Parkinson's disease (PD) is the second most common neurodegenerative disease, characterized clinically by motor and non-motor symptoms, including bradykinesia, resting tremor, and/or rigidity. Among the motor deficits observed in PD, decreased postural control often results in decreased balance. Furthermore, losses in many upper extremity and manual skills are also observed in PD. Loss of postural control is one of the key motor symptoms observed in the advanced stages of PD, increasing the risk of falls. Analysis of postural control deficits is critical for assessing disease progression and treatment planning in PD. In this context, gyroscope-based motion analysis systems are used as a reliable method for assessing trunk sway.Sensory deficits, such as decreased spatial and temporal tactile discrimination thresholds in the fingertips, are also observed in PD. Reaching and grasping deficits are more common when patients have significant difficulty initiating movements toward a target. These patients exhibit deficits in manipulating the hand relative to object geometry. A loss of coordination between reach and grasp timing is observed. These patients generally rely on visual cues to control movement. They experience difficulties in optimal object manipulation due to difficulties planning finger placement.Studies have shown a strong relationship between postural control and fine motor functions. For high-quality distal movement, better proximal stabilization is necessary. During upper extremity functions, the body's center of gravity must shift with arm movements, allowing adaptation to changing gravity. Good trunk control is essential for this dynamic process of maintaining balance. Studies examining this link between trunk control, balance, and hand functions are available in the literature. Among these studies conducted in diverse populations, studies involving PD are very few. In light of this information, our study was designed to investigate the relationship between postural trunk sway and hand dexterity in PD. Therefore, the aim of this study was to determine the relationship between postural sway and upper extremity functional abilities in PD.

Inclusion Criteria:

• Healthy individuals aged 40-75 years, diagnosed with idiopathic PD according to the UK Parkinson's Disease Association Brain Bank criteria by a specialist neurologist, with a Modified Hoehn & Yahr (m-HY) scale stage ≤4, and with a Mini Mental State Examination score of ≥22 for those with training and ≥18 for those without training, and with no known disease, volunteered to participate in the study.
• Individuals with no other known neurological and/or systemic disease
• Individuals without any upper extremity contractures

Exclusion Criteria:

• Individuals with severe balance and walking difficulties
• Individuals with diagnosed and/or treated psychiatric illnesses who are considered unable to complete the required tests
• Those taking neuroleptic medications or antidepressants
• Individuals with orthopedic conditions that interfere with manual dexterity tests, such as severe dyskinesia, carpal tunnel syndrome, tendon injuries, or finger amputations; rheumatological diseases such as rheumatoid arthritis and osteoarthritis; and individuals with any neurological disease other than PD

Individuals aged between 40 and 75 years (n=40±5) who applied to the Neurology Clinic of the Faculty of Medicine of KSÜ Training and Research Hospital, diagnosed with Idiopathic Parkinson's disease (PD) by a neurologist, having stage ≤4 on the Modified Hoehn&Yahr (m-HY) scale, and having scores of ≥22 in the educated and ≥18 in the uneducated according to the Mini Mental State Examination, and healthy individuals of a similar age group (n=40±5)