Abstract
Despite increasing evidence on exercise in Parkinson’s disease (PD) it remains unclear what type and intensity of exercise are most effective. Currently, most evidence favors moderate- to high-intensity aerobic exercise for its positive effects on motor symptoms as well as disease modifying potential. On the other hand, observational studies have shown that the sheer volume of exercise matters as well, independent of intensity. So far, the efficacy of the volume of exercise has not been confirmed by randomized controlled trials (RCTs). Here, we provide an overview of the ongoing RCTs that promote physical activity in daily life in PD. We found seven RCTs with sample sizes between 30 and 452 and a follow-up between 4 weeks and 12 months. Steps per day is the most commonly reported primary outcome measure. The ongoing RCTs will provide evidence for feasibility, whereafter the PD research field is ready for a next step and to explore the effect of physical activity on disease progression and PD symptoms.
INTRODUCTION
There is increasing evidence and marked interest for non-pharmacological interventions in people with Parkinson’s disease (PD), especially exercise [1]. Moderate- to high-intensity exercise has beneficial effects on motor symptoms [2, 3] with seemingly the most potent effect from high-intensity exercise [2, 4]. Exercise also positively impacts non-motor symptoms such as depression [5, 6] and cognition [7, 8]. Even though clinical trials mostly apply a high-intensity exercise intervention, this type of exercise could be challenging for people with a neurological disease like PD. They may be confronted with multiple barriers due to motor symptoms or non-motor symptoms, such as fatigue and apathy [9]. Different studies also indicate a potential disease-modifying effect from low-intensity exercise or an increase of sheer volume of physical activity. For example, a recent systematic review and meta-analysis shows that low-intensity exercise improves neuroplasticity in patients with neurological disease, including PD, with an equal effect compared to high-intensity exercise [10]. Moreover, observational studies indicate an inverse association between the volume of physical activity and the incidence of PD [11–16] and show that people with PD who are more active, have a slower deterioration of PD symptoms (e.g. gait stability, activities of daily living, and processing speed) [17]. Even reduced mortality rates have been reported, accompanied by a dose-response association, regardless of the intensity [18]. Nonetheless, clinical trials focusing solely on the effect of a higher volume of low-intensity exercise are lacking.
Based on the converging observational evidence, increasing the volume of physical activity in daily life is an interesting approach to explore further. Increasing the volume of physical activities in daily life, such as walking, would be a very accessible option for those who are not able to engage in high-intensity exercise due to impairments or who don’t have access to sport facilities. Here, we aim to review to what extent the existing evidence from observational studies is now being tested further in randomized controlled trials (RCTs). For this purpose, we provide an overview of the ongoing RCTs that promote the volume of physical activities in daily life in PD.
OVERVIEW OF RANDOMIZED CONTROLLED TRIALS OF INTERVENTION PROMOTING PHYSICAL ACTIVITY IN DAILY LIFE
We searched Clinicaltrials.gov for interventional studies in PD with the terms ‘’physical activity” and “Parkinson’s disease”. A study was only included if its status was ‘’not yet recruiting”, ‘’recruiting” or ‘’active, not recruiting”. A study was excluded if it was not a RCT, if a combined intervention was studied, if the intervention consisted of another type of intervention (i.e. medication, a structured exercise intervention or a dietary intervention).
If the people under study did not have Parkinson’s disease, the study was also excluded (Fig. 1). This resulted in the inclusion of 7 studies: Pre-Active PD, STEPS-PD, Amped-PD, MoTIvatE, STEPWISE, KEEP and WHIP-PD. The key elements of the included trials are summarized in Table 1. In the following paragraphs, we will discuss some general characteristics of the studies.

Flowchart. RCT = randomized controlled trial.
Overview of clinical trials on interventions promoting physical activity
Estimated enrolment = number of participants, IPD = Individual Participant Data. N/A = not applicable.
Population
Samples sizes vary between 30 and 452. Four studies include people with PD who are older than 18 years of age, AMPED-PD includes people older than 40 years, STEPS-PD older than 50 years and MoTIvatE includes all ages, including children. Five studies recruit participants with Hoehn and Yahr equal to or less than 3, while disease severity is not specified in two studies. KEEP includes only people with PD with an early diagnosis within 12 months prior to inclusion.
Interventions
All studies deliver an intervention to promote home-based physical activity in daily life, with walking being the most prevalent type of activity. Other studies included activities of the participants’ preference. The degree of supervision varies from active supervised online discussion to an unsupervised, digital intervention. All interventions are home-based, except for WHIP-PD, which is the only study adding in-person in-clinic physiotherapy sessions. Most studies apply different cognitive-behavioral elements such as feedback on performance, self-monitoring and goal setting. KEEP solely focuses on education and AMPED-PD highlights the effect of music on physical activity. The partner is included as motivator in MoTIvatE.
The encouraged frequency of physical activity varies from no specific target frequency to 5 to 7 days per week. Only limited information about the exact details of the interventions is reported in the study registrations. The WHIP-PD study describes the intervention in most detail and for this study, a design article is also available [19].
Primary and secondary outcome measures
Physical activity quantified as steps per day is the most prevalent primary outcome (four studies), and is included as a secondary outcome in the other three studies. Three studies include a primary outcome attempting to assess a measure of the intensity in which these steps are taken. Other primary outcomes include feasibility, compliance, recruitment rate, gait quality and subjective physical activity levels. Five studies report more than one primary outcome. In addition, a variety of secondary outcomes such as gait parameters, quality of life, dual-tasks, balance, system usability, knowledge of exercise, motor symptoms and non-motor symptoms such as depression and cognition are assessed. Information about power and a sample size calculation is only reported by STEPWISE and WHIP-PD.
