Kevin C. Miller

National Athletic Trainers' Association Position Statement: Exertional Heat Illnesses.

OBJECTIVE To present best-practice recommendations for the prevention, recognition, and treatment of exertional heat illnesses (EHIs) and to describe the relevant physiology of thermoregulation. BACKGROUND Certified athletic trainers recognize and treat athletes with EHIs, often in high-risk environments. Although the proper recognition and successful treatment strategies are well documented, EHIs continue to plague athletes, and exertional heat stroke remains one of the leading causes of sudden death during sport. The recommendations presented in this document provide athletic trainers and allied health providers with an integrated scientific and clinically applicable approach to the prevention, recognition, treatment of, and return-to-activity guidelines for EHIs. These recommendations are given so that proper recognition and treatment can be accomplished in order to maximize the safety and performance of athletes. RECOMMENDATIONS Athletic trainers and other allied health care professionals should use these recommendations to establish onsite emergency action plans for their venues and athletes. The primary goal of athlete safety is addressed through the appropriate prevention strategies, proper recognition tactics, and effective treatment plans for EHIs. Athletic trainers and other allied health care professionals must be properly educated and prepared to respond in an expedient manner to alleviate symptoms and minimize the morbidity and mortality associated with these illnesses.

Exercise-Associated Muscle Cramps: Causes, Treatment, and Prevention

Context: Exercise-associated muscle cramps (EAMC) are a common condition experienced by recreational and competitive athletes. Despite their commonality and prevalence, their cause remains unknown. Theories for the cause of EAMC are primarily based on anecdotal and observational studies rather than sound experimental evidence. Without a clear cause, treatments and prevention strategies for EAMC are often unsuccessful. Evidence Acquisition: A search of Medline (EBSCO), SPORTDiscus, and Silverplatter (CINHAL) was undertaken for journal articles written in English between the years 1955 and 2008. Additional references were collected by a careful analysis of the citations of others’ research and textbooks. Results: Dehydration/electrolyte and neuromuscular causes are the most widely discussed theories for the cause of EAMC; however, strong experimental evidence for either theory is lacking. Conclusions: EAMC are likely due to several factors coalescing to cause EAMC. The variety of treatments and prevention strategies for EAMC are evidence of the uncertainty in their cause. Acute EAMC treatment should focus on moderate static stretching of the affected muscle followed by a proper medical history to determine any predisposing conditions that may have triggered the onset of EAMC. Based on physical findings, prevention programs should be implemented to include fluid and electrolyte balance strategies and/or neuromuscular training.

Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015

The 3rd International Exercise-Associated Hyponatremia (EAH) Consensus Development Conference convened in Carlsbad, California, in February 2015, with a panel of 17 international experts. The delegates represented four countries and nine medical and scientific subspecialties pertaining to athletic training, exercise physiology, sports medicine, water/sodium metabolism and body fluid homoeostasis. The primary goal of the panel was to review the existing data on EAH and update the 2008 Consensus Statement.1 This document serves to replace the 2nd International EAH Consensus Development Conference Statement and launch an educational campaign designed to address the morbidity and mortality associated with a preventable and treatable fluid imbalance . The following statement is a summary of the data synthesised by the 2015 EAH Consensus Panel and represents an evolution of the most current knowledge on EAH. This document will summarise the most current information on the prevalence, aetiology, diagnosis, treatment and prevention of EAH for medical personnel, athletes, athletic trainers and the greater public. The EAH Consensus Panel strove to clearly articulate what we agreed on, did not agree on and did not know, including minority viewpoints that were supported by clinical experience and experimental data. Further updates will be necessary to: (1) remain current with our understanding and (2) critically assess the effectiveness of our present recommendations. Suggestions for future research and educational strategies to reduce the incidence and prevalence of EAH are provided at the end of the document; areas of controversy that remain in this topic have also been outlined. The 3rd International EAH Consensus Development Conference utilised National Institutes of Health guidelines, amended for a more holistic approach to fit the needs of both the group and the topic. Twenty-two individuals (17 accepted) were invited to participate in the consensus conference who: (1) have made scientific and/or clinical contributions to the topic …

