Relationship Between Running Biomechanics and Core Temperature Across a Competitive Road Race.

BACKGROUND: Outdoor races introduce environmental stressors to runners, and core temperature changes may influence runners' movement patterns. This study assessed changes and determined relationships between sensor-derived running biomechanics and core temperature among runners across an 11.27-km road race. HYPOTHESIS: Core temperatures would increase significantly across the race, related to changes in spatiotemporal biomechanical measures. STUDY DESIGN: Cross-sectional cohort study. LEVEL OF EVIDENCE: Level 3. METHODS: Twenty runners (9 female, 11 male; age, 48 ± 12 years; height, 169.7 ± 9.1 cm; mass, 71.3 ± 13.4 kg) enrolled in the 2022 Falmouth Road Race were recruited. Participants used lightweight technologies (ingestible thermistors and wearable sensors) to monitor core temperature and running biomechanics throughout the race. Timestamps were used to align sensor-derived measures for 7 race segments. Observations were labeled as core temperatures generally within normal limits (<38°C) or at elevated core temperatures (≥38°C). Multivariate repeated measures analyses of variance were used to assess changes in sensor-derived measures across the race, with Bonferroni post hoc comparisons for significant findings. Pearson's r correlations were used to assess the relationship between running biomechanics and core temperature measures. RESULTS: Eighteen participants developed hyperthermic core temperatures (39.0°C ± 0.5°C); core temperatures increased significantly across the race (P < 0.01). Kinetic measures obtained from the accelerometers, including shock, impact, and braking g, all significantly increased across the race (P < 0.01); other sensor-derived biomechanical measures did not change significantly. Core temperatures were weakly associated with biomechanics (|r range|, 0.02-0.16). CONCLUSION: Core temperatures and kinetics increased significantly across a race, yet these outcomes were not strongly correlated. The observed kinetic changes may have been attributed to fatigue-related influences over the race. CLINICAL RELEVANCE: Clinicians may not expect changes in biomechanical movement patterns to signal thermal responses during outdoor running in a singular event.

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 (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.

Proper Recognition and Management of Exertional Heat Stroke in a High School Cross-Country Runner: A Validation Clinical Case Report.

A 14-year-old female high school cross- country runner (height = 154 cm, mass = 48.1 kg) with no history of exertional heat stroke (EHS) collapsed at the end of a race. An athletic trainer assessed the patient, who presented with difficulty breathing and then other signs of EHS (eg, confusion and agitation). The patient was taken to the medical area and draped with a towel, and a rectal temperature (Tre) of 106.9°F (41.6°C) was obtained. The emergency action plan was activated, and emergency medical services was called. The patient was submerged in a cold-water immersion tub until emergency medical services arrived (∼15 minutes; Tre = 100.1°F; cooling rate: 0.41°F.min-1[0.25°C.min-1]). At the hospital, the patient received intravenous fluids, and urine and blood tests were normal. She was not admitted and returned to running without sequelae. Following best practices, secondary school athletic trainers can prevent deaths from EHS by properly recognizing the condition and providing rapid cooling before transport.

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.

Availability of a Flavored Beverage and Impact on Children's Hydration Status, Sleep, and Mood.

Euhydration remains a challenge in children due to lack of access and unpalatability of water and to other reasons. The purpose of this study was to determine if the availability/access to a beverage (Creative Roots®) influences hydration in children and, therefore, sleep quality and mood. Using a crossover investigation, 46 participants were randomly assigned to a control group (CON) or an intervention group and received Creative Roots® (INT) for two-week periods. We recorded daily first morning and afternoon urine color (Ucol), thirst perception, and bodyweight of the two groups. Participants reported to the lab once per week and provided first morning urine samples to assess Ucol, urine specific gravity (USG), and urine osmolality (Uosmo). Participants also completed the questionnaires Profile of Mood States-Adolescents (POMS-a) and Pittsburgh Sleep Quality Index (PSQI). Dependent t-tests were used to assess the effects of the intervention on hydration, mood, and sleep quality. Uosmo was greater and Ucol was darker in the control group (mean ± SD) [Uosmo: INT = 828 ± 177 mOsm·kg-1, CON = 879 ± 184 mOsm·kg-1, (p = 0.037], [Ucol:INT = 5 ± 1, CON = 5 ± 1, p = 0.024]. USG, POMS-a, and PSQI were not significant between the groups. At-home daily afternoon Ucol was darker in the control group [INT = 3 ± 1, CON = 3 ± 1, p = 0.022]. Access to Creative Roots® provides a small, potentially meaningful hydration benefit in children. However, children still demonstrated consistent mild dehydration based on Uosmo, despite consuming the beverage.

