@astonishingurs
Did you dad get a PSMA, Decipher tests. The 3+4=7 is intermediate risk. It seems that your treatment is very aggressive but the 36 PSA is very high. Was he diagnozed with cancer outside the prostrate? It is hard for us to give suggestions without knowing the number and tests he got.

I would always get second opinions on diagnosis and treatements along with asking for Decipher test (genetic test done on the already taken biopsies to determine a more accurate risk level) and PSMA which shows if cancer has spread outside of prostrate. I also had a bone scan all were negative and Decipher changed my diagnoses from intermediate to low risk.

You mentioned biking. Most of the time a Space/Oar will be done. You cannot bike with the Space/Oar devices in. Also when doing any of the test including PSA it is advisible not to bike at least 72 hours or like mine asked a week prior to test.

Walking is something that is encourage to maintain fitness as well as mental health as will redude stress of treatments. I walked the entire time of my treatments (6 weeks) only having some fatiqure in latter weeks but did not stop my walking.

Talk to his urologist, radiologist/oncologist on these questions as they should be able to advise you. I would suggest also getting a second opinion on diagnosis and treatments.