<p>Stability is the ability of a system
to reject noise and maintain or return to the desired movement pattern and is
an important feature of a motor system. In contrast, maneuverability is the
ability of a system to transition between different motor states. A system that
prioritizes stability inhibits its ability to transition between different
motor states in a dexterous fashion. Since stability and maneuverability are opposing
characteristics of a system, stability could be traded off to increase
maneuverability. This
study focuses on isometric finger force production, and its goals were to
identify whether (1) the amount of information available about an upcoming
motor transition influences the reduction in stability of total isometric force
produced by the fingers, (2) stability reduction was correlated with greater
maneuverability, i.e., less time for initiating a change in the total force,
(3) the amount of stability reduction is correlated across tasks with different
amount of information regarding the upcoming force changes, and (4) the times
required to change force correlated across tasks with different informational
content. </p>
<p>Twenty-nine young
adults (17 women; age, 23.3 ± 4.3 years) participated in this study and
completed three different finger force tasks. For each task, the participants
modulated the total pressing force produced by the four fingers of their right
hand to track a target presented on a computer screen. In each task,
participants began by producing a consistent (10% of their maximum voluntary
contraction, MVC) background force with their fingers. In the Steady task, the
target remained stationary and participants knew the target would not move. In
the Reaction Time (RT) task, the target moved randomly in the vertical
direction and participants knew that this could happen at any point in time. In
the Self-paced task, participants started producing a background force and then
produced a quick increase in total force using a predefined target that was
displayed at the beginning of the trial, and visible throughout the trial. </p>
<p>The uncontrolled
manifold analysis was used to assess the stability of the total force during
each task. This assessment was performed when the participants produced the same
force (10% MVC), but expected different upcoming force changes, and had
different amount of information about these upcoming force changes. This
analysis yielded a stability index, and measures of the variance structure in
the finger forces, computed across multiple repetitions. The reaction time and
the movement time in the RT and the Self-paced tasks, respectively, was
computed to quantify maneuverability. </p>
<p>In contrast to
previous findings and our expectations, the stability index was not statistically
different for the Steady, RT, and Self-paced tasks, meaning that stability of
the total force was not reduced in response to the mere expectation of an
upcoming change in total force. However, the stability index reduced immediately
before individuals changed their total force in the Self-paced tasks, which supports
findings from previous studies. The stability modulation between the Steady and
RT tasks did not correlate with the RT, and the stability modulation between
the Steady and Self-paced tasks did not correlate with the movement time. Therefore,
this study did not reveal a stability-maneuverability trade-off in isometric
finger force production tasks. The movement time for the RT and Self-paced
tasks were also not correlated. However, the novel finding of this study was
that participants changed stability similarly for the RT and Self-paced tasks.</p>
<p>Finally, the
variance components obtained from the uncontrolled manifold analysis were
higher in the RT task compared to the Steady task, consistent with previous
reports. In fact, the increase in the performance error (greater variability in
total force) while expecting to change total force in uncertain conditions (RT
tasks) is the most striking and consistent result across multiple similar studies.
This result indicates that despite the inconsistent results regarding the stability
index, the performance of the current task (producing a constant total force)
is hampered by the uncertainty and the expectation of upcoming changes in total
force.</p>
<p>It is likely that the
stability-maneuverability trade-off is not essential for young, healthy adults
in manual force production tasks. Investigations that include participants
across the lifespan will shed light on this relation and help identify whether
it plays a salient role in understanding loss of manual dexterity with healthy
aging. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/14502228 |
| Date | 06 May 2021 |
| Creators | Paige A Thompson (10716468) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/STABILITY_MODULATION_IN_FINGER-FORCE_PRODUCTION_TASKS/14502228 |
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