Parkinson's disease (PD) is a neurodegenerative disease that is primarily treated pharmacologically by neurologists. However, there is a growing body of evidence supporting the role of exercise and physical therapy in the treatment of PD but little is known about the potential relationship of medication management and exercise intervention. Furthermore, there is no consensus on the best type of exercise for PD. The majority of people being treated by a physical therapist for mobility deficits will likely be on medications that also aim to help their movement and disability.
In this journal issue, Dibble and colleagues1 explored the effects of 2 different exercise programs, as well as the effects of medication, on several outcome measures related to movement and disability. Their main findings were that (1) both groups improved after intervention, regardless of exercise assignment; (2) exercise and medication together resulted in the largest effect sizes in many outcome measures such as increased muscle force production, Unified Parkinson's Disease Rating Scale motor scores, functional gait assessment, and the 6-minute walk; and (3) strength (force production) changes were observed in the absence of anatomical muscle changes suggesting preserved motor adaptability and neural recruitment in PD.
The study did not have a true control group, as the investigators were interested in identifying whether there were differences between 2 viable exercise alternatives. While one group performed eccentric strength training in addition to the baseline exercise, both groups received comprehensive exercise; for this reason, it may not be surprising that there were no differences between groups. The authors point out that their results agree with a recent meta-analysis, reporting no solid evidence for one type of exercise being more efficacious than another. However, this point remains open for debate because it is well documented that we lack high-quality randomized clinical trials in our field.2 Dibble and colleagues1 should be commended for their rigorous methodology in this study.
Another important finding from the study by Dibble and colleagues1 was that effect sizes were overwhelmingly higher when exercise and medication were combined. These findings remind us that it is critical for physical therapists to be familiar with the important role that dopaminergic medications play in the daily life of a person with PD. It is clear from the study results that even in the pretraining state, the results of our commonly used mobility tests were extremely different when testing was performed in the "on" versus "off" medication state. A clinically important take-home message is that failure to consider the differences in "on" versus "off" testing could significantly impact the ability to measure progress. Furthermore, there may be times when an "off" state assessment could provide valuable information for a physical therapist (assisting with bed mobility at night or determining best assistive device with motor fluctuations). This study highlights the fact that when treating patients with PD, it is important for physical therapists to take into account the medication cycle for the purpose of evaluations, reassessments, and treatments. While the domain of medication management is typically outside of the scope of physical therapist practice, it is important that we are comfortable discussing the patient's PD medications in regard to motoric fluctuations and mobility changes and relay any concerns to the patient's neurologist.
Dibble and colleagues1 used a novel approach for their assessment of quadriceps strength by examining isometric strength and thigh muscle cross-sectional area using magnetic resonance imaging. The authors conclude that changes in force production in the absence of change in cross-sectional area suggest that the improvement may be at the level of neural recruitment. This apparent incongruity is of clinical interesting since while many patients with PD test 5/5 on a quadriceps manual muscle test, but score poorly in more functional tasks such as sit-to-stand transitions. These findings emphasize the need to assess "strength" in a number of ways. It would be interesting to know how the subjects in the study would have performed on a functional test of strength.
A final point to consider is that, as found in this study, quality of life does not consistently improve with exercise, or this may indicate that our available tools are not able to measure a change if there is one. The scale most clinicians use to measure quality of life in people with PD is the PDQ-39. Notably, the total score used in the PDQ-39 includes categories such as social, stigma, and communication that one would not necessarily expect to change after exercise. In fact, in a study we recently published on exercise and PD, we also found that the total PDQ-39 score did not change but when we looked further at relevant subsections, namely activities of daily living and mobility, we found that those categories had higher effect sizes with significant change after exercise when compared with categories we did not expect to change with exercise.3 It would be interesting to know if those subcategories of quality of life changed in the participants involved in this study.
Our field needs high-quality randomized clinical trials to obtain answers to many of our clinical questions. Dibble et al1 did an excellent job of implementing the high standards of a randomized clinical trial to study the complex interaction of exercise, medication, and impairment associated with PD. The detailed description of blinding, data analysis, and the program outline is also helpful to researchers and clinicians who are interested in applying the methods. Although some readers may be tempted to interpret this the findings of study as a negative result (ie, there was no difference between groups), this would be a misguided interpretation; the final message of the study was that some very important outcome measures of functional mobility and strength can improve with either exercise program, performed only 2 times per week for 12 weeks. The findings that both exercise groups improved in many outcome measures, and that the effect sizes were highest when exercise was combined with medication, has important implications for our clinical assessment and treatments of people with PD.
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