In vivo measurement of diffusion and pseudo-diffusion in skeletal muscle at rest and after exercise.

To investigate whether diffusion-related compartmentalization could be observed in skeletal muscle and whether this compartmentalization was affected by exercising, attenuation curves of signal against diffusion weighting were obtained in skeletal muscle of nine healthy volunteers at rest and after an exercise. Fifteen points were obtained for each diffusion curve with diffusion weightings ranging between approximately 0 and 560 x 10(6) s/m2. Data were fitted a biexponential model using three parameters to yield two apparent diffusion coefficients, a long one, ADCL, and a short one, ADCS, together with the fractional volume, fL, associated with the long one. At rest, values of parameters ADCL, ADCS, and fL were 46 x 10(-9) +/- 37 x 10(-9) m2/s, 1.74 x 10(-9) +/- 0.11 x 10(-9) m2/s, and 3.6 +/- 1.3%, respectively. After exercise, these values were 89 x 10(-9) +/- 37 x 10(-9) m2/s (p < .001 vs. rest), 1.94 x 10(-9) +/- 0.13 x 10(-9) m2/s (p < .001), and 5.2 +/- 1.3% (p < .05), respectively. These variations demonstrate significant changes in attenuation curves between rest and postexercise in skeletal muscle and may support an interpretation of the long and the short components in terms of a microvascular and an extra-microvascular compartments.