Our previous work has documented that drivers are thermoregulatory challenged during competitive racing; however, the degree of fluid loss that occurs has not been quantified.
Aim To quantify the degree of fluid losses that occurs during a competitive event under hot (summer) conditions.
Methods Nine male stock car drivers (30 ± 9 yr, 178 ± 3 cm, 83 ± 19 kg) participated in the Pro Series Division of the NASCAR Whelen All-American Series race in August in the Northeastern United States. Seven drivers completed 40 laps with an average speed of ∼73 km/h, totaling ∼18 min in duration. Ambient track temperature was 22.3°C, 90 % rh and average cockpit temperatures were ∼31°C, 61% rh prior to the start of the race, and ∼41°C, 45 % rh upon completion. Sweat rate and percent dehydration was determined via nude body weight (BW) pre- and post-race. Due to race logistics, pre-race BWs were taken approximately one hour before the start of the race, and post-race BWs were taken immediately after the driver exited the car. Urine loss was considered fluid loss, and BWs were corrected for fluid and food intake. Intestinal core (Tc) and skin (Tsk) temperatures, and heart rate (HR) were also assessed.
Results Pre-race BW was 81.5 ± 18.5 kg and decreased to 81.1 ± 18.5 kg immediately post-race (p = 0.001). Average sweat rate was 0.63 ± 0.4 L per hour; as pre-race BWs were taken approximately one hour prior to completion of the race, and this sweat rate incorporated approximately 40 min of pre-race activity which included ∼12 laps ( ∼ 3 min of driving) to establish starting position, 10 min of resting in the vehicle in full uniform, and 30 min of light activity (i.e., making car adjustments), in addition to the race itself. Percent BW loss following the race was 0.77 ± 0.3%. Pre-race Tc was 38.0 ± 0.4°C which increased to 38.5 ± 0.4°C post-race (p = 0.001). Tsk increased from 35.8 ± 0.8°C pre-race to 36.9 ± 0.8°C post-race (p = 0.001) whereas the core-to-skin temperature gradient decreased from a pre-race value of 2.2 ± 0.9°C to 1.6 ± 0.9°C post-race (p = 0.001). HRs post-race were 89 ± 0.0% of the drivers’ age-predicted maximum HR.
Conclusions This is the first study attempting to quantify fluid loss during a competitive stock car race. As this was a short race, sweat rate and% losses in BW were extrapolated to three hours (sweat rate: 1.90 ± 1.2 L per hour; 2.3 ± 1.0% BW loss) and four hours (sweat rate: 2.53 ± 1.5 L per hour; 3.1 ± 1.4% BW loss). As we included 40 minutes of pre-race activity into our sweat rate calculations, the extrapolated sweat rate and% losses in BWs are likely lower than those measured during continuous racing of 3 or 4 hours. These results suggest that fluid losses during competitive racing can be significant. Without a fluid replacement strategy, fluid losses for these drivers may exceed 3% BW and could negatively impact driving performance.
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