The purpose of this investigation was to evaluate the thermal load resulting from wearing football helmets. Traditionally, football helmet studies have focused on their efficacy in protection from head trauma without considering the potential injury related to thermal stress. Eight collegiate males performed three trials wearing athletic shorts, shirt and either one of two different helmets or no helmet while running on a treadmill (exercise-5 mph/30 minutes; recovery- 3 mph/5 minutes). The environmental temperature of the thermal chamber was 30°C and 85% relative humidity. During the trials, rate of perceived exertion (RPE), heart rate, core temperature (rectal, tympanic) and physiological strain index (PSI) were measured every 5 minutes. Weight loss was assessed from pre to post nude body weights. No statistical differences were observed for comparison among helmet trials or no helmet trial for heart rate, RPE, core temperatures, weight loss, or PSI. All of these physiological variables increased over time through the work and recovery phases of the treadmill exercise, demonstrating a significant thermal load resulting from metabolic heat production due to exercise and environmental conditions. These results suggest that the helmet alone does not provide a significant impairment to heat loss. One should not discount the possibility of other helmet designs or the accumulative effects of helmet and football gear in creating a serious thermal challenge. Sponsored by Kenny Howard Athletic Training Fellowship-Hughston Sportsmedicine Foundation and Department of Health and Human Performance at Auburn University
We sought to determine if a pre-workout supplement (PWS), containing multiple ingredients thought to enhance blood flow, increases hyperemia associated with resistance training compared to placebo (PBO). Given the potential interaction with training loads/time-under-tension, we evaluated the hyperemic response at two different loads to failure.Thirty males participated in this double-blinded study. At visit 1, participants were randomly assigned to consume PWS (Reckless™) or PBO (maltodextrin and glycine) and performed four sets of leg extensions to failure at 30% or 80% of their 1-RM 45-min thereafter. 1-wk. later (visit 2), participants consumed the same supplement as before, but exercised at the alternate load. Heart rate (HR), blood pressure (BP), femoral artery blood flow, and plasma nitrate/nitrite (NOx) were assessed at baseline (BL), 45-min post-PWS/PBO consumption (PRE), and 5-min following the last set of leg extensions (POST). Vastus lateralis near infrared spectroscopy (NIRS) was employed during leg extension exercise. Repeated measures ANOVAs were performed with time, supplement, and load as independent variables and Bonferroni correction applied for multiple post-hoc comparisons. Data are reported as mean ± SD.With the 30% training load compared to 80%, significantly more repetitions were performed (p < 0.05), but there was no difference in total volume load (p > 0.05). NIRS derived minimum oxygenated hemoglobin (O2Hb) was lower in the 80% load condition compared to 30% for all rest intervals between sets of exercise (p < 0.0167). HR and BP did not vary as a function of supplement or load. Femoral artery blood flow at POST was higher independent of exercise load and treatment. However, a time*supplement*load interaction was observed revealing greater femoral artery blood flow with PWS compared to PBO at POST in the 80% (+56.8%; p = 0.006) but not 30% load condition (+12.7%; p = 0.476). Plasma NOx was ~3-fold higher with PWS compared to PBO at PRE and POST (p < 0.001).Compared to PBO, the PWS consumed herein augmented hyperemia following multiple sets to failure at 80% of 1-RM, but not 30%. This specificity may be a product of interaction with local perturbations (e.g., reduced tissue oxygenation levels [minimum O2Hb] in the 80% load condition) and/or muscle fiber recruitment.
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