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In March 2001 I received the good news that my proposal for the ISB Student International Travel Award was approved. From that day onwards I could make definite plans for my visit to the Department of Physical Therapy at the University of Maryland in Baltimore, USA under the guidance of Professor Mary Rodgers.

After visiting the ISB conference in Zürich, I started my visit in the USA in August with attending the ASB conference in San Diego. It was a good experience to present my research project and to discuss it with my colleagues from other research groups.

The study I have performed in Baltimore is part of my Ph.D. project entitled “Manual wheelchair propulsion: biophysical aspects of learning”. A previous research project showed that during a 3-week wheelchair learning program the mechanical efficiency and the timing variables (i.e. push frequency, push time, cycle time) changed over time. No remarkable changes were seen in 3Dforce production. Besides or together with a possible influence of the timing variables on the mechanical efficiency other aspects of changing coordination in the learning process could be alterations in muscle activation and segment characteristics. The latter were not included in the initial experiment. Several studies were conducted to examine EMG patterns during wheelchair propulsion (Mulroy, 1996; Rodgers, 1994; Veeger, 1991) but, as far as known, alterations in muscle activity patterns over time due to learning has not been studied before. The shoulder-muscle complex offers a wide range of movements what might result in a great variability in repetitive movements of the upper extremity. One way to constrain this redundancy is to link muscles together into a muscle synergy. Bernstein (1967) proposed that, early in learning, redundancy might be constrained by freezing out degrees of freedom via muscle coactivity. Later in learning, these restrictions could be relaxed. One hypothesis that emerges from this idea is the following: muscle coactivity should decrease with skill learning as degrees of freedom are freed up and limb stiffness is reduced. T he purpose of the study, performed in Baltimore, was to examine adaptations in force application, kinematics and EMG patterns during a wheelchair-learning process.

To study the changes of these variables over time a cross-sectional study was conducted in which 10 totally inexperienced non-wheelchair-dependent subjects were compared with 10 experienced wheelchair-dependent subjects. Subjects of both groups had to propel a wheelchair simulator during three four-minute exercise blocks at a certain velocity and intensity. During those exercise blocks the forces and torques applied on the hand rim were measured as well as the kinematics and EMG patterns of the upper extremity and trunk. At the moment I am analyzing all the data. I am planning to submit an article about this research project in the summer of 2002.

Next to making use of the Baltimore expertise and experience as well as other measurement devices to answer our research question, it was also very nice to have the possibility to exchange ideas and to learn about different approaches to wheelchair experiments and research in general. Besides the experience in the lab, I also had a good time experiencing the American culture and participating in the American way of life, e.g. playing football for the first time in my life.

I would like to thank the ISB for giving me the opportunity to perform a research project in another lab and especially to meeting more researchers involved in the same research area. I am grateful to Dr. Mary Rodgers for giving me the possibility to work in her lab; and Dr. Kevin McQuade and Margaret Finley for their assistance in the lab and the enjoyable conversations about our research projects. I also owe many thanks to my advisors Dr. Luc van der Woude and Dr. DirkJan Veeger, both of whom encouraged me to go to the University of Maryland.

Sonja de Groot
Faculty of Human Movement Sciences
Vrije Universiteit, Amsterdam


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