Carvell, PhD, PTUniversity
Motor Control Strategies and Task Demands III
See Brooks Fig.
1.3, p 10
Slow movements tend to be
feedback-assisted or feedback-guided. Motion paths are 'discontinuous'. Velocities tend
to be multi-peaked. EMG is often characterized by repeated Agonist 'steps' with little
contribution by the antagonist, although the pattern differs according to the stiffness
required and/or the action sequence required (cyclic vs. non-cyclic). Slow
'discontinuous' movements may be used: 1. when one is a novice, 2. when one is uncertain how
to proceed, 3. when errors creep into previously 'automatic' skilled actions, or 4.
when absolute accuracy is a must. Moderate to fast movements are
thought to be programmed with the potential for but not a requirement of, feedback
adjustments. Feedback may be used as 'knowledge of results' on the next trial.
Motion paths are 'continuous' smooth transitions from beginning to end. EMG is triphasic:
1st Agonist burst followed by an Antagonist burst followed by a 2nd Agonist burst.
This triphasic pattern results in a single velocity peak. The antagonist EMG activity
and movement velocity peak simultaneously. These 'continuous' movements are used when
skill has been obtained, when one is confident in how to proceed, and environmental
factors or task demands have not changed. If speed and accuracy are essential a
slightly reduced speed and use of feedback for minor adjustments may be required as
the movement proceeds.
Brooks Fig 1.5 p
1.5 shows the progression
strategies used by
a monkey while learning
a simple move and hold
task. Note the transition
from slow discontinuous
to fast continuous
movements as the
monkey gains ‘insight’
into the requirements
for the task and the
motor program is