What adjustments can you do to prevent psoas tightness in an aggresive postion on a road or track bike? I have been paying attention to my own body and I feel that together with a sedentary job and not moving more than with the bike due to the COVID restrictions, I spend a lot of time in that shortened potion of the psoas which I'm sure will yield or aggravate problems around the hip like incontinence due to too much tension.

I have already had a fitting in the bike, measuring the pressure in the saddle, and how my knees and back is positioned.

But what can you do in a roadbike to prevent this issues on long rides in terms of technique while I'm riding? I had always heard about having activated your core, but I think this could also yield to problems because you are over tensing the rectus femoris and then together the psoas, and you don´t really ride relaxed? What muscle should be trainer to counteract this tightness?

I also think stretching is not enough to compensate for such a long sitting + also being in that position on the bike, so there should be something to pay attention while you ride so that al muscles act balanced, but Iḿ not able to find more information than just 5 generic stretches repeated over all websites. 

In general I would like to now how to balance and check that the pelvic floor musculature works as it should during bike riding so that riding keeps being something healthy instead of aggravating being sit for hours.
When they say activate the core, they mean you should also actively use the muscles on the front of your belly and inside. Not just your back. It definitely does not mean you should be overstressing your rectus femoris or psoas.

Something has to hold your posture. Hands do some of the work, but also cannot take too much, because then they become tired and numb. So than the spine and the muscles around it take a lot of stress. Mobilizing the core means taking some of this load from the back muscles.

I recommend this one where the topic is discussed on an actual bike saddle in the other half of the video.


                
            

One has to use the abdominals to held the position, not just leave everything on the back muscles. The context of the video is the pressure on the saddle. But when you watch the pelvis and the lower back when he loosens the abdominals, you can also imagine the stress on the psoas.



There are many articles and videos about core exercise specifically directed to (road) cyclists. For example:


                
            


                
            

Getting those muscles stronger will enable using them for holding the posture and relieve some other parts. If you only look for stretches, it may not be enough for you.