If an attractive girl touches my arm, I flex a little bit because I think she prefers harder muscles.
如果一个有吸引力的女孩拉着我的胳膊，我会稍微的屈肘，因为我觉得她喜欢坚实的肌肉。
2
Although effort is required to bend a joint or flex a muscle, the body is able to recycle much of the energy expended through spring-like tendons and elegantly arranged muscles.