The purpose of this thesis was to determine whether practice-induced adjustments and
retention of a goal directed isometric motor accuracy task were similar between ipsilateral upper
and lower limb and whether there is an ipsilateral transfer between upper and lower limbs. In
addition, this thesis project aimed to determine whether motor output variability and the activity
of the involved agonist and antagonist muscles could predict any of the above stated changes.
Sixteen young adults (8 men, 8 women; 22.1 or - 2.1 years) performed 80 trials of goal directed
isometric contractions that involved accurately matching a target force of 25% MVC in 200 ms,
either with the upper limb or the lower limb followed by the other limb. After an interval of 48
hours, 10 trials similar to the practice trials were performed to examine retention. Feedback of
performance was provided in the form of a force-time trajectory along with numerical error
values for force and time on each trial. End-point error was quantified as the absolute deviation
from the targeted force and time. Motor output variability was quantified as the SD of force, SD
of time to peak force and SD of force trajectory.
The practice-induced adjustments for force and time endpoint accuracy were similar for the
two limbs, however, two days later, retention of the force accuracy was better with the upper
limb compared with the lower limb. Practice-induced reduction and practice-to-retention increase in force and time endpoint error were predicted by respective changes in peak force and
time to peak force trial-to-trial variability for both limbs. In addition, the changes in accuracy
were predicted by the changes in the activity of the involved agonist and antagonist muscles.
Nonetheless, the changes in muscle activity differed between the two limbs. The adjustments in
muscle activity were also different during the practice session despite the fact that the rate of
improvement was similar for the two limbs. Finally, there was an asymmetric transfer of force
accuracy from the lower limb to the ipsilateral upper limb, which was associated with the
changes in motor output variability. The upper limb, which is inherently less variable as
compared to the lower limb, may have retained the task better due to the formation of a stronger
muscle synergy (or stronger internal model) to perform the contractions with accuracy. The
lower limb, on the other hand may have formed a weaker internal model due to the greater
interference from amplified signal-dependent noise (motor output variability) or an alternative
motor plan, which may have been concerned primarily with the minimization of motor output
variability instead of formation of a muscle synergy to perform the contractions accurately.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-05-303 |
| Date | 2009 May 1900 |
| Creators | Kaur, Navneet |
| Contributors | Christou, Evangelos |
| Source Sets | Texas A and M University |
| Language | English |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | application/pdf |
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