: +32 10 47.44.32
Fax : +32 10 47.31.06
E-mail : Patrick.Willems@loco.ucl.ac.be
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The principal domain of research of our lab is the physiology and the biomechanics of terrestrial locomotion. Movement in sports (particularly in gymnastic) are also studied.
- Studies on terrestrial locomotion
At first glance, there are many different modes of terrestrial locomotion: some vertebrates move on Earth on two legs while others use four. They walk, amble, trot, pace, canter, gallop, hop, etc. In fact, this huge variety of locomotory types are all based on two basic mechanisms:
More information : Norman HEGLUND
- A force platform made of 10 plates (total length: 6 m.) measures the vertical and forward components of the ground reaction force during several walking or running steps. This platform is installed at the level in the middle of a 40 m long corridor.
- A of 16 plates (size of each plate: 1m x 1m) is under construction. This platform measures the ground reaction forces in the three directions of the space. It has a resolution of 3 N and a full scale of 50.000 N
- A piezo-electric force platform (KIESTLER®) measures the ground reaction forces in the three directions of the space.
- A motion analysis system with infrared cameras (SELSPOT®) records the movements of the body segments at 400 frames/s.Electromyographs (EMG) record the electrical activity of height muscular groups.
- A telemetric system allows to measure energy expenditure during various exercises (KOSMED K4®).
Main research projects of the last five years
- The mechanics of walking and running in children during growth
Three children run on the 6 m long force platform of the lab.
The aim of this study is to understand:
(1) how the mechanisms of locomotion change during growth,
(2) which are the factors that influence this evolution (change in morphology, increase of the weight and the size, maturation of the nervous system, modification of the muscular force...).
Three studies were realized these last years.
The energy expenditure in children during walking.
In this study, we measured the oxygen
consumption during walking at different speeds in adults and in 3 to
12 years old children.
work done by children during walking at different speeds
The mechanical work can be divided into different parts: (1) the external work necessary to sustain the displacement of the center of mass of the body relative to the surroundings, (2) the internal work done to accelerate the body segments relative to the center of mass of the body and (3) the internal work done during the double contact phase of walking by the back leg which generates energy that will be absorbed by the front leg (see picture). This last part is not counted in the 'classic' measurements of the positive muscular work done during walking. Using force platforms, we studied the effect of speed and age (size) on the internal work done by one leg against the other. We also measured the total mechanical work done during walking at different speeds in adults and in 3-12 years old children (paper in preparation).
The bouncing mechanism of running in children
The natural frequency of the body bouncing
system depends on the body mass and the stiffness of the elastic structures
responsible for the rebound. Between the age of initiation of running and
adulthood, body mass increases more than five times, but the effect of
growth on stiffness is unknown. In this study, we investigated the factors
affecting the freely chosen step frequency, and measured the mechanical
work done to move the center of mass of the body during running at various
speeds in children of different age.
- Mechanics and energetics of human locomotion on sand
The mechanics and energetics of locomotion have been thoroughly investigated only in the laboratory on hard, level, non-slippery surfaces, although these bear little resemblance to those actually occurring in nature. It could be that the energy-saving mechanisms utilized during locomotion on a hard surface are not functional on a soft surface, or that the muscles on a soft surface are in a condition such that they contract and do work at lower efficiency, or simply that the mechanical work required to walk or run on a soft surface is much greater since the foot does work on the substratum. The purpose of the present study was to quantify the increase in metabolic cost and the reason for that increase, in human walking and running on dry sand. A 50 m track containing 8 tons of sand was build (left picture). In order to evaluate muscular work during sand locomotion, a track was also build on the top of the force plate (right picture).
- Physiology of load carrying
Services to Society
People in the Third World often carry prodigious loads supported by their heads. With the exception of African women, virtually nothing is known about the energetics and mechanics of carrying head supported loads.
In Nepal, load carrying is mostly done by humans. Porters use a bag (doko) supported by a strap on the head (naamlo). On the average, loads are equal to body weight (occasionally up to two times the body weight). We studied the energetics (oxygen consumption - right picture) and mechanics (mechanical work - left picture) of Sherpa carrying head supported loads in an effort to determine if this is a particularly economical means of portage, and if so, what mechanisms are used to minimize cost.
- Effect of gravity on the mechanics of walking and running
Professor Cavagna (University of Milan) walking at 0.4 g (like on Mars).
The aim of this study is to understand how gravity affects the mechanisms of locomotion. We measured the ground reaction forces during walking in reduced (0.4 g) or enhanced (1.5 g) gravity and during running in enhanced gravity (1.3 g). Hypo-gravity is obtained during parabolic flights while hyper-gravity is obtained during circular flights
- List of the new research projects in the field of locomotion
- Effect of exercise on the muscle and bone loss during extended weightlessness
- Mechanics of locomotion of the elephant
- Control of step frequency during running in children and in adults
- Analysis of movement in gymnastics
In a first project, we analyze the movement of the center of mass of the body during a stationary backwards flip (see picture). This exercise requires one to take off and land at the same place. The aim of the work is to understand how the subject is able to induce a movement of rotation of the body without inducing a horizontal translation of its center of mass. We record the ground reaction forces and compute the trajectory of center of mass during that exercise (paper in preparation).
- Publications of the heigt last years
- Scientific Award
- B. SCHEPENS : Award of the Société de Biomécanique for the best Ph.D. these presented
at the congress of Montreal: The mechanics of running in children.
LAward of the Human Frontier Science Program 2000- 2001, 2001-2022 & 2002-2003
H.H. Jasper Fund 1999-2000, One year Fellowship, Canada
- M. PENTA : Award for the best poster of the 2nd World Congress of the International Society of Physical Rehabilitation Medicine, Prague, 2003
Responsable : Philippe Gérard - Contact : pHg