1)But, exercise alone is not enough to counter-balance the damage done by sitting for the majority of our waking hours.

2)Exercising alone can be boring.

老师，为什么第一句用名词exercise，而第二句却使用了动名词Exercising呢？

二句从形式和结构上看，几乎一样呀。是否意味着上面2句可以互换使用名词exercise和动名词Exercising呢？