Where'd that come from?

I've been doing Insanity for a few weeks now, and I can honestly say I'm seeing results. Not only have I become even more energetic (if that is at all possible), but I've also realized bruising on my arms (I don't like tanning, so it's extremely noticeable). Now, with the inclusion of my newest workout, diet and overall fitness changes, I'm a bit confused as to how these bruises are forming, especially when I don't feel them . . . I MUST figure this out, before my arm turns into one giant red bruise.