The goal of this clinical trial is to determine to what extent anticancer immune cells mobilized by aerobic exercise exhibit migratory and functional capacity towards cancer cells in patients undergoing treatment for breast or colorectal cancer. The main questions it aims to answer are: • Do anticancer immune cells mobilized by aerobic exercise will display migratory and functional capacity in patients undergoing treatment for curable breast or colorectal cancer? Hypothesis: exercise will promote cell migration and these cells will display anti-cancer functional characteristics, suggesting a possible adjuvant and immunotherapeutic use of exercise. • Do the magnitude of this anti-cancer immune response to exercise depend on the intensity of exercise? Hypothesis: the achievement of a higher intensity of effort will enable greater mobilization of the cytotoxic lymphocytes of interest, but also the expression of markers predicting a more interesting adjuvant potential to immunotherapy. Researchers will compare the effect of two exercise sessions, one moderate-intensity continuous exercise session (MOD) and one high-intensity interval exercise (HIIE) on the migration and anticancer potentials of mobilized immune cells. Individuals aged between 40 and 70 with curable colon or breast cancer will be recruited to carry out a cross-over study with two experimental conditions. After a preliminary assessment visit, they will take part in: * Two familiarization visits to validate the exercise prescription * Two experimental visits (HIIE and MOD). During these conditions, blood samples will be taken before, after and 1 hour after the end of exercise to collect immune cells in the blood. At the end of the visits, participants will leave with an accelerometer to wear for three days depending on conditions, and a notebook containing a questionnaire to assess fatigue levels over the same three days.