2 December 2011
Stevens-Lapsley
J, Kluger BM, Schenkman M
Background: People with Parkinson disease (PD) typically have complaints of weakness. The mechanisms underlying this deficit have not
been well established, although many factors may contribute.
Objective:
This investigation aimed to characterize quadriceps muscle weakness and
activation failure in people with PD and explore
whether these deficits were related to disease
severity. The authors further sought to examine quadriceps muscle
fatigability.
Methods: This was a cross-sectional
comparison of 17 people with mild-severe PD and 17 healthy adults
matched by age, sex, and body
mass index (BMI). The Unified Parkinson’s Disease
Rating Scale motor score (UPDRS motor) ranged from 9.5 to 61.0.
Participants
were divided into those with low-PD motor signs
(UPDRS motor < 31.7) and high-PD motor signs (UPDRS motor ≥ 31.7).
Measures
of quadriceps performance included isometric
torque, central activation using doublet interpolation, and an
isokinetic fatigue
test.
Results: Participants with high-PD
motor signs had significantly more quadriceps weakness and central
activation deficits than those
with low-PD motor signs or healthy controls.
Strength and activation deficits correlated strongly with UPDRS motor
score.
Quadriceps muscle fatigue was present in healthy
controls and in those with low-PD motor signs but not in those with
high-PD
motor signs.
Conclusions: These findings
provide additional evidence for lower-extremity strength loss with PD;
central activation deficits may account
for some of the strength deficits, especially with
increased PD motor signs. Also, muscle fatigue did not occur in
individuals
with a greater degree of PD motor signs, most
likely because of insufficient central activation to allow for muscle
overload
to induce metabolic fatigue.
