Increased cardiovascular demand during strength training

I’ve recently (past month or two) started strength training and have noticed that my heart rate seems higher than normal during threshold and VO2 max efforts. I’m guessing that it may be due to fatigue and possible overtraining, but other metrics look good (HRV, rest, etc). Does the strength training put increased demand on cardiovascular system due to muscle growth? Can anyone point to information on this topic?

How do you feel? I record HRV, but never use that to determine how I feel on a day to day basis, but only when I’m returning from being sick. Listen to your body. If you feel a chronic level of fatigue where you never feel great but are just barely able to make it through workouts, then take a rest week or maybe even two. If you do feel good and it really is just something you are noticing with heart rate, I think it may be do to the fact that you are able to recruit more muscles in exercise. As you strength train, the amount of muscle fibers that you are able to use increases, with this increase mostly being in type 2 fast twitch fibers. My using more of your muscle mass, your body might need to supply more oxygen, which is primarily done by increasing breathing and heart rate. This is just a theory though. Another possible explanation is that you are simply rested after a few months of off/base season. When you are fresh, heart rate tends to go up.

From time to time, lets me know about increasing threshold HR. Whether it is good, bad or indifferent, I don’t know. But I treat it as good thing because it increases also HR cap for Z2 rides (I am calculating HR zones by LTHR).

In general I am feeling good, and mixing in rest days as needed based on fatigue (from various factors). I developed the same theory about having more muscle mass available for recruitment, thus requiring higher HR (until VO2 max increases to compensate?). IANAD so it’s all hand-wavy speculation on my part.

Anyways, I thought it might be a well-understood phenomenon but couldn’t quite even figure out what to use as google search terms…