Purpose Evidence accumulates that an active lifestyle positively influences cancer treatment outcome. A "smartphone application" (app) such as "RunKeeper," to self-monitor physical activity (PA) might be helpful. This study aimed to examine whether using RunKeeper to increase self-reported PA is feasible in cancer patients and to evaluate patients' opinion about using RunKeeper in a 12-week program.

Methods Adult patients (n = 32), diagnosed with cancer, were randomized between usual care (n = 16) or a 12-week intervention with instructions to self-monitor PAwith RunKeeper (n = 16). Changes in PAwere determined with the Physical Activity Scale for the Elderly (PASE) at baseline (T0), 6 weeks (T1), and 12 weeks (T2). Usability and patients' experiences were tested at T2 with the System Usability Scale (SUS) and a semi-structured interview.

Results Patient mean age was 33.6 years. Between T0 and T1, an increase in PA of 51% (medium estimated effect size r = 0.40) was found in PASE sum score in the intervention group compared with usual care. In addition, total minutes of PA increased with 46% (r = 0.37). These effects decreased over time (T2). Sedentary time decreased with 19% between T0 and T1 and 27% between T0 and T2. Usability was rated Bgood and most patients found RunKeeper use helpful to improve PA.

Conclusions Self-monitoring PA with RunKeeper was safe and feasible in cancer patients. The RunKeeper use resulted in an increase in PA after 6 weeks. RunKeeper usability was rated good and can be used to study PA in cancer patients.