**Effect of Trunk Flexion on Airway Defense in Parkinson's Disease** People with Parkinson's Disease (PD) often have trouble with swallowing (called *dysphagia*) and coughing (*dystussia*). These issues can lead to serious lung problems like aspiration pneumonia, which is a major cause of death in PD patients. This study looks at how a posture issue called forward trunk flexion (FTF) affects breathing and coughing in people with PD. FTF is when the body leans forward more than 30 degrees. It can make it hard for PD patients to swallow and cough properly. This study will check if FTF weakens the muscles used for breathing and coughing. **Key Points:** - Study will last up to three years with regular check-ups. - Participants must be at least 18 years old with a diagnosis of PD. - Some tests will check muscle strength and breathing. If you have Parkinson's and a forward-leaning posture, this study might help understand how it affects your breathing and coughing. However, if you have other serious health issues, you might not be able to join.