Maximum heat loss potential is lower in football linemen during an NCAA summer training camp because of lower self-generated air flow.

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.

Sweating is greater in NCAA football linemen independently of heat production.

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 ∼25% 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.

Large differences in peak oxygen uptake do not independently alter changes in core temperature and sweating during exercise.

The independent influence of peak oxygen uptake (Vo(2 peak)) on changes in thermoregulatory responses during exercise in a neutral climate has not been previously isolated because of complex interactions between Vo(2 peak), metabolic heat production (H(prod)), body mass, and body surface area (BSA). It was hypothesized that Vo(2 peak) does not independently alter changes in core temperature and sweating during exercise. Fourteen males, 7 high (HI) Vo(2 peak): 60.1 ± 4.5 ml·kg⁻¹·min⁻¹; 7 low (LO) Vo(2 peak): 40.3 ± 2.9 ml·kg⁻¹·min⁻¹ matched for body mass (HI: 78.2 ± 6.1 kg; LO: 78.7 ± 7.1 kg) and BSA (HI: 1.97 ± 0.08 m²; LO: 1.94 ± 0.08 m²), cycled for 60-min at 1) a fixed heat production (FHP trial) and 2) a relative exercise intensity of 60% Vo(2 peak) (REL trial) at 24.8 ± 0.6°C, 26 ± 10% RH. In the FHP trial, H(prod) was similar between the HI (542 ± 38 W, 7.0 ± 0.6 W/kg or 275 ± 25 W/m²) and LO (535 ± 39 W, 6.9 ± 0.9 W/kg or 277 ± 29 W/m²) groups, while changes in rectal (T(re): HI: 0.87 ± 0.15°C, LO: 0.87 ± 0.18°C, P = 1.00) and aural canal (T(au): HI: 0.70 ± 0.12°C, LO: 0.74 ± 0.21°C, P = 0.65) temperature, whole-body sweat loss (WBSL) (HI: 434 ± 80 ml, LO: 440 ± 41 ml; P = 0.86), and steady-state local sweating (LSR(back)) (P = 0.40) were all similar despite relative exercise intensity being different (HI: 39.7 ± 4.2%, LO: 57.6 ± 8.0% Vo(2 peak); P = 0.001). At 60% Vo(2 peak), H(prod) was greater in the HI (834 ± 77 W, 10.7 ± 1.3 W/kg or 423 ± 44 W/m²) compared with LO (600 ± 90 W, 7.7 ± 1.4 W/kg or 310 ± 50 W/m²) group (all P < 0.001), as were changes in T(re) (HI: 1.43 ± 0.28°C, LO: 0.89 ± 0.19°C; P = 0.001) and T(au) (HI: 1.11 ± 0.21°C, LO: 0.66 ± 0.14°C; P < 0.001), and WBSL between 0 and 15, 15 and 30, 30 and 45, and 45 and 60 min (all P < 0.01), and LSR(back) (P = 0.02). The absolute esophageal temperature (T(es)) onset for sudomotor activity was ∼0.3°C lower (P < 0.05) in the HI group, but the change in T(es) from preexercise values before sweating onset was similar between groups. Sudomotor thermosensitivity during exercise were similar in both FHP (P = 0.22) and REL (P = 0.77) trials. In conclusion, changes in core temperature and sweating during exercise in a neutral climate are determined by H(prod), mass, and BSA, not Vo(2 peak).

Describing individual variation in local sweating during exercise in a temperate environment.

It has been previously demonstrated that the individual variation in whole-body sweat rate is described by differences in each participant's heat balance status. It was hypothesized that the individual variation in local sweat rate of the forehead (LSR(head)) and forearm (LSR(arm)) would be similarly described using a whole-body heat balance approach, specifically the ratio of evaporation required for heat balance relative to the maximum evaporation possible (i.e. E (req):E (max)). Twelve males cycled at 60% [Formula: see text] for 60 min at 24.9 ± 0.5°C, 31 ± 14% relative humidity. Rectal (T (re)) and aural canal (T (au)) temperatures as well as mean skin temperature ([Formula: see text]), metabolic energy expenditure (M) and rate of external work (W) were measured throughout. In addition, whole-body sweat rate at steady state (WBSR(ss)) was estimated using the change in body mass over the last 15 min of exercise, with LSR(head) and LSR(arm) estimated using technical absorbent patches applied between the 50th and 55th minute. WBSR(ss) significantly correlated with M-W (r = 0.66, P = 0.021), E (req) (r = 0.69, P = 0.013) and E (req):E (max) (r = 0.87, P < 0.001); LSR(head) was significantly correlated with E (req):E (max) (r = 0.82, P = 0.001), but not M-W (r = 0.31, P = 0.328) or E (req) (r = 0.38, P = 0.227); and LSR(arm) significantly correlated with E (req) (r = 0.62, P = 0.031) and E (req):E (max) (r = 0.78, P = 0.003) but not M-W (r = 0.56, P = 0.059). None of WBSR(ss), LSR(head) or LSR(arm) significantly correlated with any variations in T (re), T (au) or [Formula: see text] (i.e. 0.8T (re) + 0.2[Formula: see text]). Secondary analyses also demonstrated that both LSR(head) (r = 0.79, P = 0.002) and LSR(arm) (r = 0.89, P < 0.001) correlated with WBSR(ss). In conclusion, the individual variation in WBSR(ss), LSR(head) and LSR(arm) is described by the ratio of E (req) relative to E (max).