RESUMEN
The purpose of this study was to compare the maximum potential for heat loss of football linemen (L) and non-linemen (NL) during a National Collegiate Athletic Association (NCAA) summer training camp. It was hypothesized that heat loss potential in L would be lower than NL because of differences in self-generated air flow during position-specific activities. Fourteen NCAA division 1 football players {7 L (mass: 126 ± 6 kg; body surface area [BSA]: 2.51 ± 0.19 m(2)) and 7 NL (mass: 88 ± 13 kg; BSA: 2.09 ± 0.18 m(2))} participated over 6 days in southern Florida (Tdb: 31.2 ± 1.6 °C, T(wb): 27.0 ± 0.7 °C, Tr: 38.4 ± 2.8° C). Simultaneous on-field measurements of self-generated air velocities (v(self)) and mean skin temperatures (Tsk) were performed throughout practice, which included 4 drill categories (special teams, wind sprints, individual drills, and team drills). The resultant net potential for heat loss through convection, radiation, and evaporation (H(total)) was calculated. Values for Tsk were similar between L and NL for all drills (L: 35.4 ± 0.8 °C; NL: 35.4 ± 0.4 °C; p = 0.92). However, v(self) was greater in NL during wind sprints, individual drills, and team drills (p ≤ 0.05). Consequently H(total) was significantly greater in NL for all drills except special teams (p ≤ 0.05). The mean estimated rate of oxygen consumption needed to exceed H(total) was 8.6 ± 1.3 ml · kg(-1) · min(-1) (2.5 ± 0.4 METs) for NL but only 5.6 ± 1.4 ml · kg(-1) · min(-1) (1.6 ± 0.4 METs) for L. A lower heat loss potential occurs in L because of the more static nature of their position-related activities and not because of differences in Tsk. The practical relevance of these findings is that potential interventions that increase convective and evaporative heat loss (i.e., mechanical fans) should specifically target L, particularly while they are participating in static on-field drills and during rest intervals.
Asunto(s)
Regulación de la Temperatura Corporal/fisiología , Fútbol Americano/fisiología , Estaciones del Año , Florida , Sistemas de Información Geográfica , Humanos , Masculino , Consumo de Oxígeno/fisiología , Resistencia Física/fisiología , Temperatura Cutánea , Sudoración/fisiología , Universidades , Adulto JovenRESUMEN
PURPOSE: The study's purpose was to investigate whether differences in local sweat rates on the upper body between American football linemen (L) and backs (B) exist independently of differences in metabolic heat production. METHODS: Twelve NCAA Division I American football players (6 linemen (mass = 141.6 ± 6.5 kg, body surface area (BSA) = 2.67 ± 0.08 m2) and 6 backs (mass = 88.1 ± 13.4 kg, BSA = 2.11 ± 0.19 m2)) cycled at a fixed metabolic heat production per unit BSA of 350 W·m(-2) for 60 min in a climatic chamber (t(db) [dry bulb temperature] = 32.4°C ± 1.0°C, t(wb) [wet bulb temperature] = 26.3°C ± 0.6°C, v [air velocity] = 0.9 ± 0.1 m·s(-1)). Local sweat rates on the head, arm, shoulder, lower back, and chest were measured after 10, 30, and 50 min of exercise. Core temperature, mean skin temperature, and HR were measured throughout exercise. RESULTS: Because metabolic heat production per unit surface area was fixed between participants, the rate of evaporation required for heat balance was similar (L = 261 ± 35 W·m(-2), B = 294 ± 30 W·m(-2), P = 0.11). However, local sweat rates on the head, arm, shoulder, and chest were all significantly greater (P < 0.05) in linemen at all time points, and end-exercise core temperature was significantly greater (P = 0.033) in linemen (38.5°C ± 0.4°C) relative to backs (38.0°C ± 0.2°C) despite a â¼25% lower heat production per unit mass. The change in mean skin temperature from rest was greater in linemen (P < 0.001) after 15, 30, 45, and 60 min, and HR was greater in linemen for the last 30 min of exercise. CONCLUSIONS: Football linemen sweat significantly more on the torso and head than football backs independently of any differences in metabolic heat production per unit BSA and therefore the evaporative requirements for heat balance. Despite greater sweating, linemen demonstrated significantly greater elevations in core temperature suggesting that sweating efficiency (i.e., the proportion of sweat that evaporates) was much lower in linemen.
Asunto(s)
Fútbol Americano/fisiología , Sudoración/fisiología , Termogénesis/fisiología , Superficie Corporal , Temperatura Corporal/fisiología , Cabeza/fisiología , Frecuencia Cardíaca/fisiología , Humanos , Masculino , Consumo de Oxígeno , Temperatura Cutánea/fisiología , Torso/fisiología , Universidades , Adulto JovenRESUMEN
The purpose of this study was to evaluate physical demands of football players during preseason practices in the heat. Furthermore, we sought to compare how physical demands differ between positions and playing status. Male National Collegiate Athletic Association Division 1 football players (n = 49) participated in 9 practice sessions (142 ± 16 minutes per session; wet bulb globe temperature (WBGT) 28.75 ± 2.11°C) over 8 days. Heart rate (HR) and global positioning system data were recorded throughout the entirety of each practice to determine the distance covered (DC), velocity (V), maximal HR (HRmax), and average HR (HRavg). The subjects were divided into 2 groups: linemen (L) (N = 25; age: 22 ± 1 years, weight: 126 ± 16 kg, height: 190 ± 4 cm,) vs. nonlinemen (NL) (N = 24; age: 21 ± 1 years, weight: 91 ± 11 kg, height: 183 ± 8 cm) and starters (S) (N = 17; age: 21 ± 1 years, weight: 118 ± 21 kg, height: 190 ± 7 cm) vs. nonstarters (NS) (N = 32; age: 20 ± 1 years, weight: 105 ± 22 kg, height: 185 ± 7 cm) for statistical analysis. The DC (3,532 ± 943 vs. 2,573 ± 489 m; p = 0.001) and HRmax (201 ± 9 vs. 194 ± 11 b·min(-1); p = 0.025) were significantly greater in NL compared with that in L. In addition, NL spent more time (p < 0.0001) and covered more distance (p = 0.002) at higher velocities than L did. Differences between S vs. NS were observed (p = 0.008, p = 0.031), with S obtaining higher velocities than NS did. Given the demands of their playing positions, NL were required to cover more distance at higher velocities, resulting in a greater HRmax than that of L. Therefore, it appears that L engage in more isometric work than NL do. In addition, the players exposed to similar practice demands provide similar work output during preseason practice sessions regardless of their playing status.