Heat transfer through the head, and cold-induced muscle failure

这项长期研究计划使用基础和应用两种方法，重点研究人类在热/环境应激期间的体温调节、神经肌肉和代谢反应。1)众所周知，冷诱导的体能下降更多地与局部冷有关，而不是与核心冷却有关。我们打算使用经颅磁刺激和电刺激来提供对中枢性疲劳的详细分析，并检验低温将导致中枢性疲劳的假说，包括运动皮质兴奋性降低和皮质内抑制增加。2)虽然人们对肌肉运动中的底物利用已有较多的了解，但在相同代谢强度下，冷诱导的寒战代谢与自愿运动之间的对比分析还很少。我们将比较等代谢颤抖和低强度和高强度代谢率运动条件下的底物利用率。我们假设，与锻炼相比，颤抖更多地依赖于脂肪而不是碳水化合物作为燃料。3)我们还打算确定部分和全部头部浸入冷水中夸大核心冷却效应的机制。一系列研究将确定短期(屏气)和长期(呼吸)头后、面部或两者在冷水中浸泡对心血管和外周血液流动的影响。*我们预计面部浸泡将对周围血液流动和核心冷却产生更大影响。一项验证性研究将确定整个肢体热含量的测量是否可以用作外周血液流动的指标。然后进行长期的身体浸泡，包括背部、面部或整个头部浸泡，同时测量整个肢体的热含量。这将证实浸入头部不同部位对血液流动的影响。最后，一项研究将通过比较躯干上的温水灌流背心和头部上的头罩来测试实际防止冷应激身体核心降温的能力。

This long-term research program focuses on human thermoregulatory, neuromuscular and metabolic responses during thermal/environmental stress, using both basic and applied approaches. 1) It is known that cold-induced decrement in physical performance correlates more with local than core cooling.  We intend to use Transcranial Magnetic Stimulation and electric stimulation to provide a detailed analysis of 'central fatigue' and test the hypothesis that hypothermia will cause central fatigue that includes decreased motor cortical excitability and increased intracortical inhibition. 2) Although much is known about substrate utilization during muscular exercise, comparative analysis between cold-induced shivering metabolism vs voluntary exercise at the same metabolic intensity is lacking. We will compare substrate utilization in iso-metabolic shivering and exercise conditions at low intensity and high intensity metabolic rates. We hypothesize that shivering will rely more on lipids vs carbohydrates for fuel compared to exercise. 3) We also intend to determine mechanisms for exaggerated core cooling effects of partial and total head submersion in cold water.  A series of studies will determine the cardiovascular and peripheral blood flow effects of short term (breath holding) and long-term (breathing) immersion of the back of the head, the face or both, in cold water.  We expect facial immersion to impose a greater effect on peripheral blood flow and core cooling. A validation study will determine if measurements of whole limb heat content can be used as an indicator of peripheral blood flow. Long term body submersions with dorsal, facial or whole head submersions will then be conducted while measuring whole limb heat content. This will allow confirmation of the blood flow effects of submersion of different parts of the head.   4) Finally, a study will test the ability to actually prevent core cooling of a cold-stressed body by comparing effects of warm water-perfusion of a vest on the torso, or of a hood on the head.