Our guest blogger today is Dr. Phillip Gardiner of the University of Manitoba Faculty of Kinesiology and Recreation Management. Phil is just completing a term as the interim Scientific Director of the CIHR Institute of Musculoskeletal Health and Arthritis.
A recent dinner conversation with Phil included a discussion of the neurological changes that occur with increased physical exercise. I suggested that exercise may increase the number of neuromuscular junctions which would in turn activate more motor units and improve muscle performance. Phil mentioned that his research at the University of Manitoba showed that it was more than that. In fact, increased physical activity can also improve the function of individual neurons.
I was fascinated and immediately asked Phil if he would write a blog entry for ‘Explorations in Health Research’. Here is an account of Phil’s explorations in exercise physiology.
I have always been intrigued by the adaptations that occur in our physiological systems when we increase, and also decrease, our daily physical activity levels. This curiosity began with my involvement as an athlete, and an intercollegiate swimming coach (of the University of Alberta Golden Bears, 1976-8).
I decided early in my scientific career that I would search for the biological mechanisms that bring about these adaptations. Mechanistic research of this nature can have a wide array of practical applications, not only in the field of human performance in general, but also in the areas of rehabilitation, aging, and the prevention and treatment of chronic disease.
Although our knowledge of what happens to the heart, circulatory system, bones, and muscles when they are exposed to regular increases or decreases in activation is good, little is known about how the nervous system responds to these challenges. During the past 12 years, my laboratory has been conducting a unique research program, concentrating on the large motoneurons in the rat spinal cord that innervate and control the activation of muscle fibers.
When exposed to periods of increased activation, such as regular physical activity, these neurons change the expressions of genes controlling their ion channels and receptors, so that they become more excitable, and more responsive to command signals coming from limb receptors and higher nervous centers. Alternately, during reduced activity such as one sees during prolonged periods in space, these neurons lose excitability.
My laboratory has also reported changes in metabolism, morphology, and the effectiveness of neuron-neuron contact of these neurons with decreased activity. When neurons are affected, the complex circuits in which they participate, and which are involved in all of our complex movements, also function less effectively. Thus, prolonged periods of decreased activity and/or sedentary behaviour render these neurons and circuits more difficult to recruit and use effectively. Athletes, on the other hand, appear to have more excitable and finely-tuned neurons and neural circuits which can be brought into use with less effort.
Taken together, our results demonstrate that spinal nerves and nerve circuits are responsive to changes in physical activity levels, in ways that render them more or less effective in generating, transmitting, and performing motor acts. While these results are from motoneurons and spinal circuits, the mechanisms may be the same for other neuron types. Thus, the “use it or lose it” idea, involving changes in effectiveness of neuronal function, most likely relates not only to motor functions, but also to sensory, autonomic, and cognitive functions.
Photo 1 : micrograph of a spinal motoneuron, with visible dendrites stretching out to contact other cells, and a cell nucleus in the center. Photo taken by Jeremy Chopek, doctoral student in Dr. Gardiner’s lab.
Photo 2 : members of the Gardiner lab, for a “wear your worst hat” photo.