Thermoregulatory Responses Of Athletes With A Recent Concussion During A Heat Tolerance Test

Physiological recovery after concussion may continue even after symptoms have resolved. Since thermoregulation relies on the integration of neural pathways, individuals who have had a recent concussion may be at increased risk for heat illness in hot environments. However, it is unknown if concussion alters the neurophysiological pathways governing thermoregulation during heat stress. PURPOSE: To examine thermoregulatory responses of recently concussed athletes during a heat tolerance test. METHODS: Eight athletes (3 female; 16.5 ± 2.8 yr) who had recently incurred a concussion and eight age-, sex- and sport-matched control participants (3 female; 16.5 ± 2.9 yr) walked for 90 min on a motorized treadmill (5 km · hr-1, 2% grade) in an environmental chamber (40 °C, 40% RH). Participants in the concussion group were tested within 30 days of being cleared for full return to activity by a qualified medical professional. Female participants were tested during the follicular phase of their menstrual cycle. Body core temperature (Tc) was measured with an ingestible thermometer pill and heart rate (HR) was monitored with an ECG chest strap. Tc and HR were recorded every 2 minutes. Peak Tc and HR, as well as changes in Tc (ΔTc) and HR (ΔHR) were identified. Group data were compared using t-tests (α = 0.05) and Cohen’s d tests for effect size. RESULTS: Peak Tc was significantly higher in the concussion group than in the control group (38.7 vs. 38.3 °C; P = .033), with a very large effect size (d = 1.04). Likewise, ΔTc was significantly greater in the concussion group than in the control group (1.6 vs. 1.1 °C; P = .020), and this effect size was also very large (d = 1.12). Peak HR and ΔHR were not significantly different between the concussion and control groups (157 vs. 146 bpm; P = .229 and 61 vs. 58 bpm; P = .764, respectively), though the groupwise difference in peak HR had a large effect size (d = 0.62). The ratio of ΔHR:ΔTc was significantly lower in the concussion group compared to the control group (39.9 vs. 58.9 bpm · °C-1; P = .016), with a very large effect size (d = 1.15). CONCLUSION: Athletes with a recent concussion had elevated body core temperatures and attenuated increases in relative heart rate during a heat tolerance test. These alterations are consistent with autonomic dysfunction and may increase an individual's risk for heat illness.