Although physical activity has been identified as a relevant determinant of cancer therapy outcome, its valid assessment remains challenging. In principle, direct and indirect assessment instruments can be employed for assessment of physical activity. While direct instruments, e.g. accelerometers, are considered to provide a more objective measurement, indirect tools such as questionnaires are less expensive and more applicable for use in larger study populations. The validity of both forms of measurements in cancer patients is however not well studied. Therefore, this study aims to elucidate the relative validity of an accelerometer in comparison to a standardized physical questionnaire at different time points of cancer therapy. Findings of this study will allow conclusions regarding the ideal modalities for assessment of physical activity in cancer patients.
