Robert A. Huggins

Exertional heat stroke: new concepts regarding cause and care

Abstract When athletes, warfighters, and laborers perform intense exercise in the heat, the risk of exertional heat stroke (EHS) is ever present. The recent data regarding the fatalities due to EHS within the confines of organized American sport are not promising: during the past 35 years, the highest number of deaths in a 5-year period occurred from 2005 to 2009. This reminds us that, regardless of the advancements of knowledge in the area of EHS prevention, recognition, and treatment, knowledge has not been translated into practice. This article addresses important issues related to EHS cause and care. We focus on the predisposing factors, errors in care, physiology of cold water immersion, and return-to-play or duty considerations.

The inter-association task force for preventing sudden death in secondary school athletics programs: best-practices recommendations.

Douglas J. Casa, PhD, ATC, FNATA, FACSM (Chair)*†; Jon Almquist, VATL, ATC*; Scott A. Anderson, ATC*; Lindsay Baker, PhD‡; Michael F. Bergeron, PhD, FACSM§; Brian Biagioli, EdD||; Barry Boden, MD¶; Joel S. Brenner, MD, MPH, FAAP#; Michael Carroll, MEd, LAT, ATC*; Bob Colgate**; Larry Cooper, MS, LAT, ATC*; Ron Courson, PT, ATC, NREMT-I, CSCS*; David Csillan, MS, LAT, ATC*; Julie K. DeMartini, MA, ATC†; Jonathan A. Drezner, MD††; Tim Erickson, CAA‡‡; Michael S. Ferrara, PhD, ATC, FNATA*; Steven J. Fleck, PhD, CSCS, FNSCA, FACSM§§; Rob Franks, DO, FAOASM||||; Kevin M. Guskiewicz, PhD, ATC, FNATA, FACSM*; William R. Holcomb, PhD, LAT, ATC, CSCS*D, FNATA, FNSCA§§; Robert A. Huggins, MEd, ATC†; Rebecca M. Lopez, PhD, ATC, CSCS†; Thom Mayer, MD, FACEP¶¶; Patrick McHenry, MA, CSCS*D, RSCC§§; Jason P. Mihalik, PhD, CAT(C), ATC##; Francis G. O’Connor, MD, MPH, FACSM††; Kelly D. Pagnotta, MA, ATC, PES†; Riana R. Pryor, MS, ATC†; John Reynolds, MS, VATL, ATC*; Rebecca L. Stearns, PhD, ATC†; Verle Valentine, MD††

Assessment of hydration biomarkers including salivary osmolality during passive and active dehydration

BACKGROUND/OBJECTIVES:Hydration state can be assessed via body mass change (BMΔ), serum and urine osmolality (Sosm, Uosm), urine-specific gravity (Usg) and urine volume (Uvol). As no hydration index has been shown to be valid in all circumstances, value exists in exploring novel biomarkers such as salivary osmolality (Vosm). Utilizing acute BMΔ as the reference standard, this research examined the efficacy of Sosm, Vosm, Uosm, Uvol and Usg, during passive (PAS) and active (ACT) heat exposure.SUBJECTS/METHODS:Twenty-three healthy men (age, 22±3 years; mass, 77.3±12.8 kg; height, 179.9±8.8cm; body fat, 10.6±4.5%) completed two randomized 5-h dehydration trials (36±1 °C). During PAS, subjects sat quietly, and during ACT, participants cycled at 68±6% maximal heart rate. Investigators measured all biomarkers at each 1% BMΔ.RESULTS:Average mass loss during PAS was 1.4±0.3%, and 4.1±0.7% during ACT. Significant between-treatment differences at −1% BMΔ were observed for Sosm (PAS, 296±4; ACT, 301±4 mOsm/kg) and Uosm (PAS, 895±207; ACT, 661±192 mOsm/kg). During PAS, only Uosm, Uvol and Usg increased significantly (−1 and −2% BMΔ versus baseline). During ACT, Vosm most effectively diagnosed dehydration ⩾2% (sensitivity=86%; specificity=91%), followed by Sosm (sensitivity=83%; specificity=83%). Reference change values were validated for Sosm, Usg and BMΔ.CONCLUSIONS:The efficacy of indices to detect dehydration ⩾2% differed across treatments. At rest (PAS), only urinary indices increased in concert with body water loss. During exercise (ACT), Sosm and Vosm exhibited the highest sensitivity and specificity. Sosm, Usg and BMΔ exhibited validity in serial measurements. These findings indicate hydration biomarkers should be selected by considering daily activities.

