Abstract
While perturbation training is known to be effective in reducing fall
risk, it is unclear whether the interval of perturbations affects motor
response. We investigate postural responses that could vary with the
interval of perturbations, probably leading to different contributions
of relevant learning substrates. A total of 12 male volunteers with no
neurological deficits (age: 33.33±3.12 S.D.) experienced two sequences
of perturbations. Two sequences of perturbations were designed and
administered in turn: the first sequence consisted of 24-time repeated
perturbations with an interval of 5 seconds, while the second sequence
consisted of ones with an interval of 2.5 seconds. A perturbation of a
smaller magnitude was inserted into each sequence as a catch trial.
Perturbations were given by a force plate moving in the
anterior-posterior direction. The magnitude of the excursions of the
center of pressure (COP) and ankle angle in response to perturbations
with a longer interval is greater in comparison to that with a shorter
interval (P < 0.05). A difference in responses to the
perturbation following the catch trial appears in COP (P <
0.05), not in ankle angle (P > 0.05). These results suggest
that while contraction of agonist muscles and co-contraction of
antagonistic muscle pairs across the ankle joint for stability operate
independently of each other, the refinement of the neuromotor system for
a newly trained response can be modulated with stimulus intervals. The
dependency of postural responses on the interval could imply that the
strength of the learning effect varies with stimulus intervals.