I've been doing circuit training for about 6 weeks now, I would do 3 circuits and that would just about kill me. So just recently I complete the 3rd circuit and I feel like I have energy and stamina to spare. One thing I've noticed is I even sweat less after the 3rd circuit, but that has me wondering.
Better conditioning has made it easier to do more work, so is my body really burning less calories? I think it would take 4 circuits now to equal the same amount of fatigue that I felt before after 3 circuits, but is my body actually expending less energy to do a given amount of work now??
Yes, your body gets more efficient doing an activity. Aerobic activity will essentially make all the muscles involved stronger and therefore reduce their requirements when performing their duties. For instance your heart will become stronger and so pumping blood requires less energy, lungs etc are the same. It means you'll burn less calories for the same amount of activity.
I'm not sure exactly how much less, I'd hazard a guess that the increased work you're able to do well outweighs the efficiency loss. Also don't forget you'll be doing it quicker so reduced time working will reduce calories too, though there will be an increase in calories burned per unit of time to compensate sightly.
I really wouldn't worry about this stuff. The benefits to exercise are so numerous. Just think about how much longer you'll live and how much better you feel
Wait... what? A stronger muscle burns less calories for the same amount of work? That simply does not make sense. It would make more sense to say that a more efficient muscle would burn less calories, but energy efficiency usually doesn't correlate with strength. Distance runners are highly efficient, does that mean they're very strong?
Also, to suggest that doing the SAME circuit faster than before means that you will burn less calories is akin to saying walking up a hill burns more calories than sprinting up it.
obviously your body is adapting to your workout. Its becoming easier the more you do it. If you up the weights on your circuit it'll be hard again. So if you want to stick with 3 circuits then just up the weight on each exercise and you'll be sweating/huffing and puffing again.
My plan is to reduce my rest between circuits from 3 to 2 minutes and when that gets easier, I'll make the jump to the 4th circuit.
The is the first time I've focused on conditioning that made a noticeable difference, it's a great feeling when basically everything you do that made you out of breath before is suddenly easier and you have something in the tank.