Effect of High Intensity Interval Training on Mechanisms of Neuroplasticity in Parkinson's Disease Patients

There are experimental evidences of the important role of high intensity physical exercise in Parkinson's disease (PD) treatment, that induces similar effects to pharmacotherapy. So far, the mechanisms of the impact of these changes on the brain subcortical and cortical regions functioning, motor activities and cognitive functions are still not clear.

The aim of this longitudinal (prospective) human experiment is to examine the effects of two cycles of 12-weeks high-intensity interval training (HIIT) on: (i) the level of dopamine (DA) in putamen in striatum, (ii) neurophysiological function of subcortical and cortical motor structures and skeletal muscle activity, (iii) psychomotor behaviors critically associated with dopamine dependent neural structures functioning and (iv) neurotrophic factors' secretion level in blood.

The investigators will recruit 40 PD individuals, who will be divided into two groups: one of them will perform two 12-weeks cycles of HIIT (PD-TR), and the other will not be trained (PD-NTR) with HIIT. The investigators will also recruit 20 age-matched healthy controls (H-CO) as additional control group who will not perform the HIIT. The PD-TR group will perform the two 12-weeks cycles of the HIIT, that induces beneficial, neuroplastic changes and alleviates the PD symptoms, what was found in earlier studies. All PD subjects (PD-TR and PD-NTR) will be examined during their medication "OFF-phase" (it means after dopaminergic drugs withdrawal) before (Pre) and after (Post) training cycles (first training cycle - HIIT 1; second training cycle - HIIT 2), and namely: Pre HIIT 1, 1 week-, 1.5 month- and 3 months-Post HIIT 1; and then similarly 1 week-, 1.5 month- and 3 months-Post HIIT 2. The subject from H-CO will be tested only once.

To examine the assumed HIIT-induced changes in brain functioning the investigators will apply: (i) the positron emission tomography (PET), (ii) the functional magnetic resonance imaging (fMRI), (iii) electroencephalography (EEG) and (iv) an analysis of neurotrophic factors secretion level in blood. The investigators will also assess motor and non-motor symptoms of PD and psychomotor behaviors based on neuropsychological tests of cognitive functions and manual dexterity.

The results of this project will help to answer the fundamental questions about HIIT induced mechanisms of neuroplasticity in PD patients, what is important from scientific and treatment-strategy point of view.

I. Research Project Objectives

Aim 1. To examine the effect of two HIIT cycles on presynaptic striatal DA availability (in dorsal putamen) in the tested PD patients using PET imaging method with the 18F-dopa - \[18F\]fluorodopa uptake, which provides in this case a very good index of restored striatal presynaptic dopaminergic function (Brooks and Pavese, 2011).

Hypothesis 1. The presynaptic striatal dopaminergic function will improve (18F-dopa uptake increase) after the first and second bout of HIIT cycle compared to baseline in the PD-TR group, and will sustain in 1 year follow up time frame (3 months after the second HIIT cycle cessation). In the PD-NTR group, the presynaptic striatal dopaminergic function will not improve or even will be worsened (18F-dopa uptake decrease) in the same time interval. Importantly for this hypothesis the annual decrease of putaminal 18F-dopa is about 10% in early PD (Morrish et al., 1995).

Aim 2. To characterize an influence of two HIIT cycles on neurophysiological functions (NPFs) of: (i) motor and cognitive subcortical and cortical structures, (that are critically dependant on the presynaptic DA availability), using fMRI and EEG, and (ii) skeletal muscles engaged in motor task, using surface EMG. The following neurophysiological functions of central nervous system (CNS) will be tested during performance of the DA availability-dependant self initiated index finger motor task and during mental imagery of this motor task (cognitive task): (i) a level of activation of subcortical and cortical structures, and (ii) strength of functional coupling (functional connectivity) between neural structures. For skeletal muscles NPFs', the investigators will study a strategy of motor units activation. Also, since the investigators will record EEG and EMG simultaneously, the investigators will assess strength of cortico-muscular coupling.

Hypothesis 2. NPFs will improve after the first and second bout of HIIT cycle compared to baseline in the PD-TR group, and will sustain in 1 year follow up time frame. Namely, the investigators speculate that for the motor task and mental imagery task in CNS activity, it will be: (1) an increase of activation in substantia nigra (SN), putamen (PUT), primary motor cortex (M1), supplementary motor area (SMA); (2) decrease of activation of lateral premotor cortex (PMC) and cerebellum; with simultaneous (3) increase of functional coupling of: SN with PUT; PUT with M1, PMC, SMA and dorsolateral prefrontal cortex (DLPFC); and DLPFC with M1, PMC, SMA and cerebellum; (4) decrease of functional coupling between M1, PMC, SMA, cerebellum and parietal cortex; and (5) for the mental imagery task the investigators additionally assume an increase of parietal and decrease of occipital cortex activation. For the skeletal muscle function it will be an improvement in recruitment strategy of motor units. Taking into the data from the simultaneous recording of electrical activity of brain cortex and skeletal muscles engaged in motor tasks, the investigators assume strengthening of corticomuscular coupling. In the PD-NTR group NPFs will not improve or even will be worsened in the same time interval and especially after the 1 year from the baseline.

