Exercise-associated muscle cramps (EAMCs) are thought to be caused by dehydration and/or electrolyte losses. In this multicenter, cross-sectional study, the authors determined whether sweat rates (SRs), sweat electrolyte concentrations, or sweat electrolyte content differed in athletes with (i.e., crampers) and without (i.e., noncrampers) a history of EAMCs and whether these variables could predict EAMC-prone athletes. Male and female collegiate athletes (N = 350) from 11 sports with (n = 245) and without (n = 105) a self-reported history of EAMCs completed a typical exercise or conditioning session. SRs, calculated from body mass, and posterior forearm sweat were analyzed for sweat sodium concentration ([Na+]sw), sweat potassium concentration ([K+]sw), and sweat chloride concentration ([Cl−]sw). The authors used SRs and sweat electrolyte concentrations to calculate sweat electrolyte content lost. Within each gender, no differences in SRs (204 males, p = .92; 146 females, p = .24); [Na+]sw (191 males, p = .55; 126 females, p = .55); Na+ sw content (191 males, p = .59; 126 females, p = .20); [K+]sw (192 males, p = .57; 126 females, p = .87); K+ sw content (192 males, p = .49; 126 females, p = .03); [Cl−]sw (192 males, p = .94; 77 females, p = .57); and Cl− sw content (192 males, p = .55; 77 females, p = .34) occurred between crampers and noncrampers. Receiver operating characteristic curve analysis revealed that sweat electrolyte content and SRs were predictive of EAMC-prone athletes in American football (area under curve = 0.65–0.72, p ≤ .005), but not in any other sport. EAMCs may not be solely caused by fluid or electrolyte losses in most athletes. Fluid and electrolyte replacement may help American footballers. Clinicians should individualize fluid and electrolyte replacement and understand different etiologies for EAMCs.
Kevin C. Miller, Brendon P. McDermott and Susan W. Yeargin
Susan W. Yeargin, Sean M. Bowman, Lindsey E. Eberman and Jeffrey E. Edwards
During physical activities, youth consume fluids from various delivery methods that may influence hydration behaviors. The purpose of this study was to determine the drinking efficiency of these different methods. Children’s fluid intake was more efficient when drinking from a cup compared with a bottle with no mouth contact and a water fountain, but not compared with a bottle with direct mouth contact. Drinking from the water fountain was the least effective compared with all other methods. Children drink more efficiently when using cups and water bottles with direct mouth contact as the delivery method compared with methods with no mouth contact.
Brendon P. McDermott, Douglas J. Casa, Susan W. Yeargin, Matthew S. Ganio, Lawrence E. Armstrong and Carl M. Maresh
To describe the current scientific evidence of recovery and return to activity following exertional heat stroke (EHS).
Information was collected using MEDLINE and SPORTDiscus databases in English using combinations of key words, exertional heat stroke, recovery, rehabilitation, residual symptoms, heat tolerance, return to activity, and heat illness.
Relevant peer-reviewed, military, and published text materials were reviewed.
Inclusion criteria were based on the article’s coverage of return to activity, residual symptoms, or testing for long-term treatment. Fifty-two out of the original 554 sources met these criteria and were included in data synthesis.
The recovery time following EHS is dependent on numerous factors, and recovery length is individually based and largely dependent on the initial care provided.
Future research should focus on developing a structured return-to-activity strategy following EHS.
Riana R. Pryor, Douglas J. Casa, Susan W. Yeargin and Zachary Y. Kerr
All high schools should implement exertional heat illness (EHI) safety strategies. We determined if there were differences in the implementation of EHI safety strategies between schools with and without additional paid athletic trainers (ATs) or a team physician present at preseason football practices. High schools with multiple ATs or a team physician implemented more EHI prevention and management strategies than schools with only a single AT, including training staff in EHI recognition and treatment and having an emergency action plan. However, schools with a paid team physician were more likely to have double practices in the first week of football practice. Schools with additional medical personnel at football preseason practices were more likely to implement EHI safety strategies.
