Table 1 Inclusion and exclusion criteria

▪ Diagnosis of idiopathic, typical PD according to the United Kingdom Brain Bank Criteria [20]

▪ Modified Hoehn & Yahr stages 1–3 (mild to moderate disease severity) [21]

▪ Live in the community

▪ Able to walk 10 continuous minutes without help from another person

▪ Stable on all PD medications for at least two weeks prior to study entry

▪ Moderately or significantly disturbing freezing episodes during daily walking (score of ≥ 2 on item 7 of the New Freezing of Gait Questionnaire (nFOGq)) [22]

▪ Significant cognitive impairment (i.e., Mini-Mental State Examination (MMSE) score of < 24) [23]

▪ Unstable medical or concomitant illnesses or psychiatric conditions, which in the opinion of the investigators would preclude successful participation

▪ Cardiac problems that interfere with ability to safely exercise (i.e., uncontrolled congestive heart failure, complex cardiac arrhythmias, chest pain or pressure, resting tachycardia (> 120 beats/min), uncontrolled BP (resting systolic BP > 180 mmHg or diastolic BP > 100 mmHg))

▪ Orthopedic problems in the lower extremities or spine that may limit walking distance (i.e., severe arthritis, spinal stenosis or pain)

▪ Engaged in a walking program for greater than 90 min per week for the past month

▪ Engaged in an exercise regime of moderate intensity for greater than 90 min per week for the past month