<mylife>
I have started to row primarily for health benefits. My job and my hobbies require me to sit for my whole life. The only time when I don't sit is... when I sleep basically. Therefore, although my blood test is fine, I always feel tired and sleepy, I have poor sleep, etc. This impacts my daily motivation and even my social abilities.
It's funny to see doing sport at first is making feel you worse. So I do understand why a lot of people tend to stop working out as after 2-3 trainings, the body is really full of lactate, sore muscles and hurt by reactive oxygen species. On top of that, most of rookies tend to train between zone 3 and 4 (working at threshold, not sure of this is the right English term, i.e. at the limit of aerobic and anaerobic), which is the most demanding for the body and may bring injury quickly (very common for rookie runners).
I used to cycle a lot but always badly: once per week and too fast, for too long. I was always feeling bad after, never hungry etc. I guess it is obvious for many people that sitting 6 days per week and going for a 3 hours workout on a road bike isn't a good idea, even if you do this for months/years. I needed a new sport in my life allowing to perform nearly every day without the pain of wearing special clothes, braving cars traffic in town, braving seasons (winter and fall especially) etc. I already rowed in a previous life in a club and I was enjoying, so... I bought a rower. And now it's hard to brake and tell myself I need a day of rest.
I only started for a few weeks and already feel the energy raising along with better nights of sleep. I make sure to start easy as I am a beginner, so zone 2 only which is around 2:40/500m for me.
</mylife>
Well, end of context, here is my question (at last!)

I was wondering if zone 2 training, known for its great abilities to improve mitochondrial function, can be used with any sport and have the benefits for the whole body, whatever the muscles in "use".
I mean, if I cycle in zone 2 for 2 hours, will this help as much as rowing for 2 hours at the same heart rate?
The heart will always be used so I guess there's no difference for it. However, cycling will mostly use legs while rowing will also use the arms+chest.
In the end will chest+arms muscles' mitochondria improve even if I cycle? Or are mitochondria improving only for the targeted muscles?
Cheers