Blurr wrote:isnt the idea to keep the heart rate up?
As long as you do each back to back then that should be fine but inserting a long pause in between each excercise causes your lactic acid to drop along with your heart rate thus reducing the effectiveness
well i should have explained it more clearly. Yes you cant drop the heart rate if you want to make the exercise effective, i meant roughly do 30 pushups, then 30situps switch to 30 pushups then 30 crunches. but if it isnt effective i must have been doing it wrong for the last 15years.
yes long pauses reduces the amount of carlores burnt hence not making ANY exercise 100% effective, it would just take longer to see any results.
if we really get into follow the warm up i used to get my students to under take:
start by a loose stretch, dont want to put to much tension on any tendions or muscles.
then to get the blood pumping start by a little jog, proceeding into 5 second sprint bursts.
after 5-10min of this we do stretchs. {martial arts, so not evey strecth is important just the ones you work often }
then proceed to do 100 push ups and 10reps with a 2 sec break in between.
after that flip and do 100 situps.
after that flip back and do 20pushups, flip do 20crunches, 20 pushups, 20 situps...and so on and so on. until i stop them.
after that we would do circuit work where they would have to do 15 laps of the room drop and do 20pushups,crunchs, tridips and squats.
then 10laps and repeat the pushups,crunches, tridips and squats, then followed by 5laps to a finsh of once again 20 of each.
by that time i would say the heart rate was up. but then again that was the start of a 2 hour training exercise.
must admit worked for me. And also they are the exercises the institute of sport recommended when i did my teaching accreditation.
using different scales and typo as well had me confused a bit 
105 on one set of scales and 107 on the work scales.
