NMR relaxation times of skeletal muscle: Dependence on fiber type and diet

Skeletal muscles are composed of a mixture of different types of muscle fibers. Previous NMR studies of muscle have typically used muscles of mixed fiber composition and have not taken into account factors such as the dietary history of the experimental animal. In this paper we present evidence that the T₁ and T₂ relaxation times of two of the major types of skeletal muscle fiber are not significantly different under normal conditions. Following dietary manipulation of the rabbits (limiting potassium intake or increasing cholesterol consumption), the T₁ and T₂ relaxation times of psoas and soleus muscles were significantly different. The change in relaxation times of psoas muscles following dietary manipulation can be only partially explained by shifts in muscle water content. The results suggest that changes in diet are capable of inducing changes in water bonding and structuring in muscle tissues. Our results indicate that diet must be added to the growing list of environmental factors that can cause NMR contrast changes. Also, NMR measurements of muscles rich in one fiber type or another could be of value for detecting changes in body composition.