Frustration = Good Workout

I realized something today while doing Jillian Michaels 30 day shred.  I was doing my favorite workout in that dvd, punches, and she said something like "punch out that anger." And then I thought quickly, "that's a good idea."  So I did.  And it felt great.  Instead of thinking "Oh how many more do I have to do?" I just focused on some frustrations I've had.  And boy did that make a difference.  I did it for the rest of the workout and I felt like I could fly.  I don't know how to explain it except that I literally felt that I was punching, jumping, and lifting the frustration right out of me.  I'm going to try to do that every workout and see if it helps.  Let me know if you guys try it and what you think!