Influence of task manipulation on muscle activity

When producing large amounts of force or during a sustained submaximal
contraction except from contractions in the target-muscle also non-target
muscles are activated. There are even muscles activated who are contralateral
to the 'target' muscle (CAC, contralateraal associated contraction) (Gellhorn
1947; Dimitrijevic et al. 1992; Gandevia et al. 1993; Mayston et al. 1999;
Zijdewind and Kernell, 2001). A recent study proved the contralateral motor
cortex activated both the associated contractions and the voluntary
contractions (Zijdewind, 2006).
Associated contractions are often researched with tasks which are known to
influence the amount of CAC, like making contractions at different force levels
or fatiguing the target muscle. However, during these kind of tasks all other
kinds of processes can influence the outcome of the CAC research. For this, it
would be very good to have a task were at a similar force level or fatigue
level there is yet more CAC.

In this pilot experiment we want to see in which way we have to manipulate a
task it that way that we have more CAC although the amount of force or fatigue
in the target muscle is the same.

In this research we want to try different research protocols in order to see
which task is the best to influence the amount of CAC. The tasks shall be
executed in the same but sometimes in different sessions. Because of the
fatigue which arises in three of the tasks, it is not possible to execute all
tasks in one measure session. Because of this a part of the tasks will be
executed in another measure session on another day. During all tasks force and
EMG measurements of the FDI muscle will be executed. As well shall all subjects
before all tasks be asked to make a maximal contraction with the left an right
index finger.
For task 6 we will also measure the force of one of the feet and the EMG of
accompanying tibialis anterior and gastrocnemicus muscle. Furthermore, the
maximal contraction of the foot will be determined.
Task 1: Subjects will be asked to follow as good as possible a pyramid shaped
line with the force of one index finger.
Task 2: Subjects will be asked to make a small contraction with the non-target
FDI muscle while the target muscle makes contractions at different force levels.
Task 3: Subjectes will be asked to make 10 contractions of 15 seconds at 30% of
their maximal contraction. The Gain of the screen at which the subjects recieve
visual feedback will be changed, in order to make the task more difficult.
Task 4: In two sessions, subjects are asked to make a fatiguing contractions
during which the target hand will be in same position, but the non-target hand
will be change position between sessions. Similar hand positions would
presumably result in more CAC.
Task 5: Subjects are asked to make a sustained contrantraction at 50% of their
maximum force. They receive visual feedback of their force, however, they don't
see the force of the target hand but the force of both hands add up together.
With this protocol we can possibly influence the amount of CAC.
Task 6: Not the hand, but the foot will be fatigued, to see what the influence
is on the amount of CAC in the hands.

There are no risks