Voluntary activation of the knee extensors in chronic poststroke subjects.
OBJECTIVE
To assess the extent to which knee extensor muscle weakness in subjects with chronic mild to moderate poststroke hemiparesis is caused by a decreased voluntary activation.


METHODS
Forty community dwelling and ambulant men and women (mean age, 59.8 +/- 5.5 yrs) with residual hemiparesis (19.2 +/- 8.5 mos poststroke) were tested. Torque measurements were performed on a computerized dynamometer and the superimposed electrical stimulation technique was used to assess voluntary activation of the knee extensors in both the paretic and the nonparetic lower limbs.


RESULTS
The mean voluntary activation ratio of the knee extensors in the nonparetic and paretic leg was 0.97 +/- 0.04 and 0.86 +/- 0.13, respectively. Subjects who had a greater relative weakness, implying a more pronounced poststroke impairment, also had lower voluntary activation ratios. The mean percentage difference in total torque between the nonparetic and the paretic knee extensors after the electrical stimulation was 36.4% +/- 17.0%.


CONCLUSIONS
Paretic knee extensor muscle weakness in chronic poststroke subjects is only partially explained by a reduced voluntary activation ability, indicating that other neuromuscular structural or functional factors contribute to poststroke hemiparetic muscle weakness.
Miller
Michael
M
Division of Physical Therapy, Lund University, Lund, Sweden.
Flansbjer
Ulla-Britt
UB
Lexell
Jan
J
D002908:Chronic Disease; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D006984:Hypertrophy / Q000503:physiopathology; D007717:Knee / Q000294:innervation / Q000503:physiopathology*; D007719:Knee Joint / Q000294:innervation / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength; D053581:Muscle Strength Dynamometer; D018482:Muscle, Skeletal / Q000503:physiopathology*; D010291:Paresis / Q000503:physiopathology* / Q000534:rehabilitation; D020521:Stroke / Q000503:physiopathology*; D000071939:Stroke Rehabilitation; D013997:Time Factors