Morrison Shawnda A, Sleivert Gordon G, Cheung Stephen
Human Performance Laboratory, Faculty of Kinesiology, University of New Brunswick, Fredericton, New Brunswick, Canada.
Med Sci Sports Exerc. 2006 Oct;38(10):1754-61. doi: 10.1249/01.mss.0000230120.83641.98.
To determine the role of aerobic fitness on central neuromuscular activation and maximal voluntary contractile force during hyperthermia.
Thirty-seven healthy males in three distinct groups based on aerobic fitness and training history were passively heated using a liquid conditioning garment in a hot (35 degrees C, 50% RH) environment with the intention of testing neuromuscular function with whole-body hyperthermia. Of these initial participants, 11 of the 13 highly fit (HF; VO2max = 71.2 +/- 5.9 mL x kg(-1) x min(-1), body fat = 5.6 +/- 1.9%), 11 of the 13 moderately fit (MF; 57.2 +/- 4.2 mL x kg(-1) x min(-1), 11 +/- 3.4%), and 4 of the 11 lower-fit (LF; 49.6 +/- 1.1 mL x kg(-1) x min(-1), 19.4 +/- 2.6%) individuals tolerated heating to 39.0 degrees C, with the remainder terminating the experimental protocol early. Maximal force output and voluntary activation were examined during a 10-s maximal isometric knee extension.
Passive heating attenuated force production (-61.7 +/- 69.6 N change from initial values) and decreased voluntary activation (8.6 (12.6), 18.1 (12.4), and 6.1 (3.1)% for HF, MF, and LF training groups, respectively). Cardiovascular strain moderately increased to 60 +/- 14% (P < 0.001), whereas HF and MF had significantly higher MAP than LF at the end of heating (98 +/- 15, 99 +/- 7, and 79 +/- 5 mm Hg for HF, MF, and LF, respectively; P < 0.05). However, the ability to tolerate passive heating to 39.0 degrees C (and above) differed between the HF and MF compared with LF, despite no difference in their psychophysical rankings of thermal sensations and/or (dis)comfort.
Low aerobic fitness and activity level are associated with a decreased tolerance to passive hyperthermia. However, at high body temperatures, maximum force production and voluntary activation were impaired to an equal level regardless of training status.
确定有氧适能在体温过高期间对中枢神经肌肉激活和最大自主收缩力的作用。
根据有氧适能和训练史将37名健康男性分为三个不同组，在炎热（35摄氏度，相对湿度50%）环境中使用液体调节服对他们进行被动加热，目的是通过全身体温过高来测试神经肌肉功能。在这些初始参与者中，13名高适能者（HF；最大摄氧量=71.2±5.9毫升·千克⁻¹·分钟⁻¹，体脂=5.6±1.9%）中的11名、13名中等适能者（MF；57.2±4.2毫升·千克⁻¹·分钟⁻¹，11±3.4%）中的11名以及11名低适能者（LF；49.6±1.1毫升·千克⁻¹·分钟⁻¹，19.4±2.6%）中的4名耐受加热至39.0摄氏度，其余人员提前终止实验方案。在10秒最大等长伸膝过程中检查最大力量输出和自主激活情况。
被动加热减弱了力量产生（与初始值相比变化-61.7±69.6牛），并降低了自主激活（HF、MF和LF训练组分别为8.6（12.6）%、18.1（12.4）%和6.1（3.1）%）。心血管应变适度增加至60±14%（P<0.001），而在加热结束时，HF和MF的平均动脉压显著高于LF（HF、MF和LF分别为98±15、99±7和79±5毫米汞柱；P<0.05）。然而，尽管HF和MF与LF在热感觉和/或（不）舒适的心理物理学评分上没有差异，但HF和MF与LF相比，耐受被动加热至39.0摄氏度（及以上）的能力有所不同。
低有氧适能和活动水平与被动体温过高的耐受性降低有关。然而，在高体温时，无论训练状态如何，最大力量产生和自主激活均受损至相同程度。
