Muscle mass alone does not explain fitness drops in Parkinson’s

Older people with Parkinson’s disease who engage in regular exercise tend to perform worse on measures of physical fitness than similarly aged adults without the disease, but these differences are not explained by variations in body muscle mass, a study showed.

While men and women with Parkinson’s tend to have different amounts of muscle and fat, these anatomical differences don’t translate into differences in physical function, the researchers said.

“This finding reinforces the notion that physical function in PD depends on a complex interaction between [neurological], muscular, and postural control factors, beyond the absolute quantity of [muscle] or fat tissue,” they wrote.

An early-access version of the study, “Physical performance and DEXA-derived body composition in adults with Parkinson’s disease participating in a community-based exercise program and community-dwelling older adults: a cross-sectional study,” was published in Scientific Reports.

The study was conducted among adults in Latin America, a region that is underrepresented in Parkinson’s research.

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Parkinson’s disease often leads to problems with mobility and physical function. To help preserve functionality, it’s widely recommended that people with Parkinson’s should stay active and get regular exercise.

The study enrolled 18 adults with Parkinson’s who were regularly participating in community-based exercise programs. These patients underwent a battery of physical function tests and scans to measure the amount of muscle and fat in their bodies.

Researchers found that muscle and fat levels varied significantly by biological sex: Men tended to have more muscle, while women usually had more fat. Despite these differences, male and female patients performed similarly on physical function tests.

“The absence of significant sex differences in physical performance variables suggests that, in this group of individuals with [Parkinson’s disease] participating in a community-based exercise program, structural differences in body composition do not necessarily translate into differential functional performance,” the researchers wrote.

The study also included a control group of adults aged 60 and older without Parkinson’s disease who had low to moderate physical activity levels. On measures of physical function, people with Parkinson’s consistently performed worse than the control group. In particular, Parkinson’s patients walked much more slowly.

“One of the most relevant findings was the marked functional performance impairment in individuals with PD compared with community-dwelling older adults,” the researchers wrote. “The reduction observed in the PD group occurred despite regular participation in [exercise] training, suggesting that physical activity, although beneficial, does not fully compensate for the deficits arising from the neurodegenerative mechanisms inherent to the disease.”

The researchers constructed statistical models to determine whether differences in physical function scores might be explained by variations in muscle mass in people with or without Parkinson’s. The models showed no meaningful association between lean muscle mass and physical function scores.

“This finding may suggest a potential dissociation between muscle structure and physical function in Parkinson’s disease,” the researchers wrote. They said the data suggest that the neurological problems inherent to Parkinson’s have a greater impact on physical function than differences in muscle or fat content.

The researchers noted that the study was limited by its small size, but said the results may help inform which types of exercise and rehabilitation strategies are most beneficial for patients with Parkinson’s.

The findings “support the inclusion of muscle strengthening and functional aerobic conditioning interventions as central components of exercise programs in Parkinson’s disease,” they wrote.

“These findings provide relevant evidence regarding the interaction between Parkinson’s disease, ageing, and physical function in a Latin American context that remains underrepresented in the scientific literature,” they said.