The combination of hyperthermia, dehydration, and strenuous exercise can result in severe reductions in kidney function leading to an increased risk of developing acute kidney injury (AKI). PURPOSE: We sought to determine if short term heat acclimation (STHA) mitigates the rise in AKI biomarkers during strenuous exercise in heat. METHODS: Twenty men completed two 2-hour bouts of high-intensity interval exercise before (Pre-STHA) and after (Post-STHA) 4 days of 90-120 minutes of exercise in either hot (n=12, 40°C, 40% relative humidity; HEAT) or temperate (n=8, 24°C, 40% relative humidity; CON) conditions. Men drank water ad libitum throughout exercise. Blood was drawn before and after exercise Pre-STHA and Post-STHA. AKI was defined as a serum creatinine increase ≥ 0.3 mg/dL or estimated glomerular filtration rate (eGFR) reduction >25%. RESULTS: HEAT had a similar creatinine increase during exercise Pre-STHA (0.35±0.23 mg/dL) and Post-STHA (0.39±0.20 mg/dL), with creatinine in HEAT increasing more than CON at both time points (0.11±0.07 mg/dL, 0.08±0.06 mg/dL, p≤0.001), respectively. HEAT had a greater reduction in percent change eGFR than CON (p≤0.001) independent of heat acclimation status (Pre-STHA, HEAT: -30.2 ± 9.7%, CON: -10.5 ± 8.5%; Post-STHA, HEAT: -26.4 ± 12.4%, CON: -8.4 ± 5.9%). Biomarkers reached the threshold for AKI in HEAT Pre-STHA (n=9, 75%), with fewer participants reaching the AKI threshold Post-STHA (n=7, 58%, p=0.007). Biomarkers indicated AKI did not occur in CON at either time point. Hydration and body temperatures were similar between HEAT participants with and without biomarkers reaching the threshold of AKI both Pre-STHA and Post-STHA. Change in serum creatinine was related to percent of fluid replaced Pre-STHA (r=0.60, p=0.039), while Post-STHA was related to percent change in plasma volume (r=0.732, p=0.007). CONCLUSION: STHA did not mitigate reductions in eGFR nor increases in serum creatinine during high-intensity exercise in the heat, although the number of participants reaching the threshold for AKI was reduced Post-STHA. This suggests that STHA may reduce the risk of developing AKI during exercise in the heat.
Supported by the National Athletic Trainers’ Association Research and Education Foundation Doctoral Grant 14DGP012.