[Abstract Title]. - Society for Neuroscience

determine the maximum load they could lift. Next, subjects were asked to hold their hand in a
horizontal position (forearm supported and secured) while supporting one of four test loads (0%,
5%, 15% and 25% 1-RM; order of presentation randomized). For each load, two 16 s trials were
collected with a 2-min break between each trial. Postural tremor was measured with a LASER
displacement sensor and wrist extensor activity was recording using electromyography (EMG).
Repeated-measures ANOVA was used to determine group and load effects on dependent
measures (postural tremor amplitude and time-dependent structure; postural tremor and EMG
spectral measures). Results: There was a load by group interaction for postural tremor amplitude
caused by lower tremor amplitude in the ET group at 0% and 5% 1-RM compared to 15% and
25% 1-RM; load did not influence tremor amplitude in the CN group. There was a load by group
interaction for the measure of time-dependent structure. This interaction was caused by greater
time-dependent structure in the CN group between the 0% and 5% 1-RM loads and the 15% and
25% 1-RM; there was no load effect in the ET group. In ET subjects, total extensor EMG
spectral area (1-40Hz band) increased with each additional load, reflecting increased muscle
work. Interestingly, the percent of the total power accounted for by the tremor-related peak
declined incrementally at 5%, 15% and 25% 1-RM. Discussion: The key finding was that ET
postural tremor amplitude was greatest at lighter loads. Two factors likely contributed to this
finding. First, the EMG spectral peak caused by tremor became proportionally smaller at
increasing loads and thus less able to drive the wrist at the tremor frequency. Second,
preliminary analysis showed that synchronization of the tremor frequency with the mechanical
resonant frequency of the wrist joint, which was reduced with increasing load, was greatest at
0% and 5% 1-RM loads for most individuals in the ET group.
Disclosures: K.E. Norman , None; M.E. Heroux, None; N.J. Badke, None; G. Pari, None.
Poster
276. Voluntary Movement: Stroke, Damage, or Disease
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 276.12/KK22
Topic: D.17.a. Kinematics and muscle activity
Support: ONR Grant N00014-05-1-0844
NIH Grant R01 HD045639
Stanford University Bio-X Bioengineering Graduate Student Fellowship
NSF Grant BCS-0450218