Unit Laboratory
of physiology and biomechanics of locomotion
LIST OF THE NEW
RESEARCH PROJECTS IN THE FIELD OF LOCOMOTION
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Effect of exercise on the muscle and bone loss during extended weightlessness
The two principal physiological impediments to putting man
into space for prolonged periods of time are the loss of bone calcium,
and the loss of muscle mass. Even though the specific homeostatic mechanisms
involved in regulating bone and muscle mass are poorly understood at this
time, they are clearly dependent on the effects of gravity. Therefore these
homeostatic mechanisms can be treated as a ‘black box’ to control bone
and muscle loss in a zero gravity environment provided the cues (or a functional
subset of them) can be ‘tricked’ into believing they are in a ‘normal’
1 g environment. Available evidence would seem to indicate that the many
of the cues derive from the stress of supporting the body’s mass within
the acceleration of Earth’s gravity, but certainly not all. Some cues,
such as impact loading (bone) and work (muscle), may derive from the effects
of the body’s inertia, independent of gravity. The objective of this project
is to develop a compact instrumented treadmill that will allow us to duplicate
as nearly as possible the impact loading and muscular work involved in
‘normal’ locomotion that is independent of the specific subgravity level.
More information: Norman
Heglund
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The mechanism of locomotion of the elephant
Size changes everything in vertebrates. A squirrel can run
straight up, or straight down, with hardly any change in energy consumption
relative to running on the level at the same speed; yet a human, or a horse,
can only very laboriously manage much smaller inclines. Likewise, an ant
can carry many times its on body weight, a human can carry about two times
his weight, and a horse cannot even carry once again its weight. It seems
that large animals do not measure-up relative to small ones. This is, in
fact, logical. If we take a small animal and simply multiply all its dimensions
by, for example, four (roughly a dog to a horse), the strength of the bones
and the force generated by the muscles will increase about 16-times (proportional
to cross-section), but the weight of the animal will increase 64-times
(proportional to the volume). An inevitable consequence of size is that
larger animals are relatively more weak and fragile compared to small animals.
Large animals do, however, enjoy a metabolic 'economy of scale'. For example,
it costs an elephant only about 1/150th as much energy to move a gram of
body weight a unit distance.
The effect of body size on the physiology and biomechanics
of animals (allometry) has been extensively studied in animals ranging
from mouse to man. Other than horses (which, after centuries of selective
breeding are very likely atypical) very few data exist on large (>100 kg)
animals. Nevertheless it is clear that most allometric trends seen in the
0.01-100 kg size range cannot be extended to much larger animals. For example,
running speed certainly increases with size up to roughly 100 kg, but then
appears to decrease as size continues to increase. Similarly, the efficiency
of locomotion (specifically the efficiency of positive muscular work production)
increases from around 5% in a mouse to 70% or more in a 100 kg pony; no
efficiency data exist for larger animals, but certainly that trend cannot
continue indefinitely. Also, the safety factor in bone loading decreases
rapidly with increasing size, but its exact value has never been measured
in larger animals.
There is keen interest in good, quantitative biomechanical
and physiological data on large animals not only for understanding the
constraints on size-scaling in general, but also because of the direct
application to the study of dinosaurs. This study will be the first time
quantitative biomechanical and physiological data will be collected on
African elephants, the largest existing terrestrial animals.
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The control of the step frequency during running in children and in adults
The aim of this project is to investigate the importance of the stretch
reflex in the control of the step frequency during running and hopping
in place in children and in adults. This study integrates biomechanics
and neurophysiology of locomotion. The experimental setup is under construction.
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Responsable : Philippe
Gérard - Contact : pHg