Comparison of rectal and aural core body temperature thermometry in hyperthermic, exercising individuals: a meta-analysis.

OBJECTIVE To compare mean differences in core body temperature (T(core)) as assessed via rectal thermometry (T(re)) and aural thermometry (T(au)) in hyperthermic exercising individuals. DATA SOURCES PubMed, Ovid MEDLINE, SPORTDiscus, CINAHL, and Cochrane Library in English from the earliest entry points to August 2009 using the search terms aural, core body temperature, core temperature, exercise, rectal, temperature, thermistor, thermometer, thermometry, and tympanic. Study Selection: Original research articles that met these criteria were included: (1) concurrent measurement of T(re) and T(au) in participants during exercise, (2) minimum mean temperature that reached 38°C by at least 1 technique during or after exercise, and (3) report of means, standard deviations, and sample sizes. DATA EXTRACTION Nine articles were included, and 3 independent reviewers scored these articles using the Physiotherapy Evidence Database (PEDro) scale (mean = 5.1 ± 0.4). Data were divided into time periods pre-exercise, during exercise (30 to 180 minutes), and postexercise, as well as T(re) ranges <37.99°C, 38.00°C to 38.99°C, and >39.00°C. Means and standard deviations for both measurement techniques were provided at all time intervals reported. Meta-analysis was performed to determine pooled and weighted mean differences between T(re) and T(au). DATA SYNTHESIS The T(re) was conclusively higher than the T(au) pre-exercise (mean difference [MD] = 0.27°C, 95% confidence interval [CI] = 0.15°C, 0.39°C), during exercise (MD = 0.96°C, 95% CI = 0.84°C, 1.08°C), and postexercise (MD = 0.71°C, 95% CI = 0.65°C, 0.78°C). As T(re) measures increased, the magnitude of difference between the techniques also increased with an MD of 0.59°C (95% CI = 0.53°C, 0.65°C) when T(re) was <38°C; 0.79°C (95% CI = 0.72°C, 0.86°C) when T(re) was between 38.0°C and 38.99°C; and 1.72°C (95% CI = 1.54°, 1.91°C) when T(re) was >39.0°C. CONCLUSIONS The T(re) was consistently greater than T(au) when T(core) was measured in hyperthermic individuals before, during, and postexercise. As T(core) increased, T(au) appeared to underestimate T(core) as determined by T(re). Clinicians should be aware of this critical difference in temperature magnitude between these measurement techniques when assessing T(core) in hyperthermic individuals during or postexercise.

Hypohydration and hyperthermia impair neuromuscular control after exercise.

