Is it normal for periods to get lighter over time?

I'm 14, this is only my third period. My first was extremely long and heavy (but not painful thank goodness!)- 10 days. Second was heavy and about 7-8 days. This one is light and more brown than red like the first two. I also started being more active this month, with track and all. I was xc runner till November, then I mostly stopped exercising, which is when my first period came. Normal? Will they stay light when I'm active?