THOMPSON, L.V., D.A. LOWE, D.A. FERRINGTON, and D.D. THOMAS, Electron paramagnetic resonance: a high-resolution tool for muscle physiology. Exerc. Sport Sci. Rev., Vol. 29, No. 1, pp 3-6, 2001. Skeletal muscle function can be altered by changes in protein structure and motion. Electron paramagnetic resonance (EPR) paired with site-directed spin labeling has been used to study the relationships between (a) muscle force and myosin structure and (b) muscle relaxation and Ca-ATPase motion and structure.