Regular physical activity (PA) has substantial health-related benefits and is associated with improved physical function in people with physical disabilities. Individuals with spinal muscular atrophy (SMA) experience muscle weakness, which results in impaired motor function, mobility, and fatigue. Muscle weakness and fatigue can contribute to a sedentary lifestyle, initiating a cascade of negative health complications and decrease physical activity.
The purpose was (1) to evaluate the ability of the International Physical Activity Questionnaire (IPAQ) to measure PA in SMA and healthy controls (HC), and (2) to determine the relationship of PA to physical function and strength.
Eighteen ambulatory youth and adults with SMA and 16 HC completed the IPAQ to measure PA, as well as a six minute walk test during which fatigue was also measured, timed up and go test and Hammersmith Functional Motor Scale Expanded to measure physical function. Leg strength was assessed by manual muscle testing (MMT) and handheld dynamometry (HHD). Aerobic capacity was assessed using a cardiopulmonary exercise test (CPET) on a recumbent cycle ergometer. Mann-Whitney U Tests were done to determine group differences and Spearman’s rank correlation assessed the relationship between PA and function and strength variables in SMA. Individuals with SMA reported lower total PA (p=0.021) and lower vigorous PA (p=0.002) than HC. There were no group differences in sitting time (p=0.349), walking PA (p=0.189) and moderate PA (p=0.716). There was a moderate inverse correlation between the TUG test and vigorous PA (rs=-.60, p=0.023) and total PA (rs=-.53, p=0.051) in the SMA group. No significant correlations were found in HC.
In SMA, maintaining physical activity may be important to preserve physical function, evaluate the real-life impact of drug treatments, and improve overall health. Novel drug interventions may show improvements during in-clinic testing, but it is unclear how these interventions impact daily activity.