Motor cortical control of antagonist muscle function in aging

There is overwhelming evidence that for some reason increasing age affects a
key aspect of how humans produce voluntary force. During finger, wrist, elbow,
knee, and ankle joint movements old compared with young adults execute weak and
strong contractions so that the muscle that is antagonist (opposing) to the
muscle that produces the movement (the agonist), becomes more strongly
activated. The neural mechanism of this age-related increase in coactivation is
unknown. One example for the functional significance of this age-driven altered
movement strategy is the strong association between the 20% greater metabolic
cost of transport and heightened antagonist leg muscle activation during gait
in old compared with young adults. The hypothesis is that motor cortical
control of antagonist muscle function alters with age.

To examine the motor cortical control of antagonist muscle function in younger
and older adults

In this study, a rapid flexion of the wrist will be used as a voluntary
movement to examine the amount of coactivation in the lower arm muscles. The
cortical excitability before and during the movement will be measured with
transcranial magnetic stimulation (TMS).

Participants respond to a tone by rapidly flexing their right-dominant wrist. A
single TMS is given with 20 ms increments between 80 to 380 ms after the tone.
Pilot experiments showed that old individuals were able to reliably execute the
reaction time task if administered in 3 blocks of 68 trials, a total of 204
trials with 3-5 minutes of rest between the blocks. In 1 of the 17 conditions,
only the tone is presented and in the 16 other time-interval conditions a
single TMS pulse is delivered, targeting the right wrist muscles. There are 12
trials in each of the 17 conditions, with the condition administered in a
random order. The data are then sorted in to 10 ms bins. The participants will
visit the Center for human movement sciences once during an approximately 2
hour lasting session.

Non-invasive flexion of the right hand after hearing an auditory tone.
Measuring the cortical excitability indexed by the size of the motor evoked
potentials (MEPs) produced by transcranial magnetic stimulation (TMS).

Participants will visit the Center for Human Movements Sciences once. The
duration of the session is approximately 2 hours. TMS may cause slight
discomfort lasting less than a second on the scalp near the coil. It may also
cause twitching of the muscles, the face and jaw, which may be unpleasant and
surprising but not painful. There are no known long-term risks of magnetic
brain stimulation. For participating in the study, participants receive 10
euros in form of VVV gift cards.