Impact of an Integrated Human Performance Support Group: Evaluation of Air Force Special Warfare Candidate Training and Musculoskeletal Injury Outcomes Over Eight Fiscal Years.

INTRODUCTION: The Special Warfare Training Wing and Special Warfare Human Performance Support Group (HPSG; all-co-authors) were established in fiscal year (FY) 2019 to consolidate and oversee all Air Force Special Warfare (AFSPECWAR) training and provide embedded medical and human performance support to candidates with the goal of improving graduation rates and the longevity of the AFSPECWAR operator. The purpose of this manuscript is to assess the impact of the HPSG on AFSPECWAR graduation rates, musculoskeletal injury (MSKI) incidence, and cost. MATERIALS AND METHODS: Graduation rates, MSKI incidence (including incidence density and cumulative incidence probability), and MSKI-related health care costs were assessed across all AFSPECWAR training pipelines spanning 8 FYs 2015-22, including Indoctrination, Assessment, and Selection Courses (Selection); Tactical Air Control Party (TACP); Special Tactics (ST), and Guardian Angel (GA). RESULTS: A total of 5,728 distinct candidates were assessed over the time frame. There were significant decreases in attrition when comparing the HPSG era (FY 19-22) with the prior 4-year period for the ST (47% vs. 82% graduates) and TACP (34% vs. 41% graduates) training pipelines. The corresponding Selection (36% graduates) and GA (80% graduates) pipeline attrition rates remained stable. MSKI incidence rates (both incidence density and cumulative incidence probability) overall were not significantly different when comparing the pre-HPSG and HPSG time frames; however, they varied between the two time frames by course. GA candidates had a decrease in MSKI during the apprentice course in the HPSG era compared with the pre-HPSG era (2.4-1.0 cases per 100 trainee weeks; P < .001), which corresponds to a nearly 20% reduction in the cumulative incidence probability (i.e., proportion of trainees injured) after 10 weeks of course. For ST and TACP courses, however, significantly increased incidence of MSKI was observed when comparing the two time frames (P < .001), while for Selection courses, the rates remained stable. A significant reduction in the cost of MSKI-related management (62% total relative value units, 83% total costs) was observed. CONCLUSION: The impact of the HPSG on attrition, MSKI incidence, and cost-of-care was not consistent across all training pipelines; however, taken together, there were no increases in attrition, and the cost of MSKI management was significantly lower.

Beetroot in deep waters: Navigating the risks of supplement-induced blackouts in aquatic training.

Beetroot powder, a popular athletic supplement high in nitrates, purportedly enhances exercise performance. However, recent incidents during breath-hold swims in Air Force Special Warfare training, associated with beetroot powder use, raise safety concerns. Two cases of hypoxic events prompt discussion on interactions between beetroot supplementation and cardiovascular responses to breath-hold diving, suggesting a risk for blackout. Beetroot-induced vasodilation may counteract normal cardiovascular responses during swimming, emphasizing the need for further research to quantify risks. With inconsistent dosing and lack of standardized recommendations, heightened awareness of these risks is crucial for informed decision-making regarding beetroot supplements, especially in tactical athletes.

Wearable and ingestible technology to evaluate and prevent exertional heat illness: A narrative review.

Exertional heat illness remains a constant threat to the athlete, military service member, and laborer. Recent increases in the number and intensity of environmental heat waves places these populations at an ever increasing risk and can be deadly if not recognized and treated rapidly. For this reason, it is extremely important for medical providers to guide athletes, service members, and laborers in the implementation of awareness, education, and measures to reduce or mitigate the risk of exertional heat illness. Within the past 2 decades, a variety of wearable technology options have become commercially available to track an estimation of core temperature, yet questions continue to emerge as to its use, effectiveness, and practicality in athletics, the military, and the workforce. There is a paucity of data on the accuracy of many of these newer devices in the setting of true heat stroke physiology, and it is important to avoid overreliance on new wearable technology. Further research and improvement of this technology are critical to identify accuracy in the diagnosis and prevention of EHI.

Heat stroke burden and validity of wearable-derived core temperature estimation during elite military training.

