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

Skinner, Jared W., PhD; Christou, Evangelos A., PhD; Hass, Chris J., PhD

Journal of Neurologic Physical Therapy: January 2019 - Volume 43 - Issue 1 - p 56–62
doi: 10.1097/NPT.0000000000000244
Research Articles

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:

Geriatric Research Education and Clinical Centers, Malcom Randall VA Medical Center, Gainesville, Florida (J.W.S.); and Department of Applied Physiology and Kinesiology, University of Florida, Gainesville (E.A.C., C.J.H.).

Correspondence: Jared W. Skinner, PhD, North Florida/South Georgia Veterans Health System, Geriatric Research, Education, and Clinical Centers (GRECC) (182), 1601 SW Archer Rd, Gainesville, FL (

The authors declare no conflict of interest.

Supplemental digital content is available for this article. Direct URL citation appears in the printed text and is provided in the HTML and PDF versions of this article on the journal's Web site (

© 2019 Academy of Neurologic Physical Therapy, APTA