肌肉和人體 

骨骼運(yùn)動(dòng)發(fā)生在人體的關(guān)節(jié)部位。這種運(yùn)動(dòng)是由稱為肌肉的片狀或條狀的 強(qiáng)韌組織拖動(dòng)而引起的。

肌肉組織有一種特殊的收縮能力，可以帶動(dòng)與之相連的骨骼。 肌 肉在收縮的同時(shí)，也會(huì)聚成團(tuán)。 肌肉以條狀或片狀形式布滿全身，存在于皮膚與骨架之間。

骨骼是身體的支架，而肌肉則構(gòu)成了人的體形。  大多數(shù)肌肉接兩塊骨頭，但當(dāng)肌肉收縮時(shí) 只有一塊骨頭運(yùn)動(dòng)。

肌肉與不動(dòng)骨相連的一端叫肌起端，與動(dòng)骨相連的一端叫附著端。 有 些肌肉不與骨骼直接相連，而是連著附在骨骼上的不能收縮的帶狀組織或腱上。  肌肉不能

推動(dòng)而只能拉動(dòng)骨骼。  要從肘部彎曲手臂，就要收縮上臂正面的肌肉。  要伸直手臂，背面 的肌肉就得收縮。

這兩組肌肉，正面的和背面的，稱為相反運(yùn)動(dòng)肌肉。  當(dāng)一組工作時(shí)，另 一組就休息。  但有時(shí)它們也一起工作。  有時(shí)我們要求肌肉不僅僅做簡(jiǎn)單的單向拖動(dòng)。

 它 們需要轉(zhuǎn)動(dòng)。  但只有當(dāng)肌肉與骨骼形成一定角度時(shí)，它們才能轉(zhuǎn)動(dòng)，從而拖動(dòng)骨骼繞某個(gè) 軸旋轉(zhuǎn)。  有幾塊肌肉的作用較特殊，例如隔膜肌。

它帶動(dòng)肺部吸入空氣。  呼吸基本上不 是骨骼運(yùn)動(dòng)帶動(dòng)的。

>60 Colds and Age

A critical factor that  plays a part  in susceptibility to colds is age. A

study done by the University of Michigan School of Public Health revealed

particulars that seem to hold true for the general population. Infants  are

the most cold       ridden  group, averaging more than six colds in their first

years. Boys have more colds than girls up to age three. After the age of

three, girls are more susceptible than boys, and teenage girls average

three colds a year to boys' two. The general incidence of colds continues

to decline into maturity. Elderly people who are in good health have as few

as  one or  two colds annually. One exception  is found among  people  in 

their twenties, especially women, who show a rise in cold infections,

because people in this age group are most likely to have young children.

Adults who  delay having children until their  thirties and forties

experience the same sudden increase in cold infections. The study also

found that economics plays an important role. As income increases, the

frequency at which colds are reported in the family decreases. Families

with the lowest income suffer about a third more colds than families at the

upper end. Lower income  generally forces people to live  in more cramped

quarters than those typically occupied by wealthier people, and crowding

increases the opportunities for the cold virus to  travel from person  to

person. Low income  may also adversely  influence diet. The  degree to

which poor nutrition affects susceptibility to colds is not yet clearly

established, but an inadequate diet is suspected of lowering resistance

generally.

譯路通武漢漢口翻譯公司整理

2012.7.17