Follow-up duration
The duration of the interventions varies from 4 weeks to 12 months. Three studies also include follow-up assessments post-intervention varying from 2 weeks to 6 months after termination of the intervention.
Blinding
Four studies are single-blinded and two studies are double-blinded. MoTIvatE is the only unblinded, open-label study.
Compliance
KEEP is the only study reporting compliance as an outcome measure, defined as the percentage of education modules completed.
IPD sharing statement
Individual participant data (IPD) will be shared by one out of seven studies only.
DISCUSSION
We provided an overview of the ongoing RCTs studying promotion of the volume of physical activity in persons with PD. Overall, all studies focus on proving the feasibility (i.e., study whether it is possible to structurally increase the volume of physical activity in people with PD) rather than studying the effectiveness on symptoms, disease progression or disease modifying markers. The nature and design of the RCTs varied. The results of these studies will provide us with essential knowledge on how to shape future studies on the efficacy of increasing the sheer volume of physical activity in people with PD.
A lifestyle change is hard to maintain [20], and these studies will inform us what type of intervention could help people with PD to engage (and keep engaging) in a physically active lifestyle. Digital and remotely delivered interventions will be markedly interesting for its presumably easy accessibility. The WHIP-PD and STEPWISE trials will be interesting in particular, with adequate power and long follow-up. These two studies will provide insights into the feasibility of mHealth delivered support and motivation. Studies on the maintenance of an active lifestyle over a longer period of time are necessary to study effectiveness on PD progression or a potential disease-modifying effect. Three studies in this overview will study the efficacy on Parkinson related symptoms in exploratory analyses. However, these will be evaluated as secondary outcome and not as primary outcome, which may hamper solid conclusions since they are not powered to measure an effect on these outcomes. In the present studies, the effect on putative underlying mechanisms of disease progression such as imaging or biochemical changes are not taken into account. The effect of the sheer volume of physical activity on these biomarkers is unknown, but may be interesting to consider, since higher intensity exercise has shown to induce adaptive cerebral plasticity, as demonstrated using functional and structural magnetic resonance imaging [21]. In addition, moderate-intensity exercise in persons with PD may also alter a variety of blood biomarkers related to inflammation or neuroplasticity [22].
The studies presented here are characterized by several strengths and limitations. Overall, a strength is that all studies include a remote intervention, which is highly relevant because it is easily accessible for large groups of people. In addition, the chosen outcomes assessments are done with validated in-clinic tests or remotely assessed with accelerometers, which are commonly used to evaluate step counts, as a derivative for the volume of physical activity. Outcomes will also be generalizable for an early stage of Parkinson’s disease (i.e. H&Y 3 or less). This is the group of interest who might benefit most from the volume of physical activity and in whom the risk of falling due to increasing activity will be less than those in a further stage. Limitations of these studies are the small sample sizes and the fact that information about power calculations is mostly lacking. In addition, more than half of the included studies have short follow-up periods equal to or less than 10 weeks, which will make it harder to draw conclusions regarding feasibility over a longer period of time. Moreover, only two studies are at least double-blinded, although we are aware that implementing proper blinding in non-pharmacological studies is challenging. Individual participant data (IPD) will be shared by only one out of sevens studies. Despite the heterogeneity of the interventions, data sharing can benefit future studies investigating or incorporating similar ways to promote the volume of physical activity in daily life.
Observational data show an inverse association between the volume of physical activity and the progression of PD symptoms, but clinical trials are still lacking. The insights that will result from the trials currently being performed will not be able to answer effectiveness questions, but will certainly help in designing such clinical trials in the future. Observational data also show that exercise may postpone or even prevent PD [11–16]. An interesting approach besides focusing on people diagnosed with PD, would be to evaluate a putative disease modifying effect of physical activity on the course of disease in a (presumably) prodromal phase. The prevalence of PD is expected to grow exponentially in the coming years [23]. Potential beneficial effects of the volume of physical activity in a prodromal phase could prove to be useful to alter this alarming course.
In conclusion, a variety of interventions promoting the volume of physical activity are currently under study and we look forward to their results. While the benefits of moderate- to high intensity exercise have been established unequivocally, these RCTs mainly focus on feasibility. In the field of moderate to high intensity exercise, we are waiting for the results of the SPARX 3 study [24] (NCT04284436) to address the question of the impact of exercise intensity on the rate of PD progression in early disease. The field of PD deserves and also needs such future trials promoting the volume of physical activity with sufficient power and long follow-up. These studies should evaluate the effect on disease progression markers, such as metabolic changes and imaging, in people in different stages of PD or even consider including people in a prodromal phase. Besides the volume of physical activity, we need more evidence on the effectiveness of the broad spectrum of lifestyle interventions (i.e. nutrition, or stress management) for people with PD. Given the shared complexity and methodological challenges related to studying lifestyle interventions, studies on physical activity may serve as an inspiring example.
DETAILS OF RANDOMIZED CONTROLLED TRIALS OF INTERVENTION PROMOTING PHYSICAL ACTIVITY IN DAILY LIFE
Footnotes
ACKNOWLEDGMENTS
The Center of Expertise for Parkinson & Movement Disorders was supported by a center of excellence grant of the Parkinson’s Foundation. T.H. Oosterhof was financially supported by Asterix / ParkinsonNL Foundation. N.M. de Vries and S. Schootemeijer were financially supported by ZonMw (The Netherlands Organization for Health Research and Development; grant number 91619142 and 546003007).
