Armstrong D W
National Naval Medical Center, Naval Medical Research Institute, Bethesda, MD, USA. dwarmstrong@bth12:med.navy.mil
Med Sci Sports Exerc. 1998 Jun;30(6):880-4. doi: 10.1097/00005768-199806000-00016.
The purpose of this study was to measure resting metabolic rate, plasma norepinephrine, and plasma immunoreactive beta endorphin during exposures to cold air during two consecutive 5-d periods, separated by 2 weekend days, in two groups of women differing in aerobic fitness.
Plasma norepinephrine (NE), plasma immunoreactive beta-endorphin (IBE), and resting metabolic response (RMR) were measured during repeated exposures to 3.5 degrees C air in two groups of women differing in aerobic fitness. Ten women, separated into highly fit (HFW) and less fit (LFW) groups, sat in 22 degrees C air for 45 min followed by 45 min in 3.5 degrees C air each day during two consecutive 5-d periods separated by two weekend days.
Norepinephrine was not different between groups during warm air exposure; however, following 45 min of cold air, NE was two times higher in HFW compared with that in LFW (P < 0.001). Plasma IBE was elevated (P < 0.02) in HFW compared with that in LFW but was not affected by exposure to cold on any test day. Warm RMR was not different between groups and remained unchanged during the study period. Cold RMR was significantly higher in LFW compared with that in HFW (P < 0.01). Resting metabolic rate peaked at 30% of VO2peak in LFW by the 5th minute of cold exposure on day 1 before declining to 21% and remaining steady. In contrast, RMR in HFW peaked at about 13% and then fell to 9.4% before slowly increasing to 14% by the end of 45 min. On other test days HFW RMR increased to 14% of VO2peak and rose slowly through 45 min of cold exposure while LFW RMR peaked at 24% of VO2peak before declining to 20% and remaining steady.
Our findings suggest that, in women, aerobic fitness alters the endocrine and metabolic responses to acute cold air exposure. The norepinephrine response is exaggerated in highly fit women exposed to cold but not the metabolic response. Immunoreactive beta endorphin was not affected by exposure to cold but was elevated in highly fit women. We further conclude that the temperature threshold for acclimation to cold air by women may be higher than the air temperature used in this study.
本研究的目的是在两组有氧适能不同的女性中，测量她们在两个连续的5天时间段内暴露于冷空气期间的静息代谢率、血浆去甲肾上腺素和血浆免疫反应性β-内啡肽，两个时间段之间间隔2个周末日。
在两组有氧适能不同的女性重复暴露于3.5摄氏度空气期间，测量她们的血浆去甲肾上腺素（NE）、血浆免疫反应性β-内啡肽（IBE）和静息代谢反应（RMR）。将10名女性分为高适能组（HFW）和低适能组（LFW），在两个连续的5天时间段内，她们每天先在22摄氏度空气中坐45分钟，然后在3.5摄氏度空气中坐45分钟，两个时间段之间间隔两个周末日。
在暖空气暴露期间，两组之间的去甲肾上腺素没有差异；然而，在冷空气暴露45分钟后，HFW组的NE比LFW组高两倍（P<0.001）。与LFW组相比，HFW组的血浆IBE升高（P<0.02），但在任何测试日都不受冷空气暴露的影响。暖空气时的RMR在两组之间没有差异，并且在研究期间保持不变。LFW组的冷RMR显著高于HFW组（P<0.01）。在第1天冷空气暴露的第5分钟，LFW组的静息代谢率在VO2峰值的30%时达到峰值，然后下降到21%并保持稳定。相比之下，HFW组的RMR在约13%时达到峰值，然后下降到9.4%，在45分钟结束时缓慢上升到14%。在其他测试日，HFW组的RMR增加到VO2峰值的14%，并在45分钟的冷空气暴露期间缓慢上升，而LFW组的RMR在VO2峰值的24%时达到峰值，然后下降到20%并保持稳定。
我们的研究结果表明，在女性中，有氧适能会改变对急性冷空气暴露的内分泌和代谢反应。在暴露于寒冷的高适能女性中，去甲肾上腺素反应会增强，但代谢反应不会。免疫反应性β-内啡肽不受冷空气暴露的影响，但在高适能女性中升高。我们进一步得出结论，女性适应冷空气的温度阈值可能高于本研究中使用的气温。
