The Influence of Vestibular and Muscle-Tendon Capacities on Locomotor Stability, Plasticity and Falls Incidence

Humans over 50 years old are at an increased falls risk and deficiencies in
dynamic gait stability can be observed as early as 40 years of age. Dynamic
gait stability refers to the ability to control one*s center of mass
appropriately during motion so that forward progress during walking or running
continues without the loss of balance in any direction. Falls most commonly
occur during walking and are often attributed to age-related neuromuscular
deficiencies, for example reduced muscle strength, power and leg muscle
asymmetry and a slower reaction time to perturbations. Walking is a complex
motor task, which requires frequent adjustments of body and limb positions. Two
important sets of systems in humans are those that assess and process the
external environment (the sensory systems) and those that produce the required
movements for the given external environment (the musculoskeletal systems). If
the systems that control these adjustments do not function normally, falls can
be a likely outcome. For older people, the injury risk and the threat to
quality of life that falls present are of great concern. Aside from the injury
risk to individuals, fall occurrence is a major concern for European countries
with growing elderly populations, due to the associated healthcare demands of
falls. The physical, psychological and potentially financial harm that can be
caused by falls represent valid reasons for a detailed study of the underlying
contributing factors.
The ability to react and take a large, balance recovery step following
perturbations (such as a trip, slip or stumble) is a key factor in recovering
from mechanical perturbations. However, recovery stepping responses are
diminished in older subjects and vestibular disorder patients. That being said,
locomotor adaptation to repetitive locomotor tasks has been shown in a number
of subject groups and therefore, targeted physical exercise or other types of
interventions to reduce falls risk and improve the plasticity of locomotion in
these subject groups are of importance. Adaptation to external gait
perturbations is not currently well understood. The observed differences
between healthy subjects and those with mild neuromuscular deficiencies in
association with ageing and more severe neurological disorders such as
vestibulopathy are relatively recent and the extent to which the adaptation and
plasticity of human gait is influenced by neuromuscular factors has not been
thoroughly analyzed. Therefore, the challenging and perturbing conditions that
can be provided by the CAREN system (Motek Medical, Amsterdam), lend themselves
well to answering these questions.

Primary Objective:
• To determine the adaptation potential of the reactive stepping response
following repeated mechanical perturbations while walking.
Secondary Objective(s):
• To determine and compare the initial recovery response to a mechanical
perturbation while walking in healthy young and older adults.
• To analyze the magnitude of limb to limb transfer and retention over time of
adaptations in the reactive stepping response to mechanical perturbations while
walking in healthy subjects.
• To determine how biomechanical features of non-perturbed, normal walking
affect stability control of gait both during walking and during recovery from
perturbations.
• To determine how performance on the locomotor plasticity assessment protocol
(Adaptation potential, limb to limb transfer of adaptations, initial recovery
response) is related to fall incidence and fear of falling in older subjects
over a 1 year period.

Setting: University Hospital Maastricht:
CAREN Measurements: CAREN Lab, Dept of Physical Therapy
Type: Observational, cross-sectional study
The groups will consist of a healthy young group, a healthy older group.

In general, there is very little risk associated with participation in this
study. Some minor muscle soreness may be experienced for a few days following
the muscle-tendon assessments and a dizziness sensation may be experienced
during the clinical vestibular assessments but this will be made clear to the
subjects before obtaining informed consent. Given the potential benefits
discussed above of this research to these at-risk groups, these small chances
of acute discomfort are considered negligible.