[Abstract Title]. - Society for Neuroscience

Poster
275. Posture: Kinematics and Muscle Activity
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 275.23/KK4
Topic: D.16.d. Kinematics and Muscle Activity
Support: FHS111199
IRND110830
Title: Age-related changes in the first step generated for balance recovery
Authors: *N. BUGNARIU MARHAO;
Sch. of Rehabil. Scie, Univ. of Ottawa, Ottawa, ON, Canada
Abstract: Regardless of the various factors that place a person at risk for falls, the execution of a
change in support strategy by generating a fast and accurate stepping reaction is critical to
prevent the fall. The control of stepping reactions is complex because it requires the initiation
and execution of a rapid sequence of movements involving both lower extremities. In addition,
step kinematics need to be adjusted to match the disturbance in terms of direction, amplitude and
constraints imposed by surrounding environment. The demands of controlling these complex
stepping reactions may create difficulties for older adults, due to age-related impairments in the
neural and musculoskeletal systems. When the first step generated in response to loss of balance
does not restore equilibrium, multiple later steps often emerge. This strategy may become a
further risk for falls in itself due to increased chances of limb collisions. The purpose of these
experiments were to determine: i) the characteristics of a first step that is successful for balance
recovery in terms of kinematics and muscle activity patterns and ii) the age-related changes
occurring in the first step generated for balance recovery.
The kinematic and electromyographic (EMG) responses to unpredictable translations of the
support surface in the anterior-posterior and medio-lateral directions were contrasted between
healthy young (18-35 years old, n=5) and old (>65 years old, n=5) adults. The platform
perturbations forced a stepping reaction by either starting to move unpredictably at peak velocity
of 5m/s and translate for 20 cm, or it oscillate ± 10 cm at a 0.5 Hz frequency and stop abruptly
after an unpredictable amount of time. All participants undergo a sensorimotor assessment of
foot sensitivity, ankle proprioception and lower limb muscle strength.
In comparison to young adults who recover their balance by taking one large, directionallyappropriate
step, older adults took multiple (2-3) smaller steps and they failed to produce the
anticipatory postural adjustments required before lifting and swinging the foot to make the step
in response to external perturbations. The sequence of muscle activation pattern for the first step