Central factors explain muscle weakness in young fallers with Parkinson's disease.

Background: Muscle weakness in old Parkinson's disease (PD) patients has been shown to impair their mobility, although the specific origin of this weakness and its relation to falls has not been well examined in young patients.

Objective: This study aimed to analyze the possible contribution of central factors to muscle weakness of the triceps surae and quadriceps femoris muscles in young faller and nonfaller PD patients.

Methods: Twenty-six young PD patients (fallers, n = 13 and nonfallers, n = 13) and 15 matched healthy controls performed several isometric maximal voluntary knee extension and plantar flexion contractions (MVC) of the most affected leg on a dynamometer. We estimated the maximal resultant agonist moments, the antagonistic moment of hamstrings and tibialis anterior during MVCs and the activation deficit of the quadriceps femoris and triceps surae muscles.

Results: Only the Parkinson fallers showed significantly lower muscle strength, higher antagonistic moments and higher activation deficit compared with controls. Multiple regression analysis showed that the antagonistic moments and the activation deficit explained about 39% and 27%, of the variance in the maximal resultant moments of the knee extensors and the plantar flexors, respectively.

Conclusions: Our findings suggest that Parkinson fallers are affected by strength impairments arising from the central nervous system and not from the peripheral muscle contractile capacity, even at early stages of the disease and young age. High-intensity resistance training may help enhance neural drive and decrease unwanted antagonistic moments and reduce the risk of falls.