Changes in distal muscle timing may contribute to slowness during sit to stand in Parkinsons disease

Objective. To compare patterns of muscle activation in the lower extremity and subsequent forces during sit to stand in persons with Parkinsonism. Background. There is an interruption of the tibialis anterior/soleus interaction during forward oriented movements in some subjects with Parkinsonism, including sit to stand. This task is a major determinant of independence and 44% of those with Parkinsonism report difficulty. Methods. 41 subjects with Parkinsonism were asked to stand up from a bench. Peak acceleration and vertical ground reaction forces, the slopes to these peaks, and the timing of events were measured. Surface electrodes were placed on tibialis anterior and soleus. Results. The slower group produced force at slower rate than the fast group. The slower group spent 64% of the time taken to stand to complete the flexion-momentum phase, and the fast group spent 56%. The slower group had a larger proportion of co-contraction trials than the other groups. Conclusions. Slower subjects took longer to perform the task due to a longer time for seat off. Deficits recruiting tibialis anterior may contribute to the decreased rate of production of the acceleration forces and the longer time required for seat off.