PURPOSE This study aimed to evaluate the effects of hypohydration and hyperthermia during exercise on movement technique and postural control. METHODS Twelve healthy men (age = 20 ± 2 yr, height = 182 ± 8 cm, mass = 74.0 ± 8.2 kg, V˙O2max = 57.0 ± 6.0 mL·kg·min; mean ± SD) completed four randomized test sessions: euhydrated temperate (EUT), euhydrated hot (EUH), hypohydrated temperate (HYT), and hypohydrated hot (HYH). Temperate and hot conditions were performed in 18.0°C ± 0.2°C, 50.0% ± 3.5% relative humidity, and 34.0°C ± 0.3°C, 45.0% ± 4.5% relative humidity, respectively. Movement technique and postural control were assessed before exercise (PRE), after exercise (POST), and after recovery (REC). Movement technique was evaluated using the Landing Error Scoring System (LESS). Postural control was assessed using the Balance Error Scoring System (BESS) and center-of-pressure sway velocity (SV) and elliptical sway area (ESA) during a dynamic balance test. The 90-min treadmill exercise protocol (1.34-1.78 m·s; 5% grade) required subjects to walk carrying a 20.5-kg rucksack. Subjects sat quietly in the test environment during a 60-min recovery period after exercise. Repeated-measures ANOVAs with a Tukey-HSD post hoc test evaluated differences between time and condition for dependent variables. RESULTS Exercise during HYH significantly increased LESS scores (PRE = 3.72 ± 1.73, POST = 4.42 ± 1.75) compared with HYT (3.75 ± 1.76) and EUH (3.61 ± 1.71) (P < 0.05). LESS scores remained elevated during REC for HYH compared with EUT (4.39 ± 1.47 vs 3.47 ± 2.05, P < 0.05). The HYH condition caused the greatest number of BESS errors (P = 0.02), largest ESA (P < 0.05), and highest SV (P = 0.02). Regardless of the condition, participants had the most BESS errors (P = 0.002) and highest SV (P = 0.003) during POST compared with the PRE and REC. CONCLUSIONS Hypohydration during exercise in the heat impairs neuromuscular control. These findings suggest that physical activity in the heat while dehydrated may affect parameters associated with a higher risk of injury.

Influence of Body Mass Loss on Changes in Heart Rate During Exercise in the Heat: A Systematic Review

Adams, WM, Ferraro, EM, Huggins, RA, and Casa, DJ. Influence of body mass loss on changes in heart rate during exercise in the heat: A systematic review. J Strength Cond Res 28(8): 2380–2389, 2014—The purpose of this review was to compare the changes in heart rate (HR) for every 1% change in body mass loss (&Dgr;BML) in individuals while exercising in the heat. PubMed, SPORTDiscus, ERIC, CINAHL, and Scopus were searched from the earliest entry to February 2013 using the search terms dehydration, heart rate, and exercise in various combinations. Original research articles that met the following criteria were included: (a) valid measure of HR, (b) exercise in the heat (>26.5° C [79.7 °F]), (c) the level of dehydration reached at least 2%, (d) a between-group comparison (a euhydrated group or a graded dehydration protocol) was evident, and (e) for rehydration protocols, only oral rehydration was considered for inclusion. Twenty articles were included in the final analysis. Mean values and SDs for HR and percentage of body mass loss immediately after exercise were used for this review. The mean change in HR for every 1% &Dgr;BML was 3 b·min−1. In trials where subjects arrived euhydrated and hypohydrated, the mean change in HR for every 1% &Dgr;BML was 3 and 3 b·min—1, respectively. Fixed intensity and variable intensity trials exhibited a mean HR change of 4 and 1 b·min−1, respectively. Exercising in the heat while hypohydrated (≥2%) resulted in an increased HR after exercise. This increase in HR for every 1% &Dgr;BML exacerbates cardiovascular strain in exercising individuals, thus causing decrements in performance. It should be encouraged that individuals should maintain an adequate level of hydration to maximize performance, especially in the heat.

Maximizing Athletic Performance in the Heat

ABSTRACT ATHLETES TRAIN AND PERFORM AT OPTIMAL LEVELS IN COOL ENVIRONMENTS; HOWEVER, MANY INDIVIDUALS DO NOT ALTER THEIR TRAINING IN HOT ENVIRONMENTS. THE PURPOSE OF THIS REVIEW IS TO EXPLORE EXISTING RESEARCH RELATED TO ENHANCING PERFORMANCE IN THE HEAT BY MODIFYING THE FOLLOWING PRACTICES: (A) HYDRATION, (B) BODY COOLING, (C) HEAT ACCLIMATIZATION, (D) CLOTHING AND PROTECTIVE EQUIPMENT, (E) NUTRITION AND SUPPLEMENTATION, (F) SLEEP, AND (G) TECHNOLOGY. THIS REVIEW EXPLORES PRACTICAL WAYS ATHLETES CAN CHANGE THEIR EXERCISE HABITS WITH THE GOAL OF INCREASING PERFORMANCE IN HOT ENVIRONMENTS.