Electrolyte and Plasma Changes After Ingestion of Pickle Juice, Water, and a Common Carbohydrate-Electrolyte Solution

CONTEXT Health care professionals advocate that athletes who are susceptible to exercise-associated muscle cramps (EAMCs) should moderately increase their fluid and electrolyte intake by drinking sport drinks. Some clinicians have also claimed drinking small volumes of pickle juice effectively relieves acute EAMCs, often alleviating them within 35 seconds. Others fear ingesting pickle juice will enhance dehydration-induced hypertonicity, thereby prolonging dehydration. OBJECTIVE To determine if ingesting small quantities of pickle juice, a carbohydrate-electrolyte (CHO-e) drink, or water increases plasma electrolytes or other selected plasma variables. DESIGN Crossover study. SETTING Exercise physiology laboratory. PATIENTS OR OTHER PARTICIPANTS Nine euhydrated, healthy men (age = 25 +/- 2 years, height = 179.4 +/- 7.2 cm, mass = 86.3 +/- 15.9 kg) completed the study. INTERVENTION(S) Resting blood samples were collected preingestion (-0.5 minutes); immediately postingestion (0 minutes); and at 1, 5, 10, 15, 20, 25, 30, 45, and 60 minutes postingestion of 1 mL/kg body mass of pickle juice, CHO-e drink, or tap water. MAIN OUTCOME MEASURE(S) Plasma sodium concentration, plasma magnesium concentration, plasma calcium concentration, plasma potassium concentration, plasma osmolality, and changes in plasma volume were analyzed. Urine specific gravity, osmolality, and volume were also measured to characterize hydration status. RESULTS Mean fluid intake was 86.3 +/- 16.7 mL. Plasma sodium concentration, plasma magnesium concentration, plasma calcium concentration, plasma osmolality, and plasma volume did not change during the 60 minutes after ingestion of each fluid (P >or= .05). Water ingestion slightly decreased plasma potassium concentration at 60 minutes (0.21 +/- 0.14 mg/dL [0.21 +/- 0.14 mmol/L]; P <or= .05). CONCLUSIONS At these volumes, ingestion of pickle juice and CHO-e drink did not cause substantial changes in plasma electrolyte concentrations, plasma osmolality, or plasma volume in rested, euhydrated men. Concern that ingesting these volumes of pickle juice might exacerbate an athletes risk of dehydration-induced hypertonicity may be unwarranted. If EAMCs are caused by large electrolyte loss due to sweating, these volumes of pickle juice or CHO-e drink are unlikely to restore any deficit incurred by exercise.

Skinfold Thickness at 8 Common Cryotherapy Sites in Various Athletic Populations.

CONTEXT Researchers have observed slower cooling rates in thigh muscle with greater overlying adipose tissue, suggesting that cryotherapy duration should be based on the adipose thickness of the treatment site. Skinfold data do not exist for other common cryotherapy sites, and no one has reported how those skinfolds might vary because of physical activity level or sex. OBJECTIVE To determine the variability in skinfold thickness among common cryotherapy sites relative to sex and activity level (National Collegiate Athletic Association Division I athletes, recreationally active college athletes). DESIGN Descriptive laboratory study. SETTING Field. PATIENTS OR OTHER PARTICIPANTS Three hundred eighty-nine college students participated; 196 Division I athletes (157 men, 39 women) were recruited during preseason physicals, and 193 recreationally active college athletes (108 men, 85 women) were recruited from physical education classes. INTERVENTION(S) Three skinfold measurements to within 1 mm were taken at 8 sites (inferior angle of the scapula, middle deltoid, ulnar groove, midforearm, midthigh, medial collateral ligament, midcalf, and anterior talofibular ligament [ATF]) using Lange skinfold calipers. MAIN OUTCOME MEASURE(S) Skinfold thickness in millimeters. RESULTS We noted interactions among sex, activity level, and skinfold site. Male athletes had smaller skinfold measurements than female athletes at all sites except the ATF, scapula, and ulnar groove (F₇,₂₇₀₂ = 69.85, P < .001). Skinfold measurements were greater for recreationally active athletes than their Division I counterparts at all sites except the ATF, deltoid, and ulnar groove (F₇,₂₇₀₂ = 30.79, P < .001). Thigh skinfold measurements of recreationally active female athletes were the largest, and their ATF skinfolds were the smallest. CONCLUSIONS Skinfold thickness at common cryotherapy treatment sites varied based on level of physical activity and sex. Therefore, clinicians should measure skinfold thickness to determine an appropriate cryotherapy duration.

