goldenrun - i never check my heart rate either. like the above posters said, i mostly go off how i feel. i make sure i can breath ok. i'm in very good shape as well and ontinue to due advanced workouts. if one day im too tired or cant breathe easy, i take it down a notch or walk in place until i'm ready to pick it back up again. The main thing is to listen to your body. If you feel good and can breathe fine, you shoudl be ok to keep going at the same intensity. if you are gasping for air when normally you dont, its a sign you are doing too much. Im 36 weeks pregnant and im still able to do ab work and lie on my back, even tho i've read you arent supposed to and will feel the negative effects immediately. That doesnt seem to bother me and when it does, i just modify.
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