The effect of inertial loading on wrist postural tremor in essential tremor.
OBJECTIVE
Determine the effect of inertial loading on the strength of motor unit entrainment and the synergistic/competitive interaction between central and mechanical reflex tremor components in subjects with essential tremor (ET).


METHODS
Twenty-three subjects with ET and 22 controls held their hand in an outstretched position while supporting sub-maximal loads (no-load, 5%, 15% and 25% 1-repetition maximum). Hand postural tremor and wrist extensor neuromuscular activity were recorded.


RESULTS
Inertial loading resulted in a reduction in postural tremor in all ET subjects. The largest reduction in tremor amplitude occurred between 5% and 15% loads, which was associated with spectral separation of the mechanical reflex and central tremor components in a large number of ET subjects. Despite an increase in overall neuromuscular activity with inertial loading, EMG tremor spectral power did not increase with loading.


CONCLUSIONS
The effect of inertial loading on postural tremor amplitude appears to be mediated in large part by its effect on the interaction between mechanical reflex and central tremor components. Also, ET is associated with a constant absolute level of motor unit entrainment.


CONCLUSIONS
The amplitude of postural tremor is dependent on both central and peripheral factors, with proportionally greater motor unit entrainment occurring at low contraction intensities.
Héroux
M E
ME
School of Rehabilitation Therapy, Queen's University, L.D. Acton Building, Ont., Canada, K7L 3N6. mheroux@interchange.ubc.ca
Pari
G
G
Norman
K E
KE
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D020329:Essential Tremor / Q000175:diagnosis / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009469:Neuromuscular Junction / Q000503:physiopathology; D011187:Posture / Q000502:physiology*; D011434:Proprioception / Q000502:physiology; D012018:Reflex / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology; D014953:Wrist / Q000503:physiopathology*; D014955:Wrist Joint / Q000294:innervation / Q000502:physiology