Thermoregulatory responses and hydration practices in heat-acclimatized adolescents during preseason high school football.
BACKGROUND
Previous researchers have not investigated the thermoregulatory responses to multiple consecutive days of American football in adolescents.


OBJECTIVE
To examine the thermoregulatory and hydration responses of high school players during formal preseason football practices.


METHODS
Observational study.


METHODS
Players practiced outdoors in late August once per day on days 1 through 5, twice per day on days 6 and 7, and once per day on days 8 through 10. Maximum wet bulb globe temperature averaged 23 +/- 4 degrees C.


METHODS
Twenty-five heat-acclimatized adolescent boys (age = 15 +/- 1 years, height = 180 +/- 8 cm, mass = 81.4 +/- 15.8 kg, body fat = 12 +/- 5%, Tanner stage = 4 +/- 1).


METHODS
We observed participants within and across preseason practices of football. Measures included gastrointestinal temperature (T(GI)), urine osmolality, sweat rate, forearm sweat composition, fluid consumption, testosterone to cortisol ratio, perceptual measures of thirst, perceptual measures of thermal sensation, a modified Environmental Symptoms Questionnaire, and knowledge questionnaires assessing the participants' understanding of heat illnesses and hydration. Results were analyzed for differences across time and were compared between younger (14-15 years, n = 13) and older (16-17 years, n = 12) participants.


RESULTS
Maximum daily T(GI) values remained less than 40 degrees C and were correlated with maximum wet bulb globe temperature (r = 0.59, P = .009). Average urine osmolality indicated that participants generally experienced minimal to moderate hypohydration before (881 +/- 285 mOsmol/kg) and after (856 +/- 259 mOsmol/kg) each practice as a result of replacing approximately two-thirds of their sweat losses during exercise but inadequately rehydrating between practices. Age did not affect most variables; however, sweat rate was lower in younger participants (0.6 +/- 0.2 L/h) than in older participants (0.8 +/- 0.1 L/h) (F(1,18) = 8.774, P = .008).


CONCLUSIONS
Previously heat-acclimatized adolescent boys (T(GI) < 40 degrees C) can safely complete the initial days of preseason football practice in moderate environmental conditions using well-designed practice guidelines. Adolescent boys replaced most sweat lost during practice but remained mildly hypohydrated throughout data collection, indicating inadequate hydration habits when they were not at practice.
Yeargin
Susan Walker
SW
Indiana State University, Terre Haute, IN 47809, USA. susan.yeargin@indstate.edu
Casa
Douglas J
DJ
Judelson
Daniel A
DA
McDermott
Brendon P
BP
Ganio
Matthew S
MS
Lee
Elaine C
EC
Lopez
Rebecca M
RM
Stearns
Rebecca L
RL
Anderson
Jeffrey M
JM
Armstrong
Lawrence E
LE
Kraemer
William J
WJ
Maresh
Carl M
CM
D000064:Acclimatization; D000293:Adolescent; D000704:Analysis of Variance; D001833:Body Temperature Regulation; D016009:Chi-Square Distribution; D003681:Dehydration / Q000209:etiology / Q000503:physiopathology* / Q000517:prevention & control*; D004327:Drinking Behavior; D005538:Football; D006358:Hot Temperature; D006801:Humans; D006854:Hydrocortisone / Q000032:analysis; D008297:Male; D010465:Perception / Q000502:physiology; D010806:Physical Education and Training; D011795:Surveys and Questionnaires; D013546:Sweating / Q000502:physiology; D013739:Testosterone / Q000032:analysis; D013894:Thirst; D014554:Urination / Q000502:physiology
D013739:Testosterone; D006854:Hydrocortisone