Movement in focus: PhD research by Emma den Hartog
25 maart 2026
Children with cancer can experience a significant decline in their physical functioning during illness and treatment. They may lose muscle strength, experience pain and fatigue, or have difficulty walking. PhD candidate Emma den Hartog investigated how often these problems occur and what healthcare professionals can do to improve the physical functioning and quality of life of children with cancer.
Survival rates for childhood cancer continue to improve, but many children develop physical symptoms during their illness and treatment. These include reduced muscle strength and muscle mass, pain (including bone pain), severe fatigue, loss of appetite, and difficulty walking.
Reduced mobility has major consequences for a child’s daily life. Children become less independent and are often less able to take part in everyday activities such as going to school, playing outside, and sports. These ordinary activities are essential for a good quality of life.
At the Prinses Máxima Center, Emma den Hartog studied how physical functioning changes in children with cancer during treatment. She also aimed to better understand which children are at higher risk and how healthcare professionals can recognize problems at an earlier stage. Emma explains: ‘Physiotherapists at the Prinses Máxima Center see that physical functioning declines in children with cancer. With my PhD research, I wanted to gain more insight into this process and explore how we can improve it.’
Movement in ALL
A key part of the research focused on children with acute lymphoblastic leukemia (ALL). Den Hartog found that some children with ALL – some 15% – were already unable to walk at the start of treatment. Another one in four children temporarily stopped walking during the first, intensive phase of treatment. All of these children eventually regained their ability to walk.
Losing the ability to walk is highly distressing for both children and their parents. Emma found that the risk was higher in younger children, in children who lost weight, and in those who spent longer periods in hospital during the first month of treatment.
These findings help prepare children with cancer and their parents for the changes in physical functioning they may experience during treatment. They also enable healthcare professionals to provide support more quickly. In collaboration with physiotherapists, an explanatory video with movement tips for families dealing with ALL was developed. Watch the video below.
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Stem cell transplants and smartwatches
Den Hartog also studied physical functioning in children undergoing stem cell transplantation (SCT). SCT is an intensive treatment with a risk of complications that can temporarily reduce physical functioning. One hundred days after transplantation, children on average had less muscle mass and strength and performed physical tests more slowly than their healthy peers. Children who were fitter before transplantation also showed better physical functioning afterwards.
Next steps
Physiotherapists at the Máxima Center are now starting a follow‑up study to assess the feasibility of a prehabilitation intervention, guided by physiotherapists and dietitians. This may include physical activity adapted to the child’s abilities and a diet enriched with extra protein.
Den Hartog also explored the potential use of a smartwatch. Her research suggests that smartwatches may help measure physical activity, improve understanding of what children can manage at different stages of treatment, and identify problems at an earlier stage. Further research is needed to determine how and for which children a smartwatch can provide the greatest benefit.
Emma den Hartog will defend her PhD thesis on 25 March. She was supervised by Dr. Emma Verwaaijen and Prof. Dr. Wim Tissing of the Prinses Máxima Center, and Prof. Dr. Hanneke van Santen of the Prinses Máxima Center and UMC Utrecht.