Carvell, PhD, PTUniversity
Motor Control Strategies and Task Demands II
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).
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.
movements, by definition, are
brief and very fast (movement time <200 msec). Skilled self-terminated ballistic movements are thought to
with no feedback assistance
once they are launched. Motion
paths are smooth, rapid transitions
from start to finish. EMG is biphasic
with an Agonist burst followed by
an Antagonist burst that corresponds temporally to the velocity peak. Ballistic movements are not the usual choice
for most things you
do. However, when speed is
essential you need to go ballistic.
If these movements are not practiced
they will be relatively and absolutelyinaccurate. With practice skilled ballistic movements become relatively more accurate. With
talent and practice,
ballistic motions become relatively
& absolutely more error-free.