Lower Extremity Muscle Strength and Force Variability in Persons With Parkinson Disease

Background and purpose Adequate lower limb strength and motor control are essential for mobility and quality of life. People with Parkinson disease (PD) experience a significant and progressive decline in motor capabilities as part of this neurodegenerative disease. The primary objective of this study was to examine the effect of PD on (1) muscular strength and (2) force steadiness in muscles that are primarily responsible for locomotion and stability. Methods Thirteen persons with PD and 13 healthy age-matched controls participated. Participants performed maximal and submaximal (5%, 10%, and 20% maximum voluntary contractions) isometric force tasks with the limb stabilized in a customized device. Strength of the hip extensors and flexors, hip abductors and adductors, and ankle plantar flexors and dorsiflexors was quantified based on data obtained from force transducers, with the relevant joint stabilized in standardized positions. Results Individuals with PD were weaker and exhibited higher amounts of force variability than controls across the lower extremity. Reduced strength was greatest in the hip flexors (2.0 N/kg vs 2.6 N/kg) and ankle plantar flexors (1.74 N/kg vs 2.64 N/kg) and dorsiflexors (1.9 N/kg vs 2.3 N/kg). Force steadiness was impaired in the hip flexors, ankle plantar flexors, and dorsiflexors. Discussion and conclusions Reduced maximal force production was concomitant with impaired force control within the muscles that are critical for effective ambulation (hip flexion, ankle dorsiflexion, and ankle plantar flexion). These features should be evaluated when considering contributors to reduced mobility and quality of life.Video Abstract available for more insights from the authors (see Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A241).