Gastric Emptying After Pickle-Juice Ingestion in Rested, Euhydrated Humans

CONTEXT Small volumes of pickle juice (PJ) relieve muscle cramps within 85 seconds of ingestion without significantly affecting plasma variables. This effect may be neurologic rather than metabolic. Understanding PJs gastric emptying would help to strengthen this theory. OBJECTIVE To compare gastric emptying and plasma variables after PJ and deionized water (DIW) ingestion. DESIGN Crossover study. SETTING Laboratory. PATIENTS OR OTHER PARTICIPANTS Ten men (age  =  25.4 ± 0.7 years, height  =  177.1 ± 1.6 cm, mass  =  78.1 ± 3.6 kg). INTERVENTION(S) Rested, euhydrated, and eunatremic participants ingested 7 mL·kg⁻¹ body mass of PJ or DIW on separate days. MAIN OUTCOME MEASURE(S) Gastric volume was measured at 0, 5, 10, 20, and 30 minutes postingestion (using the phenol red dilution technique). Percentage changes in plasma volume and plasma sodium concentration were measured preingestion (-45 minutes) and at 5, 10, 20, and 30 minutes postingestion. RESULTS Initial gastric volume was 624.5 ± 27.4 mL for PJ and 659.5 ± 43.8 mL for DIW (P > .05). Both fluids began to empty within the first 5 minutes (volume emptied: PJ  =  219.2 ± 39.1 mL, DIW  =  305.0 ± 40.5 mL, P < .05). Participants who ingested PJ did not empty further after the first 5 minutes (P > .05), whereas in those who ingested DIW, gastric volume decreased to 111.6 ± 39.9 mL by 30 minutes (P < .05). The DIW group emptied faster than the PJ group between 20 and 30 minutes postingestion (P < .05). Within 5 minutes of PJ ingestion, plasma volume decreased 4.8% ± 1.6%, whereas plasma sodium concentration increased 1.6 ± 0.5 mmol·L⁻¹ (P < .05). Similar changes occurred after DIW ingestion. Calculated plasma sodium content was unchanged for both fluids (P > .05). CONCLUSIONS The initial decrease in gastric volume with both fluids is likely attributable to gastric distension. Failure of the PJ group to empty afterward is likely due to PJs osmolality and acidity. Cardiovascular reflexes resulting from gastric distension are likely responsible for the plasma volume shift and rise in plasma sodium concentration despite nonsignificant changes in plasma sodium content. These data support our theory that PJ does not relieve cramps via a metabolic mechanism.

Cold-Water Immersion for Hyperthermic Humans Wearing American Football Uniforms.