OBJECTIVES: Exertional heat stroke (EHS) remains a significant health concern while training in hot environments, prompting the development of noninvasive wearable technology for monitoring estimated core temperature (ECT). The objective of this study was to review the effectiveness of an ECT device during elite military training by providing a case series of individuals who developed EHS. METHODS: This is a retrospective study of EHS cases during high-intensity training while wearing the ECT device, Zephyr BioharnessTM. Data was collected from January 2021 through September 2021 at the Air Force Special Warfare Training pipeline in San Antonio, TX. Rectal temperatures of EHS diagnoses, defined by central nervous system (CNS) dysfunction and rectal temperature approaching or >40°C (104°F), were compared to ECT reading via Zephyr BioharnessTM. Incidence rates and psychometric properties were calculated using R package. RESULTS: A total of 47,058 daily peak ECT measurements were collected among 1,364 trainees. A total of 499 trainees flagged as potential EHS by Zephyr BioharnessTM reading >39.7°C (103.5°F). The incidence of confirmed EHS was 0.8/1000 person-months. Of the 10 confirmed EHS cases (9 males, 1 female; age = 23.4 ± 2.7 yrs; BMI = 25 ± 2; body fat = 13 ± 5%), 8 trainees had a peak ECT reading below 39.7°C which resulted in a sensitivity of 20%, specificity of 98.9%, positive likelihood ratio (LR) of 18.93 (95% Confidence Interval [CI] 5.5-65.6), and a negative LR of 0.81 (95% CI 0.6-1.1). CONCLUSION: ECT had substantial false positive and negative rates. Further studies are needed to validate this technology in other populations, and the algorithm used in this device needs to be refined to better capture the environmental and physical requirements in the special operations population.

Identifying special operative trainees at-risk for musculoskeletal injury using full body kinematics.

Introduction: Non-combat musculoskeletal injuries (MSKIs) during military training significantly impede the US military's functionality, with an annual cost exceeding $3.7 billion. This study aimed to investigate the effectiveness of a markerless motion capture system and full-body biomechanical movement pattern assessments to predict MSKI risk among military trainees. Methods: A total of 156 male United States Air Force (USAF) airmen were screened using a validated markerless biomechanics system. Trainees performed multiple functional movements, and the resultant data underwent Principal Component Analysis and Uniform Manifold And Projection to reduce the dimensionality of the time-dependent data. Two approaches, semi-supervised and supervised, were then used to identify at-risk trainees. Results: The semi-supervised analysis highlighted two major clusters with trainees in the high-risk cluster having a nearly five times greater risk of MSKI compared to those in the low-risk cluster. In the supervised approach, an AUC of 0.74 was produced when predicting MSKI in a leave-one-out analysis. Discussion: The application of markerless motion capture systems to measure an individual's kinematic profile shows potential in identifying MSKI risk. This approach offers a novel way to proactively address one of the largest non-combat burdens on the US military. Further refinement and wider-scale implementation of these techniques could bring about substantial reductions in MSKI occurrence and the associated economic costs.

Return to Duty Following Exertional Heat Stroke: A Review.

INTRODUCTION: Exertional heat stroke (EHS), which presents with extreme hyperthermia and alteration to the central nervous system, disproportionately affects the military, where warfighters are expected to perform in all types of environmental conditions. Because of an incomplete understanding of individualized recovery from EHS, there are several shortcomings with the current guidance on return to duty (RTD) following an EHS. The purpose of this manuscript is to provide an updated literature review of best practices for return to duty following EHS to guide decision making regarding EHS and explore areas of future research for medical staff who work with warfighters. MATERIALS AND METHODS: A literature review related to EHS in both athlete and military populations, as well as any existing guidelines for RTD, was conducted using PubMed and Covidence. RESULTS: Twenty-one articles were identified for this updated review on EHS and RTD, with recommendations focused during and after an EHS event, as well as the role of heat tolerance testing (HTT). CONCLUSIONS: EHS has a high morbidity and mortality rate if not treated rapidly. Because the extent of end-organ damage is dependent on the amount of time that the individual is hyperthermic, rapid diagnosis via rectal thermometry, and efficient cooling methods are imperative to the wellbeing of EHS patients. Following EHS, gradual RTD recommendations within the limits of operational demand should be implemented to reduce the risk for a subsequent heat injury event. While many versions of HTT, most notably the Israeli Defense Force (IDF) protocol, have been created to guide RTD recommendations, a universal assessment for heat tolerance has yet to be adopted. As such, medical personnel should apply a multifactorial approach to ensure safe RTD.

