Determinants of Physical Frailty in Parkinson's Disease: A Multi-Factorial Analysis

Motor imagery ability will be assessed using the Vividness of Movement Imagery Questionnaire-2 (VMIQ-2), a validated self-report instrument with established Turkish validity and reliability. The questionnaire consists of 12 items assessing the vividness of imagined movements across three domains: external visual imagery, internal visual imagery, and kinesthetic imagery. Each item is rated on a 5-point Likert scale (1-5), and separate scores are calculated for each subscale as well as a total score. Total scores range from 17 to 68, with higher scores indicating lower vividness of motor imagery ability. Assessments will be administered jointly by the responsible physician and a physiotherapist.

Interoceptive body awareness will be assessed using the Multidimensional Assessment of Interoceptive Awareness-2 (MAIA-2), a validated self-report instrument with established Turkish validity and reliability. The Turkish version consists of 34 items across seven subscales: Noticing, Not-Distracting, Attention Regulation, Emotional Awareness, Self-Regulation, Body Listening, and Trusting. Each item is rated on a 6-point Likert scale ranging from 0 (never) to 5 (always). Subscale scores are calculated separately, with higher scores indicating greater interoceptive body awareness in the respective domain.

Physical frailty will be assessed using the Fried Frailty Phenotype (FFP), a validated measure based on five criteria: unintentional weight loss, exhaustion, low physical activity, weak handgrip strength, and slow walking speed. Participants will be classified as robust (0 criteria), prefrail (1-2 criteria), or frail (≥3 criteria). Each criterion will be scored as present or absent, and a total score ranging from 0 to 5 will be calculated. In addition to the original criteria, population-specific cut-off values for handgrip strength (≤13.6 kg for women and ≤27.7 kg for men) will be applied. Higher scores indicate greater frailty.

Kinesiophobia (fear of movement) will be assessed using the Tampa Scale for Kinesiophobia (TSK), a validated 17-item self-report questionnaire evaluating fear of movement and re-injury. Each item is rated on a 4-point Likert scale (1 = strongly disagree to 4 = strongly agree). The total score ranges from 17 to 68, with higher scores indicating greater fear of movement. The Turkish version of the scale has demonstrated validity and reliability in clinical populations.

Physical activity level will be assessed using the Physical Activity Scale for the Elderly (PASE), a validated self-report questionnaire designed to evaluate physical activity in older adults. The scale consists of 12 items covering leisure time activities, household activities, and work-related physical activities performed over the previous 7 days. The total PASE score is calculated by multiplying activity frequency and duration by empirically derived item weights and summing across all activities. Scores range from 0 to over 400, with higher scores indicating higher levels of physical activity.

Symptom severity will be assessed using the Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS), a validated instrument evaluating motor and non-motor aspects of Parkinson's disease. The scale consists of four parts covering non-motor experiences of daily living, motor experiences of daily living, motor examination, and motor complications. Each item is rated from 0 (normal) to 4 (severe), and total and subscale scores are calculated. Higher scores indicate greater disease severity.