Experiment Protocol:
MECHANICAL CONTRIBUTION OF THE TIBIALIS
ANTERIOR STRETCH REFLEX
Purpose
The mechanical contribution to joint stiffness of the stretch
reflex has been previously studied in the gastrocnemius-soleus muscle. In
contrast, the antagonist muscle, tibialis anterior, has not been characterized.
The objective of this experiment is to explore the mechanical significance
of the tibialis anterior stretch reflex.
Description
- Custom Ankle Boot. A
custom-fit fibreglass boot is used to securely attach the subject's foot
to the actuator in the experimental apparatus. Orthopedic casting tape is
molded to the subject’s left foot and ankle. Following a setting period,
a cast cutter is used for removal. This preparation will be no longer than
90 minutes on a day prior to experimentation.
- Range of Motion. The
ankle is rotated passively from a neutral position towards maximum dorsiflexion
and then towards maximum plantarflexion.
- Maximum Voluntary Contraction
(MVC). Subjects are required to generate both dorsiflexing and plantarflexing
maximum voluntary contractions in response to changes in a tracking stimulus
displayed on an oscilloscope.
- Level of Contraction. Subjects
are asked to generate and apply ankle torques of 5-30% of the tibialis anterior
MVC while the position perturbations are applied.
- Position Stimuli. Four
types of position input will be used to stimulate the ankle.
- Pulse trials: At each pulse onset, the subject's foot will
be subjected to a 40 ms pulse with amplitudes of 0.03-0.1 radians.
- Step trials: A step input will subject the foot to a sudden
stretch of 0.03-0.1 radians and maintain that position for 1 s before
returning to the starting position
-
Random perturbations with superimposed pulses
trials: Random perturbations, with maximum amplitude of 0.005-0.05
radians and a bandwidth of 10-65 Hz will be applied in combination
with the pulse trials.
-
Random perturbations with superimposed step trials:
Same as iii., but in combination with step trials instead of pulse
trials.
- Usually, the experiment will last for less than 120 minutes including
a 30 - 40 min preparation period.
- Subject may ask for a rest or withdraw from the experiment at any time.