Influence of Contraction Type, Speed, and Joint Angle on Ankle Muscle Weakness in Parkinson's Disease: Implications for Rehabilitation

Pang MY, Mak MK. Influence of contraction type, speed, and joint angle on ankle muscle weakness in Parkinson's disease: implications for rehabilitation. Arch Phys Med Rehabil 2012;93:2352-9. Objective: To compare the ankle muscle strength and torque-angle relationship between individuals with Parkinson's disease (PD) and participants without impairments. Design: Cross-sectional, exploratory study. Setting: Motor control laboratory in a university. Participants: Convenience sample of community-dwelling individuals with PD (n=59) recruited from a PD self-help group and age-matched participants without impairments (n=37) recruited from community older adult centers. Interventions: Not applicable. Main Outcome Measure: Peak torque and angle-torque profile during concentric and eccentric contraction of ankle dorsiflexors and plantarflexors at 2 different angular speeds (45 and 90 degrees/s). Results: The PD group displayed lower muscle peak torque values than participants without impairments in all test conditions. Generally, concentric strength was more compromised, with a greater between-group difference (Cohen d=1.29-1.60) than eccentric strength (Cohen d=.81-1.37). Significant group by angular speed interaction was observed in ankle plantarflexion concentric peak torque (P<.001), indicating that muscle weakness was more pronounced when the angular speed was increased. The group by joint angle interaction in concentric contraction of ankle plantarflexors at 90 degrees/s was also significant (P<.001), revealing that the between-group difference in torque values became increasingly more pronounced when the joint was moving toward the end range of the ankle plantarflexion. This exaggerated ankle plantarflexor muscle weakness at the end range was significantly correlated with clinical balance measures (P<.05). Conclusions: Muscle weakness in PD is influenced by contraction type, angular speed, and joint range. Exaggerated weakness is found in concentric contraction of ankle plantarflexors, particularly when the angular speed is high and the muscle is in shortened lengths.