Zachary Y. Kerr, Susan W. Yeargin, Yuri Hosokawa, Rebecca M. Hirschhorn, Lauren A. Pierpoint and Douglas J. Casa
Context: Recent data on exertional heat illness (EHI) in high school sports are limited yet warranted to identify specific settings with the highest risk of EHI. Objective: To describe the epidemiology of EHI in high school sports during the 2012/2013–2016/2017 academic years. Design: Descriptive epidemiology study. Setting: Aggregate injury and exposure data collected from athletic trainers working in high school sports in the United States. Patients or Other Participants: High school athletes during the 2012/2013–2016/2017 academic years. Intervention: High School Reporting Information Online surveillance system data from the 2012/2013–2016/2017 academic years were analyzed. Main Outcome Measures: EHI counts, rates per 10,000 athlete exposures (AEs), and distributions were examined by sport, event type, and US census region. EHI management strategies provided by athletic trainers were analyzed. Injury rate ratios with 95% confidence intervals (CIs) compared EHI rates. Results: Overall, 300 EHIs were reported for an overall rate of 0.13/10,000 AE (95% CI, 0.11 to 0.14). Of these, 44.3% occurred in American football preseason practices; 20.7% occurred in American football preseason practices with a registered air temperature ≥90°F and ≥1 hour into practice. The EHI rate was higher in American football than all other sports (0.52 vs 0.04/10,000 AE; injury rate ratio = 11.87; 95% CI, 9.22 to 15.27). However, girls’ cross-country had the highest competition EHI rate (1.18/10,000 AE). The EHI rate was higher in the South US census region than all other US census regions (0.23 vs 0.08/10,000 AE; injury rate ratio = 2.96; 95% CI, 2.35 to 3.74). Common EHI management strategies included having medical staff on-site at the onset of EHI (92.7%), removing athlete from play (85.0%), and giving athlete fluids via the mouth (77.7%). Conclusions: American football continues to have the highest overall EHI rate although the high competition EHI rate in girls’ cross-country merits additional examination. Regional differences in EHI incidence, coupled with sport-specific variations in management, may highlight the need for region- and sport-specific EHI prevention guidelines.
Brendon P. McDermott, Douglas J. Casa, Susan W. Yeargin, Matthew S. Ganio, Rebecca M. Lopez and Elizabeth A. Mooradian
Previous field research has not identified sweat rates (SR), fluid consumption (FC), or the efficacy of an educational intervention (EI) for youth during football camp.
To measure hydration status and rehydration performance and examine EI using these data.
Observational with EI randomized comparison.
Thirty-three boys (mean ± SD: 12 ± 2 y, 52.9 ± 13.6 kg, 156 ± 12 cm) volunteered during a 5-d camp with 3 (~2-h) sessions per day (WBGT: 25.6 ± 0.5°C).
Main Outcome Measures:
Hydration status, SR, and FC.
Urine osmolality averaged 796 ± 293 mOsm/L for days 2-5. Game SR (1.30 ± 0.57 L/h) was significantly greater than practice SR (0.65 ± 0.35 L/h; P = .002). Subjects dehydrated during free time but matched fluid losses with FC (0.76 ± 0.29 L/h) during football activities.
Subjects arrived at camp hypohydrated and maintained this condition. They matched FC and SR during, but dehydrated when not playing, football. This may impair recovery and subsequent performance. Hydration EI seemed to have a positive influence on hydration practices.
Stephanie J. Guzzo, Susan W. Yeargin, Jeffery S. Carr, Timothy J. Demchak and Jeffrey E. Edwards
Many athletic trainers use “ice to go” to treat their athletes. However, researchers have reported that icing a working muscle may negate intramuscular (IM) cooling.
The purpose of our study was to determine the length of time needed to cool the gastrocnemius while walking followed by rest.
A randomized crossover study design was used.
Exercise Physiology Laboratory.
Patients or Other Participants:
Nine healthy, physically active males and females (males 5, females 4; age 24.0 ± 2.0 years; height 174.0 ± 8.0 cm; weight 86.3 ± 6.5 kg; skinfold taken at center of gastrocnemius greatest girth, R leg 20.3 ± 4.4 mm, L leg 19.6 ± 4.1 mm) without lower extremity injury or cold allergy volunteered to complete the study.