Heat Acclimation Following Heat Acclimatization Elicits Additional Physiological Improvements in Male Endurance Athletes.

The purpose of this study was to assess the effectiveness of heat acclimatization (HAz) followed by heat acclimation (HA) on physiological adaptations. 25 male endurance athletes (age 36 ± 12 y, height 178.8 ± 6.39 cm, body mass 73.03 ± 8.97 kg, and VO2peak 57.5 ± 7.0 mL·kg-1·min-1) completed HAz and HA. HAz was 3 months of self-directed summer training. In the laboratory, a 5-day HA prescribed exercise to target a hyperthermic zone (HZHA) of Trec between 38.50 and 39.75 °C for 60 min. Exercise trials were 60 min of running (59% ± 2% VO2peak) in an environmental chamber (wet bulb globe temperature 29.53 ± 0.63 °C) and administered at: baseline, post-HAz, and post-HAz+HA. Measured variables included internal body temperature (Trec), heart rate (HR), and sweat rate (SR). Repeated measure ANOVAs and post hoc comparisons were used to assess statistically significant (p < 0.05) differences. Trec was lower post-HAz+HA (38.03 ± 0.39 °C) than post-HAz (38.25 ± 0.42 °C, p = 0.009) and baseline (38.29 ± 0.37 °C, p = 0.005). There were no differences between baseline and post-HAz (p = 0.479) in Trec. HR was lower post-HAz (143 ± 12 bpm, p = 0.002) and post-HAz+HA (134 ± 11 bpm, p < 0.001) than baseline (138 ± 14 bpm). HR was lower post-HAz+HA than post-HAz (p = 0.013). SR was higher post-HAz+HA (1.93 ± 0.47 L·h-1) than post-HAz (1.76 ± 0.43 L·h-1, p = 0.027). Combination HAz and HA increased physiological outcomes above HAz. This method can be used to improve performance and safety in addition to HAz alone.

Emergency Medical Service Directors' Protocols for Exertional Heat Stroke.

Background and Objectives: Emergency Medical Service (EMS) protocols vary widely and may not implement best practices for exertional heat stroke (EHS). EHS is 100% survivable if best practices are implemented within 30 min. The purpose of this study is to compare EMS protocols to best practices for recognizing and treating EHS. Materials and Methods: Individuals (n = 1350) serving as EMS Medical or Physician Director were invited to complete a survey. The questions related to the EHS protocols for their EMS service. 145 individuals completed the survey (response rate = 10.74%). Chi-Squared Tests of Associations (χ2) with 95% confidence intervals (CI) were calculated. Prevalence ratios (PR) with 95% CI were calculated to determine the prevalence of implementing best practices based on location, working with an athletic trainer, number of EHS cases, and years of directing. All PRs whose 95% CIs excluded 1.00 were considered statistically significant; Chi-Squared values with p values < 0.05 were considered statistically significant. Results: A majority of the respondents reported not using rectal thermometry for the diagnosis of EHS (n = 102, 77.93%) and not using cold water immersion for the treatment of EHS (n = 102, 70.34%). If working with an athletic trainer, EMS is more likely to implement best-practice treatment (i.e., cold-water immersion and cool-first transport-second) (69.6% vs. 36.9%, χ2 = 8.480, p < 0.004, PR = 3.15, 95% CI = 1.38, 7.18). Conclusions: These findings demonstrate a lack of implementation of best-practice standards for EHS by EMS. Working with an athletic trainer appears to increase the likelihood of following best practices. Efforts should be made to improve EMS providers' implementation of best-practice standards for the diagnosis and management of EHS to optimize patient outcomes.