendations for each topic were created using the Delphi method and evaluated based on scientific evidence, feasibility, and clarity. The current document presents 40 occupational heat safety recommendations across all eight topics. Establishing these recommendations will help organizations and employers create effective heat safety plans for their workplaces, address factors that limit the implementation of heat safety best-practices and protect worker health and productivity.

State-Level Implementation of Health and Safety Policies to Prevent Sudden Death and Catastrophic Injuries Within High Schools: An Update.

BACKGROUND: Mandated sports safety policies that incorporate evidence-based best practices have been shown to mitigate the risk of mortality and morbidity in sports. In 2017, a review of the state-level implementation of health and safety policies within high schools was released. PURPOSE: To provide an update on the assessment of the implementation of health and safety policies pertaining to the leading causes of death and catastrophic injuries in sports within high school athletics in the United States. STUDY DESIGN: Cross-sectional study. METHODS: A rubric composed of 5 equally weighted sections for sudden cardiac arrest, traumatic head injuries, exertional heatstroke, appropriate health care coverage, and emergency preparedness was utilized to assess an individual state's policies. State high school athletic/activities association (SHSAA) policies, enacted legislation, and Department of Education policies were extensively reviewed for all 50 states and the District of Columbia between academic year (AY) 2016-2017 (AY16/17) and 2019-2020 (AY19/20). To meet the specific rubric criteria and be awarded credit, policies needed to be mandated by all SHSAA member schools. Weighted scores were tabulated to calculate an aggregate score with a minimum of 0 and a maximum of 100. RESULTS: A total of 38 states had increased their rubric scores since AY16/17, with a mean increase of 5.57 ± 6.41 points. In AY19/20, scores ranged from 30.80 to 85.00 points compared with 23.00 to 78.75 points in AY16/17. Policies related to exertional heatstroke had the greatest change in scores (AY16/17 mean, 6.62 points; AY19/20 mean, 8.90 points; Δ = 2.28 points [11.40%]), followed by emergency preparedness (AY16/17 mean, 8.41 points; AY19/20 mean, 10.29 points; Δ = 1.88 points [9.40%]). CONCLUSION: A longitudinal review of state high school sports safety policies showed progress since AY16/17. A wide range in scores indicates that continued advocacy for the development and implementation of policies at the high school level is warranted.

Effects of Face Mask Use on Objective and Subjective Measures of Thermoregulation During Exercise in the Heat.

BACKGROUND: While increased face mask use has helped reduce COVID-19 transmission, there have been concerns about its influence on thermoregulation during exercise in the heat, but consistent, evidence-based recommendations are lacking. HYPOTHESIS: No physiological differences would exist during low-to-moderate exercise intensity in the heat between trials with and without face masks, but perceptual sensations could vary. STUDY DESIGN: Crossover study. LEVEL OF EVIDENCE: Level 2. METHODS: Twelve physically active participants (8 male, 4 female; age = 24 ± 3 years) completed 4 face mask trials and 1 control trial (no mask) in the heat (32.3°C ± 0.04°C; 54.4% ± 0.7% relative humidity [RH]). The protocol was 60 minutes of walking and jogging between 35% and 60% of relative VO2max. Rectal temperature (Trec), heart rate (HR), temperature and humidity inside and outside of the face mask (Tmicro_in, Tmicro_out, RHmicro_in, RHmicro_out) and perceptual variables (rating of perceived exertion (RPE), thermal sensation, thirst sensation, fatigue level, and overall breathing discomfort) were monitored throughout all trials. RESULTS: Mean Trec and HR increased at 30- and 60-minute time points compared with 0-minute time points, but no difference existed between face mask trials and control trials (P > 0.05). Mean Tmicro_in, RHmicro_in, and humidity difference inside and outside of the face mask (ΔRHmicro) were significantly different between face mask trials (P < 0.05). There was no significant difference in perceptual variables between face mask trials and control trials (P > 0.05), except overall breathing discomfort (P < 0.01). Higher RHmicro_in, RPE, and thermal sensation significantly predicted higher overall breathing discomfort (r2 = 0.418; P < 0.01). CONCLUSION: Face mask use during 60 minutes of low-to-moderate exercise intensity in the heat did not significantly affect Trec or HR. Although face mask use may affect overall breathing discomfort due to the changes in the face mask microenvironment, face mask use itself did not cause an increase in whole body thermal stress. CLINICAL RELEVANCE: Face mask use is feasible and safe during exercise in the heat, at low-to-moderate exercise intensities, for physically active, healthy individuals.