CONTEXT Current treatment recommendations for American football players with exertional heatstroke are to remove clothing and equipment and immerse the body in cold water. It is unknown if wearing a full American football uniform during cold-water immersion (CWI) impairs rectal temperature (Trec) cooling or exacerbates hypothermic afterdrop. OBJECTIVE To determine the time to cool Trec from 39.5°C to 38.0°C while participants wore a full American football uniform or control uniform during CWI and to determine the uniforms effect on Trec recovery postimmersion. DESIGN Crossover study. SETTING Laboratory. PATIENTS OR OTHER PARTICIPANTS A total of 18 hydrated, physically active, unacclimated men (age = 22 ± 3 years, height = 178.8 ± 6.8 cm, mass = 82.3 ± 12.6 kg, body fat = 13% ± 4%, body surface area = 2.0 ± 0.2 m(2)). INTERVENTION(S) Participants wore the control uniform (undergarments, shorts, crew socks, tennis shoes) or full uniform (control plus T-shirt; tennis shoes; jersey; game pants; padding over knees, thighs, and tailbone; helmet; and shoulder pads). They exercised (temperature approximately 40°C, relative humidity approximately 35%) until Trec reached 39.5°C. They removed their T-shirts and shoes and were then immersed in water (approximately 10°C) while wearing each uniform configuration; time to cool Trec to 38.0°C (in minutes) was recorded. We measured Trec (°C) every 5 minutes for 30 minutes after immersion. MAIN OUTCOME MEASURE(S) Time to cool from 39.5°C to 38.0°C and Trec. RESULTS The Trec cooled to 38.0°C in 6.19 ± 2.02 minutes in full uniform and 8.49 ± 4.78 minutes in control uniform (t17 = -2.1, P = .03; effect size = 0.48) corresponding to cooling rates of 0.28°C·min(-1) ± 0.12°C·min(-1) in full uniform and 0.23°C·min(-1) ± 0.11°C·min(-1) in control uniform (t17 = 1.6, P = .07, effect size = 0.44). The Trec postimmersion recovery did not differ between conditions over time (F1,17 = 0.6, P = .59). CONCLUSIONS We speculate that higher skin temperatures before CWI, less shivering, and greater conductive cooling explained the faster cooling in full uniform. Cooling rates were considered ideal when the full uniform was worn during CWI, and wearing the full uniform did not cause a greater postimmersion hypothermic afterdrop. Clinicians may immerse football athletes with hyperthermia wearing a full uniform without concern for negatively affecting body-core cooling.

Golgi tendon organ reflex inhibition following manually applied acute static stretching

Abstract Golgi tendon organ disinhibition may contribute to exercise-associated muscle cramp (henceforth referred to as “cramps”) genesis. Static stretching pre-exercise is prescribed to prevent cramps based on the assumption golgi tendon organ inhibition remains elevated post-stretching. We determined whether stretching increased gastrocnemius golgi tendon organ inhibition and, if so, the time course of this inhibition post-stretching. Twelve participants’ dominant limb medial gastrocnemius inhibition was measured before, and at 1, 5, 10, 15 and 30 min after investigators applied three, 1-min duration stretches. Participants maintained voluntary contraction intensities of 5% of their maximum while the Achilles tendon was stimulated transcutaneously 50 times. Five-hundred millisecond epochs of raw electromyographic activity were band-pass filtered, full-wave rectified and averaged. An algorithm identified inhibitory points and calculated the area, maximum and duration of inhibition. Area of inhibition (F1,14 = 1.5, P = 0.25), maximum inhibition (F1,14 = 0.2, P = 0.72) and duration of inhibition (F1,14 = 1.5, P = 0.24) were unaffected by static stretching over the 30-min post-stretching period. If pre-stretching does prevent fatigue-induced cramping, the mechanism is unlikely to involve the autoinhibition produced by the golgi tendon organ reflex. Further empirical research is needed to validate the proposed link between static stretching and cramping and then to investigate alternative mechanisms.

