你必须每天锻炼.

you must do exercise everyday.

You have to workout everyday.这里的workout是指“健身，消耗脂肪”的这种锻炼。
You have to exercise everyday.这就是泛指的锻炼。练习。任何联系都可以。联系钢琴，英语，排球。任何事。同样也可以说成“You have to do some exercise everyday.”
同样可以用：You must workout everyday和You must exercise everyday
比较起来：have to较must更为被动。
例如：
I must study hard and make prograss everyday.我必须好好学习，天天向上。（主动的要好好学习）
You have to study hard and make prograss everyday.你要好好学习，才能天天向上。（更象老师或家长的嘱托）
你的句子也要看情况，要看你是不是主动的想练习。