Aerobic Fitness or Muscle Mass Training to Improve Colorectal Cancer Outcome

Inclusion Criteria: * mCRC with indication for palliative chemotherapy * scheduled for treatment with first-line doublet or triplet chemotherapy, according to the national guideline * able and willing to give written informed consent. Exclusion Criteria: * life expectancy \<6 months * unable to perform basic activities of daily living such as walking or biking * presence of cognitive disorders or severe emotional instability (e.g., Schizophrenia, Alzheimer, alcohol addiction); * presence of other disabling co-morbidities that might hamper physical exercise (e.g. heart failure (NYHA classes 3 and 4), chronic obstructive pulmonary disease (COPD, gold 3 and 4), orthopaedic conditions and neurological disorders (e.g., hernia, paresis, amputation, active rheumatoid arthritis); * insufficient mastery of the Dutch language; * presence of serious cardiovascular or cardiopulmonary conditions (e.g. unstable angina, arrhythmia or valve disease) such that exercise safety is at risk, as judged by the treating physician. * Already participating in structured vigorous aerobic and/or resistance exercise ≥ 2 times per week comparable to our intervention