Acclimatization to Heat during Preseason Football Practices at a Division I University: A Pilot Study

A Peer Reviewed Publication of the College of Allied Health & Nursing at Nova Southeastern University Dedicated to allied health professional practice and education http://ijahsp.nova.edu Vol. 7 No. 2 ISSN 1540-580X Acclimatization to Heat during Preseason Football Practices at a Division I University: A Pilot Study Valerie W. Herzog, EdD, LAT, ATC Timothy Ruden, MS Rodney A. Hansen, PhD Molly Smith, PhD David Berry, PhD, LAT, ATC Weber State University United States CITATION: Herzog, V. Ruden, T., Hansen, R., Smith, M., Berry, D. Acclimatization to heat during preseason football practices at a Division I University: A Pilot Study. April 2009, Volume 7 Number 2. ABSTRACT Purpose: The purpose of this study was to examine core temperature (TC) and markers of dehydration during one-a-day (D1) practices compared to two-a-day (D2) practices. Methods: Twenty-five National Collegiate Athletic Association (NCAA) Division I Football Championship Subdivision (FCS) football players volunteered to participate in the study, with thirteen subjects providing data for all four practices. Each subject was measured prior to and following D1 and D2 practices and tested for body mass, core temperature, supine and standing blood pressure, and blood volume changes. Environmental temperature, humidity and barometric pressure were measured at the practice field during the last hour of each practice. Results: During moderate environmental temperatures and humidity, body mass was found to decrease following practice. Core temperature increased following both types of practice. Post practice plasma volume was 4% higher following D1 compared to D2 practice type. Conclusions/Recommendations: In this study, these NCAA Division I FCS football players remained well-hydrated during preseason practice training. The athletes’ plasma volume increased during practice, and even though core temperature increased, it remained lower than levels at which heat illness is indicated. In conclusion, the results of this study indicate that the risk of heat illness in NCAA Division I FCS football players is very low during fall football training practices in conditions of moderate heat and humidity. We recommend that this study should be repeated in various environments, including higher temperatures and/or percent relative humidity where the risk of heat illness may be greater. INTRODUCTION Two-a-day practice sessions are often a part of preseason conditioning in American football (FB). While the extra practice time may help accelerate physical conditioning and assist teams in becoming immediately successful, the physiological stress of participating in repeated two-a-day practices early in preseason places athletes at increased risk of heat injury.1,2 In June 2003, the National Collegiate Athletics Association (NCAA) adopted a new FB preseason practice bylaw (17.11.2) which requires a five-day period to acclimate to equipment and exercise intensity at the start of formal practice and limits the schedule of multiple practices on one day to reduce the risk of injury and heat illness. While the NCAA rule change is based on prudent thermoregulatory adaptation theory, no information regarding its effectiveness in enhancing acclimatization, improving thermoregulatory capacities, and reducing hyperthermic responses are available. Additionally, there are limited studies involving heat stress in FB players during practice.3 Furthermore, studies that have addressed FB clothing and equipment and thermoregulation have been conducted under laboratory conditions and have used © The Internet Journal of Allied Health Sciences and Practice, 2009 Acclimatization to Heat during Preseason Football Practices at a Division I University: A Pilot Study 2 non-FB players as subjects.4-6 For example, McCullough and Kenney reported on thermal insulation and evaporative resistance of FB uniforms using manikins.7 Athletes, whose training begins in the late summer (as is common with preseason football), are more susceptible to developing heat illnesses.8-12 Heat exhaustion in athletes can quickly progress to life-threatening exertional heat stroke due to multi-system organ failure.13 Increased metabolic heat production, coupled with environmental conditions, exceeds the body’s ability to dissipate heat, thereby increasing the athletes’ core temperature.14 Therefore, an understanding about how preseason FB practices influence the development of exertional heat-related illness can assist sports medicine professionals in preventing, recognizing, and promptly treating these conditions. Traditional emergency assessment of an athlete’s core temperature requires insertion of a rectal thermometer. However, the use of ingestible temperature sensors allows sports medicine professional to monitor, recognize, and promptly treat athletes participating in sports, and prevent the development of heat-related illnesses such as heat exhaustion and heat stroke. Other than rectal temperature, gastrointestinal core temperatures, measured with ingestible temperature sensors, have been shown to be the only alternative measurement that accurately assesses core body temperature.15,16 The purpose of this study was to examine core temperature (TC) and markers of dehydration during one-a-day (D1) practices compared to two-a-day (D2) practices. METHODS Subjects Twenty-five National Collegiate Athletic Association (NCAA) Division I Football Championship Subdivision (FCS) football players volunteered to participate in the study (age = 20.5 ± 1.8 years; height = 187.2 ± 8.3 cm; body mass = 102.7 ± 18.4 kg; body mass index = 29.1 ± 3.7 kg @ m-2; supine resting systolic and diastolic blood pressure = 122.3 ± 8.3 and 71.2 ± 9.1 mm Hg, respectively.) The study was approved by the University’s Institutional Review Board of Human Subjects, and all subjects signed an informed consent form prior to participation. Thirteen of the twenty-five subjects provided data for all four practices. Research Design This observational, repeated measures design study used pre- and post-practice measurements to compare thermoregulation during D1 (one practice per day) and D2 (two-practices per day) practices (Table 1). Both practice types were measured during the first and second weeks of the official preseason practice period during the month of August. Practices took place at an elevation of approximately 4,700 feet. During practice, the athletes were allowed unrestricted access to cold water and were given no instructions regarding water consumption. Table 1. A single group repeated measures 2 x 2 x 2 ANOVA (Practice Type x Practice Number x Practice Time) was used to determine the effects of practice type (single day practice and double day practice) on core temp, body mass , plasma volume, cell volume, and blood volume. (Table shown to clarify data collection) D1 D2 P1 P2 P1 P2 Pre P Pos P Pre P Pos P Pre P Pos P Pre P Pos P Athlete 1 2 3 4 5 6 7 8 9 10 11 12 13 Practice Time Means Pr (...truncated)