Consortium for Health and Military Performance, Department of Military & Emergency Medicine, F. Edward Hébert School of Medicine, Uniformed Services University, USA; Henry M. Jackson Foundation for the Advancement of Military Medicine, USA.
Consortium for Health and Military Performance, Department of Military & Emergency Medicine, F. Edward Hébert School of Medicine, Uniformed Services University, USA; Henry M. Jackson Foundation for the Advancement of Military Medicine, USA; College of Public Health, Ohio State University, USA.
J Therm Biol. 2020 Apr;89:102563. doi: 10.1016/j.jtherbio.2020.102563. Epub 2020 Mar 2.
This study tested the interactive effects of heat and caffeine on exercise-induced physiological strain by using a 2x2 within-subjects factorial design. Thirty-five physically fit Caucasians underwent a bout of exercise under four conditions wherein ambient conditions (heat vs no heat) and caffeine (placebo vs caffeine; double-blinded) were manipulated. Exercise consisted of a 60-min walk and 5-min step/squat test while wearing weighted backpack. Primary outcomes include measures of physiologic strain (Core temperature [T] and heart rate [HR]). Secondary measures included blood pressure, markers of sweat loss, and creatine kinase (CK). Repeated measures models were created to evaluate the individual and combined effects of heat and caffeine. Key results indicated that heat and caffeine significantly increased T and HR after walking and stair-stepping. No significant heat by caffeine interactions were detected, and caffeine's main effects were relatively low (≤0.17 °C for T and ≤6.6 bpm for HR). Of note, heat and caffeine exhibited opposite effects on blood pressure: caffeine increased both systolic and diastolic blood pressure (by 6-7 mmHg) and heat decreased them (by 4-6 mm Hg; ps < 0.05). In summary, heat and caffeine affected physiologic strain during exercise but exhibited no synergistic effects. In contrast, neither factor affected muscle damage. Clinical implications for heat illness risk in the military are discussed.
本研究采用 2x2 被试内因子设计，测试了热和咖啡因对运动引起的生理应激的交互作用。35 名身体健康的白种人在四种条件下进行了一次运动，其中环境条件（热与不热）和咖啡因（安慰剂与咖啡因；双盲）被控制。运动包括 60 分钟的步行和 5 分钟的台阶/深蹲测试，同时穿着负重背包。主要结果包括生理应激指标（核心温度[T]和心率[HR]）。次要指标包括血压、汗液损失标志物和肌酸激酶（CK）。创建了重复测量模型来评估热和咖啡因的单独和联合作用。主要结果表明，热和咖啡因在步行和爬楼梯后显著增加了 T 和 HR。未检测到热和咖啡因的显著交互作用，咖啡因的主要作用相对较低（T 为≤0.17°C，HR 为≤6.6 bpm）。值得注意的是，热和咖啡因对血压有相反的影响：咖啡因增加了收缩压和舒张压（6-7mmHg），而热降低了血压（4-6mmHg；ps<0.05）。总之，热和咖啡因会影响运动期间的生理应激，但没有协同作用。相反，这两个因素都不会影响肌肉损伤。讨论了热应激对军队热疾病风险的临床意义。
