Thermal Responses in Football and Cross-Country Athletes During Their Respective Practices in a Hot Environment

Abstract

OBJECTIVE: To determine if football (FB) players and cross-country (CC) runners had different thermal responses to their respective training sessions. DESIGN AND SETTING: On days 4 and 8 of preseason training, we assessed core (T(c)) and skin (T(sk)) temperatures. SUBJECTS: Fifteen collegiate athletes volunteered: 10 FB players (age = 21.2 +/- 1.14 years, height = 193.5 +/- 4.8 cm, mass = 116.6 +/- 16.3 kg, and V(2max) = 44.7 +/- 9.4 mLkg(-1)min(-1)) and 5 CC runners (age = 22.8 +/- 2.77 years, height = 176.3 +/- 8.9 cm, mass = 71.16 +/- 8.9 kg, and V(2max) = 71.3 +/- 6.18 mLkg(-1)min(-1)). MEASUREMENTS: We measured T(c) using ingestible sensors before, during, and immediately after exercise. The T(sk) was measured at the calf, forearm, back, chest, and forehead sites. Level of dehydration was assessed by urine specific gravity. RESULTS: Mean wet-bulb temperature was 74 degrees F (23.33 degrees C). Resting T(c) in shorts and T-shirts was higher in the FB group. The T(c) midway through practices and runs was higher in the CC and FB subjects when active, compared with the FB subjects when inactive. Postexercise T(c) was higher in the CC group than the FB group with pads, and postconditioning T(c) was higher in the FB subjects with pads versus no pads. Forehead, chest, back, and mean weighted T(sk) were higher in the FB group. The T(c) and urine specific gravity were not correlated. CONCLUSIONS: The T(c) fluctuated in the FB subjects during practice depending on exercise intensity, whereas T(c) increased steadily in the CC subjects during continuous running. Thus, CC athletes may have to decrease intensity to maintain thermoregulation. Our FB players seemed to dissipate heat adequately during rest periods.

Figure 1

Heat stress risk temperature and humidity graph. Environmental conditions above ▪ = no pads, between ▪ and ▴ = half pads and below ▴ = full pads. Stars indicate morning temperature and humidity when football players were wearing helmets, shoulder pads, and shorts. Diamonds indicate afternoon temperature and humidity when football players were wearing full pads. Figure adapted with permission, from Kulka TJ, Kenney WL. Heat balance limits in football uniforms. Physician Sportsmed. 2002;30(7):29–39.

Figure 2

Core body temperature in football players and cross-country runners at rest and during practice. *Significantly different from cross-country. †Significantly different from football mid inactivity. All P < .05.

Figure 3

Core body temperature in football players immediately after conditioning with pads on versus pads off. *Significantly different from pads off; P < .05.

Figure 4

Core temperature in football players and cross-country runners on day 4 versus day 8. *Significantly different from day 4; P < .05.

Figure 5

Skin temperature in football players and cross-country runners during both morning (am) and afternoon (pm) practices. *Significantly different from cross-country runners; P < .05.

Figure 6

Core body temperature and urine specific gravity in football players and cross-country runners; r = −.17; P = .13.