Recent drug improvement (e.g. abiraterone or enzalutamide) for castration resistant prostate cancer (CRPC) patients has improved survival. As treatment strategies improve and patients live longer, patients must cope with their treatment-induced adverse effects. Improving levels of physical activity (PA) and less amounts of sitting time (e.g. sedentary behavior, SB) could have a positive impact on patient's health, non-cancer mortality, and quality of life and potentially improve survival.

The role of PA has not yet been examined in CRPC patients, which is a clear unmet need. No specific PA guidelines exist for CRPC patients, but specific guidelines are warranted because of advanced disease stage, reduced performance score and comorbidity. It is to be expected that the PA level of CRPC patients is lower compared to non-CRPC patients receiving androgen deprivation therapy (ADT).

This study aims to determine the optimal starting physical therapy prescription in CRPC patients receiving second line hormone treatment.

CRPC patients receiving second-line hormone treatment at Ghent University Hospital are invited to participate in this phase I 3+3 dose escalation design (escalation to next exercise dose per 3 study patients). The prescription start dose is 15min. aerobic training (50-80% maximum heart rate (HRmax). warm-up and cooling-down and 65-80%HRmax. core), 1 set with 8-10 reps. resistance training (50-60% one repetition maximum (1RM), 8 exercises) and 1 set (30s.) with 2 reps. flexibility training (5 exercises). Factors determining compliance for the dose are tolerance and safety. Tolerance for the exercise prescription will be assessed with the Borg scale of perceived exertion after every exercise. Compliant for tolerance is a score ≤16. Safety will be assessed by the visual analogue scale (VAS) (assessed by the patient) for pain and the CTCAE criteria (assessed by a trained health care provider) for bone pain after every exercise. Compliant for safety is ≤3 VAS for exercise-induced pain and \

Inclusion Criteria:

• CRPC patients with second-line hormone treatment
• Able to walk 400 meters without help from another person
• Absence of any psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule (those conditions should be discussed with the patient before registration in the trial)
• ≥4 weeks since any major surgery and fully recovered before patient registration
• Written informed consent must be given according to International conference on harmonization Good Clinical Practice and national regulation.

Exclusion Criteria:

• Musculoskeletal, cardiovascular or neurological comorbidity that prevent the patient to participate in an exercise program
• Painful bone metastases (VAS) at the time of inclusion
• Unstable bone metastases (SINS classification) at time of inclusion