the trouble with exercise is that it works well only if he or she is interested in it.这句话意思

the trouble with exercise is that it works well only if he or she is interested in it.这句话意思
the trouble with exercise is that it works well only if he or she is interested in it.这句话意思

the trouble with exercise is that it works well only if he or she is interested in it.这句话意思
the trouble with exercise 锻炼的麻烦
is 后有个表语从句,work 起作用,有效果
only if 只有 be interested in 对……感兴趣
译：锻炼的麻烦就是只有当他或她对它感兴趣时才会起很好的作用,有很好的效果.