Aim 3. To characterize an influence of two HIIT cycles on the psychomotor behaviors (PMBs), critically dependant on the DA availability and brain's NPFs. The following PMBs will be tested during several experiments: (1) self initiated bimanual anti-phase index finger flexion/extension movement task and mental imagery of this task during the fMRI scans, (2) self initiated bimanual anti-phase index finger abduction/adduction movement task and mental imagery of this task during the simultaneous EEG, EMG and force recordings; (3) simple functional test of bimanual dexterity (using peg board test), (4) all motor and non-motor PD symptoms evaluation, based on neurological assessment, (5) overall cognitive function and specifically aspects of executive function using psychological tests.

Hypothesis 3. PMBs will improve after the first and second bout of HIIT cycle compared to baseline in the PD-TR group, and will sustain in 1 year follow up time frame, as a consequence of the improvements of presynaptic striatal DA availability and NPFs, The PMBs improvement will not be present in the PD-NTR group, or even the PMBs will be worsened in the same time interval and especially after the 1 year from the baseline.

Aim 4. To evaluate: (i) the effect of two HIIT cycles on BDNF (brain-derived neurotrophic factor), NGF (nerve growth factor), IGF-1 (insulin like growth factor type 1) secretion level in blood treated as markers of neuroplasticity efficiency and (ii) an influence of BDNF polymorphism on PD patients neuroplastic responsiveness to HIIT (expressed in exercise-induced increase of presynaptic DA level, and improvement of NPF' and PMBs).

Hypothesis 4. The secretion level of the BDNF, NGF and IGF-1 will increase after the first and second bout of HIIT cycle compared to baseline in the PD-TR group, and will sustain in 1 year follow up time frame. In contrary to PD-TR group, the improvement in BDNF, NGF and IGF-1 secretion level will not be present in the PD-NTR group or even their level will decrease after 1 year follow up. The PD patients neuroplastic responsiveness to HIIT will be influenced by the BDNF polymorphism type, with potentially worse responsiveness for the Val66Met polymorphism of BDNF (this polymorphism causes a valine to methionine change at position 66 of the proBDNF protein).

Aim 5. To investigate the relationships of presynaptic DA availability with the NPFs, PMBs and BDNF level of specific polymorphism type.

Hypothesis 5. The investigators hypothesize that, the HIIT related increase of presynaptic DA availability will be significantly positively correlated with: (i) an improvement of NPFs and PMBs, and with an increased level of BDNF secretion in blood, and (ii) negatively with the BDNF Val66Met polymorphism type in PD-TR group. Contrary to the above, there will be lack or less significant correlations of presynaptic striatal DA availability with NPFs, PMBs and BDNF level in the PD-NTR group.

II. Research design and work plan

This project is a longitudinal, 1-year follow up randomized controlled study with 3 arms. Whole block type randomization process is carried out by the investigators of this study using sequentially numbered sealed envelopes. Opaque envelopes are used to conceal allocation. The project enrolls two PD patients' groups: PD-TR - the PD patients who will perform physical training cycle; PD-NTR - non-trained PD patients and one H-CO - healthy control group that will not perform the HIIT cycles. All PD subjects (PD-TR and PD-NTR) will be examined during their medication "OFF-phase" in the following time points: Pre HIIT 1, 1 week-, 1.5 month- and 3 months-Post HIIT 1; and then similarly 1 week-, 1.5 month- and 3 months-Post HIIT 2. The subject from H-CO will be tested only once.

III. Research methodology

III.1.1. Subjects characteristics The 40 PD individuals (aged 45-65 years), are qualified to the study after being diagnosed to have an idiopathic PD, based on neurological assessment. The diagnosis of Parkinson's disease are based on medical history, physical and neurological examinations and response to L-dopa. Patients are clinically assessed with the UPDRS and the H\&Y scale by experienced movement disorder neurologist. To obtain the most homogeneous group of patients with unified type of medication (important for PET measurements), that will be able to perform HIIT cycle and participate fully in the testing sessions, the investigators limit patients' recruitment to mild PD (1-2 points in H\&Y scale) with prevalence of bradykinesia and absence or less accentuated tremor. The healthy control group will comprise of age-, gender, height- and body mass-matched healthy individuals.

