I've been practicing shotokan karate for 9 years now and loved exercising in general. Due to various reasons, I moved to a different region and started japanese jiu jitsu 5 months ago (there are no karate dojo's around). Since then, because of the current location, I must ride a bike for at least 8 kilometers almost daily (sometimes even more). I know this might not sound like a lot, but before moving, I hadn't even touched a bicycle in years and now it's my main mean of transportation. Couple that with two training sessions a week of jiu jitsu (which I sometimes have to skip for my schedule does not allow me to). After 5 months, I noticed a change in my thigh and calf muscles (a bit thinner and more pronounced, not by much, they were very "pronounced" even before I started cycling).
Regarding the terrain, it's mostly flat but there is an steep overpass over an highway plus a 100 meters region which is pretty steep as well.
Does riding a bicycle for at least 8 kilometers a day (or any substantial number of km for that matter) improve stamina in karate or martial arts in general? Are there any other benefits from it?
The jiu jitsu training (at least from my perspective) teaches a different kind of energy "output" for the feet compared to karate, as in karate matches the legs are continuously under use compared to jiu jitsu (just my observation so far).