Journals of Gerontology Series A: Biological Sciences and Medical Sciences, Vol 51, Issue 1 M17-M22, Copyright © 1996 by The Gerontological Society of America
Changes in spinal reflexes preceding a voluntary movement in young and old adults
JR Burke and G Kamen
Department of Exercise Science, University of South Carolina, USA.
BACKGROUND. Age-related differences in spinal excitability during response
preparation were assessed by eliciting either a 50% H-reflex or an Achilles
tendon reflex preceding the onset of a right plantar flexion contraction in
20 young adults (23.1 +/- 1.64 yrs) and 20 old adults (68.5 +/- 5.53 yrs).
METHODS. On each simple reaction time trial, the test reflex was elicited
at a specific test interval during either the foreperiod or the response
period. The foreperiod test intervals were 500, 600, 700, 800, 900, and
1000 msec after the presentation of the warning stimulus. The response
period test intervals were 50, 100, 150, 200, 250, and 300 msec after the
presentation of the response stimulus. Control reflexes were randomly
elicited between the simple reaction time trials. RESULTS. Changes in
reflex excitability were not observed during the foreperiod in either age
group. During the response period, the percentage of H-reflex facilitation
as compared to control H-reflexes was similar for the young (68%) and the
old (61%) adults, but the magnitude of Achilles tendon reflex facilitation
with respect to control reflex responses was greater in the young adults
(74%) than in the old adults (38%). The time course of H- and tendon reflex
facilitation was delayed in the old group during the response period.
CONCLUSIONS. The results indicate that processes underlying the preparation
and generation of a motor response are similar in young and old adults.
However, these processes occur at a slower rate in old adults.