Effects of heat acclimation on hand cooling efficacy following exercise in the heat

ABSTRACT This study examined the separate and combined effects of heat acclimation and hand cooling on post-exercise cooling rates following bouts of exercise in the heat. Seventeen non-heat acclimated (NHA) males (mean ± SE; age, 23 ± 1 y; mass, 75.30 ± 2.27 kg; maximal oxygen consumption [VO2 max], 54.1 ± 1.3 ml·kg−1·min−1) completed 2 heat stress tests (HST) when NHA, then 10 days of heat acclimation, then 2 HST once heat acclimated (HA) in an environmental chamber (40°C; 40%RH). HSTs were 2 60-min bouts of treadmill exercise (45% VO2 max; 2% grade) each followed by 10 min of hand cooling (C) or no cooling (NC). Heat acclimation sessions were 90–240 min of treadmill or stationary bike exercise (60–80% VO2 max). Repeated measures ANOVA with Fishers LSD post hoc (α < 0.05) identified differences. When NHA, C (0.020 ± 0.003°C·min−1) had a greater cooling rate than NC (0.013 ± 0.003°C·min−1) (mean difference [95%CI]; 0.007°C [0.001,0.013], P = 0.035). Once HA, C (0.021 ± 0.002°C·min−1) was similar to NC (0.025 ± 0.002°C·min−1) (0.004°C [−0.003,0.011], P = 0.216). Hand cooling when HA (0.021 ± 0.002°C·min−1) was similar to when NHA (0.020 ± 0.003°C·min−1) (P = 0.77). In conclusion, when NHA, C provided greater cooling rates than NC. Once HA, C and NC provided similar cooling rates.

Best practice recommendations for prevention of sudden death in secondary school athletes: an update.

The aim of the recent Inter-Association Task Force held in Washington, D.C. at the 2013 Youth Safety Summit determined best practice recommendations for preventing sudden death in secondary school athletics. This document highlights the major health and safety practices and policies in high school athletics that are paramount to keep student athletes safe. The purpose of this commentary is to review the findings of the document developed by the task force and to provide possible areas where research is needed to continue to educate medical practitioners, players, coaches, and parents on ways to prevent tragedies from occurring during sport.

Exertional heat illness incidence and on-site medical team preparedness in warm weather

To investigate the influence of estimated wet bulb globe temperature (WBGT) and the International Institute of Race Medicine (IIRM) activity modification guidelines on the incidence of exertional heat stroke (EHS) and heat exhaustion (HEx) and the ability of an on-site medical team to treat those afflicted. Medical records of EHS and HEx patients over a 17-year period from the New Balance Falmouth Road Race were examined. Climatologic data from nearby weather stations were obtained to calculate WBGT with the Australian Bureau of Meteorology (WBGTA) and Liljegren (WBGTL) models. Incidence rate (IR) of EHS, HEx, and combined total of EHS and HEx (COM) were calculated, and linear regression analyses were performed to assess the relationship between IR and WBGTA or WBGTL. One-way ANOVA was performed to compare differences in EHS, HEx, and COM incidence to four alert levels in the IIRM guidelines. Incidence of EHS, HEx, and COM was 2.12, 0.98, and 3.10 cases per 1000 finishers. WBGTA explained 48, 4, and 46% of the variance in EHS, HEx, and COM IR; WBGTL explained 63, 13, and 69% of the variance in EHS, HEx, and COM IR. Main effect of WBGTA and WBGTL on the alert levels were observed in EHS and COM IR (p < 0.05). The cumulative number of EHS patients treated did not exceed the number of cold water immersion tubs available to treat them. EHS IR increased as WBGT and IIRM alert level increased, indicating the need for appropriate risk mitigation strategies and on-site medical treatment.