Originally Posted by
bamzi
I have noticed this too.
I suspect it is a result of the gain in body weight reducing one's VO2max.
I am only a novice; I started lifting weights in December 2009 at a skinny 69kg/9% body fat (180cm tall). My resting HR was in the high 30s; my VO2max was 65ml/min (measured with a Polar HR monitor).
7 months later, I am now 83kg/15% body fat. My resting HR is now in the high 40s and my VO2max has dropped down to 53ml/min.
I ride a bike to work and I have noticed that, while my time for the journey has stayed around 18 minutes (despite gaining 14kg of body weight), my time spent above 80% of HR maximum has climbed from 10 or so seconds to 3 or 4 minutes.
So it definitely seems that the extra muscle and fat has had a negative impact on my aerobic capacity.
As an experiment, I aim to cut some body fat once I get my 5x5 squat up to 1.5 x body weight (it's stuck at 1.35 at the moment), and see if I can get my VO2max back up over 60ml/min.
I know it's probably not a concern for those of you who avoid cardio, but if you depend on your cardiovascular system for transport (I don't own a car!) then it can be a bit distressing to see your fitness going south.