Muscle shape changes in Parkinson's disease impair function during rapid contractions

Area of Science:

• Neurology
• Biomechanics
• Kinesiology

Background:

• Parkinson's disease (PD) is a neurodegenerative disorder causing muscle weakness and reduced torque.
• PD patients exhibit slower rates of torque development (RTD) during explosive contractions.
• Understanding peripheral factors contributing to rapid force generation deficits in PD is crucial.

Purpose of the Study:

• To investigate how peripheral, structural, and mechanical factors in knee extensor muscles contribute to impaired rapid torque development in Parkinson's disease patients.
• To compare dynamic muscle shape changes, muscle-tendon unit (MTU) stiffness, and EMG activity between PD patients and healthy controls.

Main Methods:

• Participants performed maximal voluntary explosive knee extensor contractions.
• Measured dynamic muscle shape (thickness, pennation angle, belly gearing), MTU stiffness, and vastus lateralis (VL) EMG.
• Assessed both affected (PDA) and less affected (PDNA) limbs in PD patients.

Main Results:

• Controls generated higher peak torque and faster RTD than PD patients (PDA and PDNA).
• EMG differed between PDA and controls, suggesting neural effects on the affected side.
• MTU stiffness and muscle shape changes differed between controls and PD patients (both sides), indicating similar peripheral impairment.

Conclusions:

• Higher MTU stiffness in PD patients likely reduces muscle shape adaptability.
• This impaired muscle shape change negatively impacts the rate of torque development.
• Peripheral factors, specifically MTU stiffness, play a significant role in the motor deficits observed in Parkinson's disease.