Initial Electrical Stimulation Frequency and Cramp Threshold Frequency and Force

CONTEXT In the electrically induced cramp model, the tibial nerve is stimulated at an initial frequency of 4 Hz with increases in 2-Hz increments until the flexor hallucis brevis cramps. The frequency at which cramping occurs (ie, threshold frequency [TF]) can vary considerably. A potential limitation is that multiple subthreshold stimulations before TF might induce fatigue, which is operationally defined as a decrease in maximal voluntary isometric contraction (MVIC) force, thereby biasing TF. OBJECTIVE To determine if TF is similar when initially stimulated at 4 Hz or 14 Hz and if MVIC force is different among stimulation frequencies or over time (precramp, 1 minute postcramp, and 5 minutes postcramp). DESIGN Crossover study. SETTING Laboratory. Patients or Other Participants: Twenty participants (13 males: age = 20.6 ± 2.9 years, height = 184.4 ± 5.7 cm, mass = 76.3 ± 7.1 kg; 7 females: age = 20.4 ± 3.5 years, height = 166.6 ± 6.0 cm, mass = 62.4 ± 10.0 kg) who were prone to cramps. INTERVENTION(S) Participants performed 20 practice MVICs. After a 5-minute rest, three 2-second MVICs were recorded and averaged for the precramp measurement. Participants were stimulated at either 4 Hz or 14 Hz, and the frequency was increased in 2-Hz increments from each initial frequency until cramp. The MVIC force was reevaluated at 1 minute and 5 minutes postcramp. MAIN OUTCOME MEASURE(S) The TF and MVIC force. RESULTS Initial stimulation frequency did not affect TF (4 Hz = 16.2 ± 3.8 Hz, 14 Hz = 17.1 ± 5.0 Hz; t(19) = 1.2, P = .24). Two participants had inaccurate TFs when initially stimulated at 14 Hz; they cramped at 10 and 12 Hz in the 4-Hz condition. The MVIC force did not differ between initial frequencies (F(1,19) = 0.9, P = .36) but did differ over time (F(2,38) = 5.1, P = .01). Force was lower at 1 minute postcramp (25.1 ± 10.1 N) than at precramp (28.7 ± 7.8 N; P, .05) but returned to baseline at 5 minutes postcramp (26.7 ± 8.9 N; P > .05). CONCLUSIONS The preferred initial stimulation frequency might be 4 Hz because it did not alter or overestimate TF. The MVIC force was lower at 1 minute postcramp, suggesting the induced cramp rather than the varying electrical frequencies affected force. A 1- to 5-minute rest should be provided postcramp induction if multiple cramps are induced.

Ad Libitum Fluid Intake and Plasma Responses After Pickle Juice, Hypertonic Saline, or Deionized Water Ingestion

CONTEXT Adding sodium (Na(+)) to drinks improves rehydration and ad libitum fluid consumption. Clinicians (∼25%) use pickle juice (PJ) to treat cramping. Scientists warn against PJ ingestion, fearing it will cause rapid plasma volume restoration and thereby decrease thirst and delay rehydration. Advice about drinking PJ has been developed but never tested. OBJECTIVE To determine if drinking small volumes of PJ, hypertonic saline (HS), or deionized water (DIW) affects ad libitum DIW ingestion, plasma variables, or perceptual indicators. DESIGN Crossover study. SETTING Laboratory. PATIENTS OR OTHER PARTICIPANTS Fifteen, euhydrated (urine specific gravity ≤ 1.01) men (age = 22 ± 2 years, height = 178 ± 6 cm, mass = 82.9 ± 8.4 kg). INTERVENTION(S) Participants completed 3 testing days (≥ 72 hours between days). After a 30-minute rest, a blood sample was collected. Participants completed 60 minutes of hard exercise (temperature = 36 ± 2°C, relative humidity = 16 ± 1%). Postexercise, they rested for 30 minutes; had a blood sample collected; rated thirst, fullness, and nausea; and ingested 83 ± 8 mL of PJ, HS, or DIW. They rated drink palatability (100-mm visual analog scale) and were allowed to drink DIW ad libitum for 60 minutes. Blood samples and thirst, fullness, and nausea ratings (100-mm visual analog scales) were collected at 15, 30, 45, and 60 minutes posttreatment drink ingestion. MAIN OUTCOME MEASURE(S) Ad libitum DIW volume, percentage change in plasma volume, plasma osmolality (OSMp,) plasma sodium concentration ([Na(+)]p), and thirst, fullness, nausea, and palatability ratings. RESULTS Participants consumed more DIW ad libitum after HS (708.03 ± 371.03 mL) than after DIW (532.99 ± 337.14 mL, P < .05). Ad libitum DIW ingested after PJ (700.35 ± 366.15 mL) was similar to that after HS and DIW (P > .05). Plasma sodium concentration, OSMp, percentage change in plasma volume, thirst, fullness, and nausea did not differ among treatment drinks over time (P > .05). Deionized water (73 ± 14 mm) was more palatable than HS (17 ± 13 mm) or PJ (26 ± 16 mm, P < .05). CONCLUSIONS The rationale behind advice about drinking PJ is questionable. Participants drank more, not less, after PJ ingestion, and plasma variables and perceptual indicators were similar after PJ and DIW ingestion. Pickle juice did not inhibit short-term rehydration.