The influence of instructions and expectations on a maximal fatiguing task

In many studies, participants are asked to produce maximal force. This test can
give information on for example muscular strength and endurance. In the past,
several variables have been studied that can influence the outcome of a
fatiguing task. It is shown that encouragement during the task leads to
improved performance (Andreacci et al 2002). Also the instructor can influence
the performance on a fatiguing task (Jung et al 2009) or the feedback about the
duration of exercise (Morton 2009). In a study of Sahaly and colleagues (2001),
subjects received two different instructions regarding force production; either
as hard and fast as possible, or as fast as possible (after which the subjects
were stimulated to reach the maximum). This study found a clear difference in
performance between both instructions.
More evidence arises to support the notion that maximal performance is not only
depending on muscular strength, but is also influence by non-physiological
parameters.
However, it is still unclear whether the instruction to produce maximal force
influences the performance. Such an instruction often leads to subjects
preparing for the production of a large amount of force. Whether this component
influences the maximal force or the activation of the muscle, will be examined
in this study. We expect that the instruction to produce maximal force will
lead to a different activation pattern of the muscles and a difference in
performance compared to an instruction to produce force according to a given
pattern.

What is the influence of instructions and expectations on produced force and
muscle activation during a fatiguing task?

During both sessions, the strength (using a force recorder) and muscle activity
(using EMG-electrodes) of the abductor of the right index finger (FDI) are
measured . Simultaneously, the nerve innervating the muscle will be
electrically stimulated. The subjects will come for two sessions. During the
first session, they will be instructed to produce maximal force for two
minutes. The second session they will be instructed to keep the force similar
to a presented force level, that (without the subjects being aware of this)
corresponds to the maximal force of the first session.

Fatigue task

No risk, time investment for the subject is 2*0.5 hours is 1 hour.