Participants randomly experienced three treatment conditions on separate days: rest (R), walk for 15 minutes followed by rest (W15R), or walk for 30 minutes followed by rest (W30R). During each treatment, participants wore a 1 kg ice bag secured to their right gastrocnemius muscle. Participants walked at a 4.5km/hr pace on a treadmill during the W15R and W30R trials.
Main Outcome Measures:
A 1 × 3 within groups ANOVA was used to determine the effect of activity on cooling time needed for the gastrocnemius temperature to decrease 6 °C below baseline.
The R condition cooled faster (25.9 ± 5.5 min) than both W15R (33.7 ± 9.3 min; P = .002) and W30R (49.4 ± 8.4 min; P < .001). Average time to decrease 6 °C after W15R was 18.7 ± 9.3 minutes and after W30R was 19.4 ± 8.4 minutes.
Clinicians should instruct their patients to stay and ice or to keep the ice on for an additional 20 minutes after they stop walking and begin to rest.
Stephanie M. Mazerolle, Susan W. Yeargin, Tutita M. Casa and Douglas J. Casa
Edited by Shane Caswell
Matthew S. Ganio, Jennifer F. Klau, Elaine C. Lee, Susan W. Yeargin, Brendon P. McDermott, Maxime Buyckx, Carl M. Maresh and Lawrence E. Armstrong
The purpose of this study was to compare the effects of a carbohydrate-electrolyte plus caffeine, carnitine, taurine, and B vitamins solution (CE+) and a carbohydrate-electrolyte-only solution (CE) vs. a placebo solution (PLA) on cycling performance and maximal voluntary contraction (MVC). In a randomized, double-blind, crossover, repeated-measures design, 14 male cyclists (M ± SD age 27 ± 6 yr, VO2max 60.4 ± 6.8 ml · kg−1 · min−1) cycled for 120 min submaximally (alternating 61% ± 5% and 75% ± 5% VO2max) and then completed a 15-min performance trial (PT). Participants ingested CE+, CE, or PLA before (6 ml/kg) and every 15 min during exercise (3 ml/kg). MVC was measured as a single-leg isometric extension (70° knee flexion) before (pre) and after (post) exercise. Rating of perceived exertion (RPE) was measured throughout. Total work accumulated (KJ) during PT was greater (p < .05) in CE+ (233 ± 34) than PLA (205 ± 52) but not in CE (225 ± 39) vs. PLA. MVC (N) declined (p < .001) from pre to post in PLA (988 ± 213 to 851 ± 191) and CE (970 ± 172 to 870 ± 163) but not in CE+ (953 ± 171 to 904 ± 208). At Minutes 60, 90, 105, and 120 RPE was lower in CE+ (14 ± 2, 14 ± 2, 12 ± 1, 15 ± 2) than in PLA (14 ± 2, 15 ± 2, 14 ± 2, 16 ± 2; p < .001). CE+ resulted in greater total work than PLA. CE+, but not PLA or CE, attenuated pre-to-post MVC declines. Performance increases during CE+ may have been influenced by lower RPE and greater preservation of leg strength during exercise in part as a result of the hypothesized effects of CE+ on the central nervous system and skeletal muscle.
Dawn M. Emerson, Toni M. Torres-McGehee, Susan W. Yeargin, Kyle Dolan and Kelcey K. deWeber
An athletic trainer’s (ATs) role requires current knowledge about factors that can influence hydration status. The purpose of this study was to determine awareness of alcohol and caffeine effects on hydration. Participants were 94 ATs with NCAA Division I or III men’s and/or women’s ice hockey teams and 82 head ATs with professional ice hockey teams. The majority of ATs were correct regarding alcohol’s effects on hydration, specifically knowing alcohol increases urine output (92.1%), delays fluid recovery (81.7%), and dehydrates a euhydrated individual (83.5%). In contrast, fewer ATs were correct that moderate, regular consumption of caffeine does not cause dehydration (20.7%), delay fluid recovery (15.2%), or impair fluid regulatory hormones (9.8%). While ATs were knowledgeable about alcohol effects, there remains misconceptions about caffeine on hydration.