Experts have already concluded that exercise can help people with Parkinson's disease improve their motor symptoms, but what is its effect on the cognitive symptoms of this condition?
Besides boosting motor function, exercise could improve memory in people with Parkinson's disease.
Parkinson's disease is a neurological condition that usually stands out for the motor symptoms that it causes, which include tremors, rigidity in the limbs, impaired balance, and a lack of control over movements.
However, this condition also has numerous other symptoms that can leave their mark on a person's quality of life.
Cognitive symptoms, in particular, have been worrying researchers interested in the pathology of Parkinson's disease.
People with this condition experience cognitive impairment, which can worsen in time and eventually evolve into Alzheimer's disease.
When it comes to managing Parkinson's, doctors often advise their patients to take up an exercise regime, since physical activity demonstrably helps improve motor symptoms.
The Parkinson's Foundation call exercise routines "a vital component" of efforts to maintain the quality of life following diagnosis.
But how does physical activity affect other symptoms of Parkinson's disease, particularly cognitive ones?
This is the question that a team of researchers from the German Sport University, in Cologne, the University Medical Center Mainz - both in Germany - and the University of the Sunshine Coast, in Australia, set out to answer by conducting a systematic review of the relevant literature published to date.
Based on the analyzed evidence, the review - which appears in the Journal of Parkinson's Disease - suggests that exercise may have a positive effect across different types of Parkinson's disease symptoms.
Can aerobic exercise really jog memory?
Lead researcher Tim Stuckenschneider notes that he and the team had anticipated these findings, based on the fact that physical activity is associated with cognitive improvements in older adults.
However, there had been no conclusions regarding the relationship between exercise and cognitive symptoms in Parkinson's.
"Physical exercise is generally associated with increased cognitive function in older adults, but the effects in individuals suffering from [Parkinson's disease] are not known," he says.
For the current review, the team searched for relevant randomized controlled trials that had investigated the relationship between Parkinson's, physical activity, and cognition and had been published before March 2018.
All in all, the researchers analyzed data provided by 11 studies. Together, these included information on 508 participants with Parkinson's disease diagnoses and severity scores from one (the lowest) to four (the highest) on the Hoehn and Yahr scale, which measures the degree to which symptoms of the condition have progressed.
Five out of the 11 trials indicated that aerobic exercise, in particular, had a positive impact on memory and executive function, a term referring to the control of behavior, in Parkinson's.
The same studies suggested that combining resistance and coordination exercises also had a positive effect on cognitive function, overall.
Two other trials also found that coordination exercises could improve executive function in people with Parkinson's disease.
'Exercise is medicine'
While the review's results point to a generally positive impact of exercise on cognition in people with Parkinson's disease, the researchers warn that more in-depth studies will be necessary in order to better understand the specifics of this relationship.
Thus, while they were able to conclude that aerobic exercise can improve memory, it remains unclear how specific exercises - such as running versus stationary cycling - affect this cognitive aspect and which type of exercise is likely to bring about the best results.
Moreover, the team notes that the studies included in the present review were not of the best quality and that future research should aim for better-constructed approaches.
Still, Stuckenschneider maintains that "The potential of exercise to improve motor and non-motor symptoms is promising and may help to decelerate disease progression in individuals affected by [Parkinson's disease]."
"As part of a holistic therapy, the potential of exercise to maintain or improve non-motor symptoms such as cognitive function in individuals with [Parkinson's] needs to be acknowledged, and the most effective treatment options need to be defined," he adds.
"This will not only help practitioners to recommend specific exercise programs, but also ultimately improve the quality of life of the individual. Our work shows that 'exercise is medicine' and should routinely be recommended for people with [Parkinson's] to help combat both the physical and cognitive challenges of the disease."