肌肉和人体
骨骼运动发生在人体的关节部位。这种运动是由称为肌肉的片状或条状的 强韧组织拖动而引起的。
肌肉组织有一种特殊的收缩能力，可以带动与之相连的骨骼。 肌 肉在收缩的同时，也会聚成团。 肌肉以条状或片状形式布满全身，存在于皮肤与骨架之间。
骨骼是身体的支架，而肌肉则构成了人的体形。 大多数肌肉接两块骨头，但当肌肉收缩时 只有一块骨头运动。
肌肉与不动骨相连的一端叫肌起端，与动骨相连的一端叫附着端。 有 些肌肉不与骨骼直接相连，而是连着附在骨骼上的不能收缩的带状组织或腱上。 肌肉不能
推动而只能拉动骨骼。 要从肘部弯曲手臂，就要收缩上臂正面的肌肉。 要伸直手臂，背面 的肌肉就得收缩。
这两组肌肉，正面的和背面的，称为相反运动肌肉。 当一组工作时，另 一组就休息。 但有时它们也一起工作。 有时我们要求肌肉不仅仅做简单的单向拖动。
它 们需要转动。 但只有当肌肉与骨骼形成一定角度时，它们才能转动，从而拖动骨骼绕某个 轴旋转。 有几块肌肉的作用较特殊，例如隔膜肌。
它带动肺部吸入空气。 呼吸基本上不 是骨骼运动带动的。
>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.
译路通武汉汉口翻译公司整理
2012.7.17