Physical activity, sedentary behavior, and the relationship between gross motor function and passive range of motion in ambulant/semi-ambulant children and adolescents with cerebral palsy

Background

Cerebral palsy (CP) is an umbrella term for permanent disorders caused bydamage to the fetal or infant brain that affect movement, posture, and motorfunction. Although CP is a non-progressive disorder, the degree of physicaldisability may vary as the child grows due to symptoms such as spasticity andsoft tissue contracture. Children and adolescents with CP, like their typicallydeveloped peers, struggle to obtain the recommended degree of daily physicalactivity to help prevent non-communicable diseases (e.g. obesity). Furthermore,levels of sedentary time in children and adolescents with CP are often higher thanrecommended. For these reasons, a key goal for many clinicians working withyoung people with CP is to encourage and facilitate an increase in habitualphysical activity and reduce sedentary time.

In the Nordic countries, the Cerebral Palsy Follow-Up Program (CPUP), which has been adopted as a Danish national clinical quality database, is used by healthcare professionals to offer standardized clinical examinations throughout childhood. Through a multitude of different health- and disease-related variables, the CPUP is designed to support early detection of complications, such as hip dislocation, scoliosis, and muscle contracture, and to improve the quality of healthcare. The passive range of motion of the lower extremities is one example of data registered in the database. The CPUP implemented lower extremity joint passive range of motion thresholds in a traffic light system to identify contractures or restriction of motor function, which can guide clinicians in their decisions regarding intervention, with the potential purpose of improving gross motor
function. However, the thresholds have been questioned as they are based on clinical expertise. Therefore, there is a need to evaluate whether there is an association between range of motion and gross motor function and whether the CPUP thresholds can differentiate between gross motor function scores.

Objective measures of physical activity are not an integrated part of the CPUP. However, physical activity can be evaluated using accelerometers, which is considered a feasible and validated methodology for ambulant/semi-ambulant children and adolescents with CP. Potential predictors of accelerometryassessed physical activity may be identified through the CPUP, allowing for early detection of individuals with low physical activity levels.

Sedentary activities, such as screen time behavior, and their potential association with activities of daily living have not yet been investigated in the population diagnosed with CP. To perform such analyses, screen time behavior can be evaluated by proxy-reported questionnaires that also address quality of life,
overall health, sleep, pain, joint range of motion, and participation in daily activities.

Overall aim

The overall aim of this Ph.D. thesis is to contribute to the evidence on ambulant/semi-ambulant children and adolescents with CP regarding their physical activity, sedentary behavior, and the relationship between gross motor function and joint range of motion. This was accomplished by investigating potential predictors of physical activity, recreational screen time behavior, and the relationship between lower extremity joint range of motion and gross motor function in three studies.

Method

The overall method of this Ph.D. thesis is centered on a prospective clinical cohort. Study I employs prospective prediction using registry data from the CPUP, objective data on physical activity, and proxy-reported outcome measures. Cross-sectional analyses of data from proxy-reported outcome measures and CPUP data were performed in Studies II and III, respectively. A total of 1,459 families with a resident child or adolescent diagnosed with CP aged 8–16 years were invited to participate in the project via secure digital post (“e-Boks”). A total of 446 parents/guardians consented to participate and filled out the proxyreported questionnaires. Data on all children aged 8-16 years (born between 2003 and 2013) with a Gross Motor Function Classification System (GMFCS) level I–III, were retrieved from the CPUP database (n=870).

Study I
This clinical cohort study aimed to investigate potential predictors of habitual physical activity in children and adolescents with CP using objective accelerometer data. Predictive variables were identified in the CPUP database and proxy-reported outcome measures. A modified International Classification of Functioning, Disability, and Health (ICF) model (with the following components: Body Functions and Structures, Activities, Participation, Personal Factors, Environmental Factors, and Quality of Life) was used as a conceptual statistical framework. In total, 123 children and adolescents with valid accelerometer data were included, of which 78 were found in the CPUP database. Sex was identified as a predictor of habitual physical activity, with female sex being associated with lower levels of physical activity. Additional questionnaire data revealed age, popliteal angle, Pediatric Outcomes Data Collection Instrument (PODCI) Sports and Physical Functioning score, and fatigue as predictors of physical activity. Prediction models using all variables from the CPUP database and proxyreported questionnaires predicted 33% and 37% of habitual physical activity, respectively. 

This study demonstrated that data from the CPUP database and a proxy-reported questionnaire can be applied by healthcare professionals to identify children at risk of performing low levels of physical activity. This knowledge may be used to identify children with the greatest need for additional attention with the purpose of increasing physical activity levels.

Study II
This cross-sectional study on data from proxy-reported questionnaires aimed to describe recreational screen time behavior in children and adolescents with CP and to analyze the potential association between screen time behavior and quality of life, participation in recreational physical activities, participation in sports with peers, physical functioning, and sleep duration. A total of 381 children and adolescents were included. A positive association was identified between screen time behavior and age. Negative associations were identified between screen time and sleep time, perceived fatigue, and perceived movement and balance. The results of Study II contribute to the knowledge of recreational screen time behavior in children and adolescents with CP.

Study III
This cross-sectional study aimed to investigate whether measures of range of motion in the lower extremity joints are positively associated with gross motor function in children and adolescents with CP and to investigate whether gross motor function scores differ between categorical (red, yellow, green) range of motion thresholds implemented by the CPUP. In total, 841 children and adolescents were included. Limited associations between passive range of joint motion and gross motor function in children and adolescents with CP were observed. Differences in gross motor function scores were primarily seen between the red and green threshold values, predominantly for the subgroup of children and adolescents with bilateral spastic CP. 

Study III revealed that the relationship between range of motion and gross motor function is complex, and the results supports the importance of including other factors besides range of motion in the decision making regarding possible further interventions for the improvement of gross motor function. 

Conclusion

In conclusion, this Ph.D. thesis identified predictors of physical activity that can be used by healthcare professionals to identify which children and adolescents with CP at GMFSC level I–III are in greater need of increased physical activity. Furthermore, the findings present information about screen time behavior in this population. In addition, the findings highlight the limitations of the present CPUP traffic light system as a tool for clinical decision-making regarding the need for intervention to improve gross motor function. Overall, these findings contribute to the evidence on ambulant/semi-ambulant children and adolescents with CP.