Interaction between motor and cognitive performance during motor fatigue in MS en MG patients.

Motor fatigue is an important symptom in neuromuscular diseases and movement
disorders. Despite its impact, still little is known about motor fatigue in
neurological disorders. Furthermore, even less is known about the secondary
effects of motor fatigue on e.g. cognitive performance. In this proposal, we
intend to investigate motor fatigue in Myasthenia Gravis (MG) and Multiple
Sclerosis (MS) because these two disorders are at either end of the continuum
from fatigue caused by peripheral (MG) to central (MS) factors.

In both MG and MS patients groups we expect to find signs of central fatigue.
The contribution of central fatigue to the general feeling of fatigue is
expected to be more pronounced in MS-patients than in MG-patients. The
secondary effects of motor fatigue on cognitive performance may be increased in
both MG and MS-patients compared to control subjects. Knowledge about these
aspects of fatigue is extremely important from a fundamental and clinical point
of view. Furthermore, improved knowledge about motor fatigue is important for
the well-being of the patients and their caregivers. In this study, we plan to
investigate effects of motor fatigue on central activation patterns and
related, secondary effects of motor fatigue on cognitive performance. In our
opinion, cognitive performance could be seriously affected by increased demands
on central processing resources due to motor fatigue.

Central and peripheral effects of motor fatigue are investigated by a
dual-task paradigm. Subjects are asked to produce various force levels with
their right index finger while they perform a choice reation time task with
their left hand. Possible interactions between the performance of the two taks
are studied in 3 sessions. Session I is used to familiarize the subject with
the experimental setup. Subjects have to produce a maximal contraction with
their right index finger an perform a non-fatiguing contraction for 15 s
combined with ah choice reaction time task. Session II is a repetition of
session I. In the third session the choice reaction time task is combined with
a fatiguing motor task. Subjects have to maintain a 30% of maximal force for 1
minute in combination with the choice reaction time task. Afterward they have 4
s rest and then they have to perform the same task again. This is repeated
until the subject can*t maintain the 30% force any longer. At the end of the
fatiguing contraction subjects have to perform 1 maximal contraction.

Subjects perform a fatiguing motor task in combination with a choice reaction
time task.

No risks are involved in this experiments; the experiments take time from the
subjects. Subjects have to come to the lab 3 times and each visit takes about
1.5 hours.