@sharkbait13 I guess it is a form of interval training more so. I chose the exercises as I thought they would assist more with functionality when I'm older rather than bulking up. Though I am quite muscled/toned from doing them. I don't eat to get big though.
I have this idea about lifting my breathing rate up considerably and then lower back down to benchmark in a reasonably efficient period of time. Same as heart rate etc.
With body temp I also regulate quickly with eating an ice block in the shower. Straight after(I have a chilled shower going into my new bathroom so I can maximize heat and cold shock protein) as I think that is a good thing for my body.
Being able to adapt rather than cruise along for longer period.
So I mixed the exercises as up so there's a bit of a break in between something that is on the high-end of exertion without actually having the rest itself, just working another muscle. Situps and calf raises, leg raise etc are a good rest.
Agree with situps not being very good if you slouch your back or form isn't good. I don't have any issues however as i hold a tight core when doing them and posture is good. I don't know what would be more efficient on the bench for a core exercise.