Biomedical Engineering Reference
In-Depth Information
walking, but no significant change has been observed in normalized hip, knee or
ankle moments. Weight loss not only induces a simple mass-related adaptation in
gait, but also mechanical plasticity in the gait strategy.
1 Introduction
Walking is a planned but highly autonomous motor activity. During walking,
changes in the vertical position of the body's center of mass control the gravita-
tional potential energy of the body, and are accompanied by opposite changes in the
kinetic energy of the body. This results in a pendulum-like mode of movement that
saves mechanical energy. At the optimal walking speed, recovery of the energy of
the body, by exchanging potential and kinetic energies, is maximal [
38
]. The neural
networks in the brain stem and spinal cord, such as the central pattern generators,
autonomously coordinate locomotion [
13
]. However, the appropriate peripheral
afferent feedback from the skin, joint receptors, and from muscle spindles and Golgi
tendon organs is essential for human locomotion. Moreover, the central nervous
system, including the motor cortex, cerebellum, brain stem, vestibular system and
vision, also has an important role in controlling human locomotion [
55
].
Simulation results based on mechanical models of the articulated system,
experimental accelerometer measurements, as well as direct in vivo recordings
suggest that considerable joint loads and stresses arise during locomotion [
3
]. The
loading transmitted to the hip or knee joints during walking depends on the phase
(swing/stance) of the walking cycle, on the walking speed as well as on the
inclination (level/up/down) and quality (soft/hard) of the surface [
3
]. Maximum
loads on the knee and hip joints during level walking arise after heel strike, i.e.,
when weight transfer from one foot to the other occurs. Typically, based on
mechanical modeling of the lower limbs and by utilizing inverse dynamics,
computational maximum hip joint forces during slow (1.1 m/s) or normal (1.5 m/
s) walking are 3-4 times the body weight (BW), and may momentarily reach 7 BW
during rapid (2.0 m/s) walking [
3
,
41
]. In the knee joint, the maximum tibio-
femoral force is also about 3 BW during normal walking [
3
,
41
]. However,
interindividual differences in walking style can create considerable variation in
peak loads [
3
,
50
].
In 2008, more than 1.4 billion adults aged 20 years and older were overweight
(body mass index (BMI) 25.0-29.9 kg/m
2
), and of these about 500 million were
obese (BMI C 30.0 kg/m
2
)[
62
]. Overweight and obesity are the fifth leading risk
factors for global deaths, and a raised BMI is a major risk factor for diseases such
as cardiovascular diseases, diabetes, musculoskeletal disorder and some cancers
[
62
]. Obesity also has a major influence on health-related quality of life and on
many essential physical activities of daily living such as walking ability, aerobic
capacity and muscle strength [
31
]. However, there is still comparatively little
detailed
information
regarding
the
basic
characteristics
of
the
obese
gait,
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