Carbon Fiber Insoles Enhance Perception of Performance Despite Variable Objective Outcomes: Specific to the Moderately Active Individual.

Carbon fiber insoles (CFIs) may benefit performance in elite athletes, however, their use in moderately active individuals has been adopted without evidence supporting such enhancements in this population. Fifteen male subjects performed vertical jump (VJ) and repeat treadmill sprint tests before and after a VO2peak while wearing 1) CFIs and 2) control insoles (CON). Subjects completed a subjective survey regarding their perceived performance abilities for both conditions. There were no significant differences between CFIs and CON in VJ height, sprint distance, heart rate following sprints; and rate of oxygen consumption, perceived fatigue, and perceived exertion at 85% of maximal speed (p > 0.05) during the VO2peak. At maximal speed, although there was no difference between conditions in peak rate of oxygen consumption (95%CI [-4.85, 0.21]) and respiratory exchange ratio (95%CI [-0.01, 0.03]), CFIs resulted in a reduced level of perceived fatigue (95%CI [-1, 0]) and perceived exertion (95%CI [-2, 0]) compared to CON. Subjects subjectively reported increased feelings of "propulsion or explosiveness" (p = 0.026) and being able to "perform better while jumping" (p = 0.029) while wearing CFIs. Heightened perceptions of performance enhancements when wearing CFIs indicate, in the moderately active, perceptual benefits could be more influential for determining CFI use.

Physical Profile of Air Force Special Warfare Trainees.

Physical fitness testing in the military is commonly used to assess whether service members are physically capable of performing the diverse physical tasks that may be required for their job. Body composition can influence an individual's ability to physically perform. This study aimed to analyze the general physical profile of U.S. Air Force (USAF) special warfare candidates by assessing body composition results and physical assessment scores collected over the past four years. Male candidates (n = 1036) were 18.2 years to 39.5 years of age (M = 23.5, SD = 3.9) and weighed 78.8 kg (SD = 8.3) with a BMI of 25.0 (SD = 2.0) at 11.8% body fat (SD = 3.3) as measured using bioelectrical impedance. Body composition and fitness scores were similar to those noted in U.S. Navy special warfare candidates as well as individuals in other elite tactical units. These results highlight the normative body composition profile of individuals assessing for advanced military career fields.

Management of a Special Warfare Trainee With Repeat Exertional Heat Stroke: A Case Study.

CONTEXT: Exertional heat stroke (EHS) is the most deadly form the exertional heat illness with a higher incidence among active duty US military members than in the general population. Current guidelines on EHS recovery timelines and return to duty vary among the military branches. In some cases, individuals experience prolonged heat and exercise intolerance with repeat exertional heat illness events, which can complicate the recovery process. Management and rehabilitation of such individuals is unclear. CASE PRESENTATION: This manuscript addresses the case and management of a US Air Force Special Warfare trainee who experienced 2 episodes of EHS, despite early recognition, gold standard treatment, and undergoing 4 weeks of a stepwise recovery after an initial EHS. MANAGEMENT AND OUTCOMES: After the second episode, a 3-step process was utilized, consisting of a prolonged and personalized recovery period, heat tolerance testing using Israeli Defense Force advanced modeling, and stepwise reacclimatization. This process allowed the trainee to successfully recover from repeat EHS and return to duty, and set a framework for future repeat EHS treatment guidelines. CONCLUSIONS: In individuals with repeat EHS, a prolonged recovery period followed by heat tolerance testing can be used to demonstrate appropriate thermotolerance and safely clear an individual to begin stepwise reacclimatization. Overall, patient care and military readiness may be improved by unified Department of Defense guidelines for return to duty after EHS.

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.

Current Clinical Concepts: Heat Tolerance Testing.

Heat tolerance testing (HTT) has been developed to assess readiness for work or exercise in the heat based on thermoregulation during exertion. Although the Israeli Defense Forces protocol has been the most widely used and referenced, other protocols and variables considered in the interpretation of the testing are emerging. Our purpose was to summarize the role of HTT after exertional heat stroke; assess the validity of HTT; and provide a review of best-practice recommendations to guide clinicians, coaches, and researchers in the performance, interpretation, and future direction of HTT. We also offer the strength of evidence for these recommendations using the Strength of Recommendation Taxonomy system.