III.1.2. Subjects recruitment The PD subjects are recruited from Neurology Clinics in Warsaw, Poland. The healthy elderly control group of subjects are recruited based on: (i) public advertisement and (ii) contacts with the Universities of the Third Age and the Seniors' Clubs around the Warsaw city.

III.2. Training procedures The patients from PD-TR group will perform two 12-week HIIT cycles divided with 3 months of break. This HIIT cycle will consist of three 1-hour training sessions weekly. Each 1-hour training session will consist of 10-minutes warm-up (at slow voluntary speed), 40-minutes of interval exercise and 10-minutes cool-down phase. In each training session, the interval exercise part will consist of 10 sets of 4 minutes interval including 2-minutes cycling at ≥ 60 \[rpm\], but preferably at 80-90 \[rpm\] (fast phase of interval) and 2-minutes cycling at ≤ 60 \[rpm\] (slow phase of interval). The training will be performed on a stationary cycle ergometer (MONARK, Ergomedic 874E, Sweden), that allows to measure cadence \[rpm\]) and power \[W\]. The heart rate (HR, \[bpm\]) will be measured by Polar system (Polar, Finland). Training supervisor will adjust the resistance for each patient to ensure cycling at each patient's target heart rate (THR) and with appropriate speed. All training sessions will be performed while the patients' medication on-phase (beneficial effect of anti-parkinsonian medication). The patients will pedal on the cycloergometer at 60%-80% of their individualized HRmax and will be encouraged to cycle faster (80-90 rpm, or 30% faster than their preferred voluntary speed) during the fast phase of the interval training. Each patient will increased his/her target heart rate every 2 weeks by 5% from 60% up to 80% in the following order: 60% of the HRmax during the first two weeks, 65% during the 3-4 week, 70% during 5-6 week, 75% during 7-9 week and 80% during 10-12 week of training period. During each part of these 36 training sessions (warm up; fast and slow phase of interval training part; slow down), for each subject, the investigators will measure: (i) the values of the % of HRmax, (ii) cadence and power, and (iii) patients' perception of exercise intensity using the Borg Rating of Perceived Exertion (RPE) (Borg, 1982). To enhance the cognitive engagement in exercised PD patients the cadence (cycling speed) data will be presented on each patient's screen using custom-made feedback system. The patient will see two vertical bars, on which the first is going to be the set target level of speed (appropriate for the slow or fast phase of interval) and the second is going to be the an actual speed generated by exercising patient. Additionally, the PD patients will be cued with metronome and verbal comments of instructor to pedal with appropriate rhythm which will be adjusted to the set speed.

IV. Statistical analysis

The investigators will first perform a between-group comparison for all demographics and clinical characteristics to check for baseline differences (Student's t test or Mann-Whitney U tests for normally and non-normally distributed data or the Fisher's exact test for contingency data). Repeated measures ANOVA will be used to perform a between-group comparison of changes in the testing points. Significant main effects will then be subjected to a post-hoc pair-wise comparison primarily between PD-TR and PD-NTR, and PD-TR and H-CO. Correlation analysis (Pearson or Spearman correlation coefficient) will be performed between PET data (showing DA availability), and fMRI, EEG, EMG (describing NPFs), PMBs, and neuroplasticity markers outcomes. For all analyses, a significance level will be set to α=0.05 with Bonferroni adjustments for multiple comparisons when necessary.

Eligibility Criteria:
Inclusion Criteria:

* for PD patients: age 45-65 years-old; diagnosis of idiopathic PD; and modified Hoehn and Yahr stages between 1.5 and 3
* for healthy controls: age-matched to PD patients, lack of neurological disorders
* all participants will also satisfy the following eligibility criteria: (i) proficient in Polish; (ii) no significant cognitive impairments (dementia), as assessed by the MMSE test (Folstein et al., 1975) score ≥ 27; (iii) no prior history of neurological, psychiatric, or other disorders that may influence CNS structure and function; (iv) no current medication to affect cognitive psychomotor functioning (opioid analgesics, anxiolytics or antidepressants) and (v) signed informed consent.

Exclusion Criteria:

* for PD patients: (1) presence of other neurological disorders, (2) any cardiovascular and respiratory system restrictions and/or motor deficits that could limit performance in high-speed pedaling on a cycle ergometer or in the conventional physical therapy and (3) practicing any regular intensive physical activity except for physical therapy for PD
* for healthy controls: presence of neurological disorders
* for all tested subjects, an additional exclusion criterion for the PET and fMRI experiments will be a claustrophobia.