I broke my wrist in January and so I was off Cathe for a awhile and then when I started working out again I did some Youtube workouts - pretty much low impact and I wasn't breathing nearly as hard as when I do some of Cathe's workouts. And yet, my heart rate is higher with the lower impact, "easier" workouts I was doing from some of the Youtube programs. I am back doing some of Cathe's workouts that used to be pretty easy for me (today was CTX 10-10-10) and I am huffing and puffing like crazy, but my heart rate is not all that high. Can someone explain to me why this is? I guess I just thought that feeling like I was working so hard - getting out of breath - would be reflected in a higher heart rate.