The aim of this study was to explore how to assess and support physical activity of children diagnosed with cancer, and to describe the physical activity levels in children diagnosed with cancer compared to healthy children.

Healthy children’s physical activity was explored with a longitudinal cohort study (study I). The proportion of those who spent less than 1 hour in leisure-time physical activities weekly was 17% at the age of 10-years, 12% at the age of 12-years, and 38% at the age of 15 (n=571). Self-perceived physical competence was positively associated with physical activity (p<0.05), and the association was strengthened with age.

At study II FitbitOne® step counts were compared to ActiGraph with an experimental design in 9-to-10-year old children (n=34). Positive correlations were consistent, r=0.94, but FitbitOne® overestimated the step counts significantly when compared to ActiGraph.

At study III, effectiveness of active video games was studied with randomised controlled trial in 3-to-16-year old children diagnosed with cancer (n=36). The intervention was not effective in physical activity (p=0.63), or motor performance (p=0.77), nor in reducing fatigue (p=1.00). Small sample size and large standard deviations may have hidden the effective results. Physical activity did not differ either by diagnosis or gender. The difference between younger children (aged 3– 8) and older children (aged 9–16) was significant for step counts (p=0.028) and physical activity min/day (p=0.042).

At study IV the physical activity levels (p=0.56) or self-perceived physical competence (p=0.78) did not differ between children diagnosed with cancer and healthy children (data from studies I and III). The promotion of physical activity both in healthy children and in children diagnosed with cancer is warranted.