Blood Flow Restriction Therapy for Use After Extremity Fracture: A Critically Appraised Topic.

CLINICAL SCENARIO: Blood flow restriction (BFR) therapy has emerged as a viable treatment option to enhance clinical recovery in patients with primarily muscular injuries. However, BFR therapy has been rarely investigated in patients with osseous injuries to include extremity fracture. FOCUSED CLINICAL QUESTION: Does BFR-enhanced therapy improve clinical outcomes in patients during the acute to subacute rehabilitation period after extremity fracture? SUMMARY OF KEY FINDINGS: (1) In cases of 2 high-performing athletes with talus and osteochondral fracture of the knee, BFR was well tolerated and an effective rehabilitation regimen. (2) In 2 randomized controlled trials evaluating BFR use in patients after operative and nonoperative management of distal radius fractures, pain with activity and self-perceived function were improved in BFR-enhanced therapy as compared with a standard rehabilitation regimen. (3) Objective clinical outcomes including radiographic healing, extremity range of motion, and grip strength evaluated by the randomized controlled trials did not differ significantly between the BFR-enhanced and standard rehabilitation groups. CLINICAL BOTTOM LINE: BFR-enhanced therapy may improve pain and self-perceived function of the injured extremity during the acute to subacute rehabilitation period after fracture. However, there is not yet a demonstrated benefit of BFR on hastening objective measures of clinical recovery. Large-scale clinical trials comparing BFR-enhanced rehabilitation with standard rehabilitation regimens are needed to better characterize BFR use in patients with osseous injuries. STRENGTH OF RECOMMENDATION: Two case reports and 2 randomized controlled trials provide level IIB evidence suggesting that BFR may improve pain in the acute rehabilitative stage and improve the patient's perceived function of the injured extremity, without greater improvement in objectively measured clinical parameters as compared with a standard rehabilitation regimen.

Force plate vertical jump scans are not a valid proxy for physical fitness in US special warfare trainees.

Background: The United States Air Force Special Warfare Training Wing (SWTW) administers a comprehensive physical fitness test to active duty Airmen entering the Special Warfare training pipeline. The Sparta Science™ system utilizes proprietary software to analyze the force-time curve of a vertical jump and purports to serve as a proxy for traditional military fitness tests. The Sparta Science™ system produces four proprietary metrics, including the Sparta™ Score, which is correlated to high magnitudes of force production purportedly performance. This study investigated how Sparta™ Jump Scans correlate to components of a physical fitness test utilized within the SW training pipeline. Methods: At the entry and exit of an 8-week Special Warfare Training Wing preparatory course (SW PREP), 643 trainees completed both an initial and final Sparta™ Jump Scan and a Candidate Fitness Test (CFT). The Candidate Fitness Test consists of eight components and tests several different domains of fitness including strength, power, muscular endurance, swimming proficiency, and cardiovascular fitness. Paired t-tests were used to determine if Sparta™ Jump Scan metrics and CFT components changed during SW PREP. Sparta™ Score's correlation was assessed against every other Sparta™ Jump Scan metric and all CFT fitness measures. Results: This study found that the Sparta™ Jump Scan metrics decline slightly over SW PREP (p < 0.05; negligible-small effect size), while most CFT measures improve (p < 0.05; small-medium effect size). Changes in Sparta™ Jump Scan metrics did not reflect the changes in CFT performance over SW PREP (r 2: 0.00-0.03). Conclusion: The Sparta™ Score was not correlated to the most tactically-relevant fitness measures (rucking and swimming), and only weakly correlated with the only jumping measure on the fitness test, the standing broad jump.

Musculoskeletal Injuries During U.S. Air Force Special Warfare Training Assessment and Selection, Fiscal Years 2019-2021.

From the inception of the Special Warfare Training Wing in fiscal year 2019 through 2021, 753 male, enlisted candidates attempted at least 1 Assessment and Selection and did not self-eliminate (i.e., quit). Candidates were on average 23 years of age. During candidates' first attempt, 356 (47.3%) individuals experienced a musculoskeletal (MSK) injury. Among the injuries, the most frequent type was nonspecific (n=334/356; 93.8%), and the most common anatomic region of injury was the lower extremity (n=255/356; 71.6%). When included in a multivariable model, older age, slower run times on initial fitness tests, and prior nonspecific injury were associated with both any injury and specifically lower extremity MSK injury.

