Physical inactivity and secondary health complications in cerebral palsy: Chicken or egg?

“Nobody really lives long enough to die of old age. We die from accidents, and most of all, disuse.”

-Walter Bortz II, M.D.

In conjunction with the primary neurologic insult, individuals with cerebral palsy (CP) are at risk for various secondary health complications including orthopedic abnormalities, exaggerated sedentary lifestyles, lower fitness, and musculoskeletal fragility. Fundamental movement skills are thought to be a central predictor of activity participation among children with CP, with those who are more proficient tending to be more physically active.¹ However, more than one third of ambulatory children are at risk for losing the ability to walk by early adulthood.² Clinical efforts are thus largely directed at preserving ambulatory status by treating the overt symptoms of CP such as pain, fatigue, gait and orthopedic abnormalities, and spasticity. Despite the documented efficacy of these interventions to alleviate symptoms of physiologic or biomechanical dysfunction, what remains to be determined is whether such practices actually lead to sustainable behavior modifications and/or preservation of activity patterns throughout the lifespan. In reality, and even with the typically-developing pediatric population, low physical activity participation has become a public health burden, with less than 25% of adolescents meeting recommended levels.³ Given that habitual activity behaviors are known to track from adolescence into adulthood,⁴ and moreover, that physical inactivity is a modifiable risk factor for various cardiometabolic diseases, cancer and early all-cause mortality, evaluating the prevalence and contributing factors of participation among youth of all abilities may help to inform viable public health interventions.

In their recent study, Mitchell and colleagues,⁵ sought to determine the extent to which personal and environmental factors contribute to habitual physical activity among ambulatory children and adolescents with CP. Their findings identified several factors that were associated with greater objectively-measured physical activity, including physical “capacity” (as determined by the 6-minute walk test [6MWT]), lower age, the male gender, and greater participation in the home and community. This is a valuable addition to the body of literature, and should serve as yet another reminder for clinicians and parents to vigilantly monitor physical activity patterns among children with CP. Perhaps more importantly, it also highlights several modifiable factors which could be targeted to potentially improve activity participation. Yet, as with all cross-sectional research, the interpretation of these findings must be viewed within the context of an unknown direction of causation. The authors make a strong and valid case for examining factors that could be associated with variability in physical activity participation. Many would argue, on the other hand, that physical activity is also a modifiable behavior, and that a general tendency or motivation to participate in more activity might be a driver of greater overall participation in other activities in the home and community. Moreover, among children and adolescents that are engaged in greater volumes of physical activity, a natural physiologic adaptive-response would be enhancement of muscular endurance, and consequently, better performance in the 6MWT. Whether lower functional capacity and lack of home/community participation “causes” insufficient habitual physical activity, or if the modifiable behavior of physical inactivity, itself, is the contributing factor leading to progressive declines in physical capacity and less participation in other aspects of life (i.e., reverse causality), is an interesting and complex topic.

Regardless, and as the authors accurately point out in the introduction, there has been very little focus on better understanding modifiable factors that reinforce healthy behaviors in CP. There is also a paucity of links between the basic research on etiologic factors and medical treatments for CP, and the translational research on preventive health strategies unique to this population. By comparison with the general typically-developing population, the study of health-related physical activity and exercise in CP is in its infancy. Indeed, nearly 60% of all papers on this topic have been published in the last five years alone. Future, longitudinal research is thus urgently needed to identify optimal strategies that reduce barriers and reinforce greater participation in habitual, health-related physical activity in this population. Such efforts will be vital for changing the current paradigm towards prioritizing the support of cardiometabolic health, musculoskeletal integrity, motor function preservation, and quality of life for persons with CP throughout the lifespan.