AMHERST, Mass. - Researcher Priscilla Clarkson of the exercise science department has seen many muscles at work at the Totman Gym at the University of Massachusetts, but now, thanks to cutting-edge technology, she can examine them in a whole new light. Clarkson is the principal investigator for a three-year, multi-university study of the role of genotype, or genetic makeup, in the development of muscles in the upper arm. The project involves five other public universities and one hospital, and it is funded by the National Institute of Neurological Disorders and Stroke, one of the National Institutes of Health (NIH). Eric Hoffman, of the Children''s National Medical Center in Washington, D.C., is clinical director.