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.

Corrigendum: Estrogen to Progesterone Ratio and Fluid Regulatory Responses to Varying Degrees and Methods of Dehydration.

[This corrects the article DOI: 10.3389/fspor.2021.722305.].

Deaths Among U.S. Air Force Basic Military Trainees, 2008-2020.

INTRODUCTION: The U.S. Air Force (USAF) Basic Military Training (BMT), a rigorous training program for all enlisted members of the USAF, trains roughly 36,000 recruits annually. Transforming civilians into ready warrior airmen has inherent risks to trainee health, which has infrequently included death. While the average death rate at USAF BMT has decreased between 1956 and 2007 due to process improvement and preventive medicine efforts, further review is warranted to examine the deaths that have occurred since the last published period (1997-2007) and to determine the impact policy changes and updates have had on death rates since that time. Therefore, the purpose of this paper is to identify death rates and types from 2008 to 2020, explore policy implementation, and identify areas needing further improvement or modifications to the overall safety, fitness, and health of USAF BMT trainees. MATERIALS AND METHODS: All deaths were examined and reviewed from 2008 through 2020 for trainees attending the USAF BMT using medical records and autopsy reports. Death rates were calculated using the total population of trainees in a given year as well as over the entire 13-year study period. RESULTS: From 2008 to 2020, five deaths occurred among USAF BMT trainees (one cardiac, two exertional sickling due to sickle cell trait, one infection, and one suicide). This resulted in an overall average death rate of 1.08 per 100,000 trainees, as compared to 1.46 per 100,000 from 1997 to 2007. The last death in the study period occurred in 2016. CONCLUSION: A modest downward trend of average death rate has continued since 2007, and no deaths from 2016 through 2020 represents the longest time frame without any deaths at USAF BMT over all times reported (dating back to 1956) which suggest that emergency best practice policies are/have improved. However, cardiac death rate and suicide rate have not changed since the last report. Policies and practices should be continuously reviewed and refined to reduce the risk of death at USAF BMT.

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.

Estrogen to Progesterone Ratio and Fluid Regulatory Responses to Varying Degrees and Methods of Dehydration.

The purpose of this study was to investigate the relationship between volume regulatory biomarkers and the estrogen to progesterone ratio (E:P) prior to and following varying methods and degrees of dehydration. Ten women (20 ± 1 year, 56.98 ± 7.25 kg, 164 ± 6 cm, 39.59 ± 2.96 mL•kg•min-1) completed four intermittent exercise trials (1.5 h, 33.8 ± 1.3°C, 49.5 ± 4.3% relative humidity). Testing took place in two hydration conditions, dehydrated via 24-h fluid restriction (Dehy, USG > 1.020) and euhydrated (Euhy, USG ≤ 1.020), and in two phases of the menstrual cycle, the late follicular phase (days 10-13) and midluteal phase (days 18-22). Change in body mass (%BMΔ), serum copeptin concentration, and plasma osmolality (Posm) were assessed before and after both dehydration stimuli (24-h fluid restriction and exercise heat stress). Serum estrogen and progesterone were analyzed pre-exercise only. Estrogen concentration did not differ between phases or hydration conditions. Progesterone was significantly elevated in luteal compared to follicular in both hydration conditions (Dehy-follicular: 1.156 ± 0.31, luteal: 5.190 ± 1.56 ng•mL-1, P < 0.05; Euhy-follicular: 0.915 ± 0.18, luteal: 4.498 ± 1.38 ng·mL-1, P < 0.05). As expected, E:P was significantly greater in the follicular phase compared to luteal in both hydration conditions (Dehy-F:138.94 ± 89.59, L: 64.22 ± 84.55, P < 0.01; Euhy-F:158.13 ± 70.15, L: 50.98 ± 39.69, P < 0.01, [all •103]). Copeptin concentration was increased following 24-h fluid restriction and exercise heat stress (mean change: 18 ± 9.4, P < 0.01). We observed a possible relationship of lower E:P and higher copeptin concentration following 24-h fluid restriction (r = -0.35, P = 0.054). While these results did not reach the level of statistical significance, these data suggest that the differing E:P ratio may alter fluid volume regulation during low levels of dehydration but have no apparent impact after dehydrating exercise in the heat.