ISOMETRIC AND DYNAMIC EXERCISE STUDIED WITH ECHO-PLANAR MAGNETIC-RESONANCE-IMAGING (MRI)

Purpose: The effect of different types of exercise upon echo planar (E P) magnetic resonance (MR) images was examined during and after both d ynamic and isometric dorsi-flexion exercises at matched workloads and durations. Methods: Healthy untrained subjects performed either dynami c exercise through a full range of motion and against a constant resis tance or isometric exercise at the center of the range of motion and a gainst a constant resistance at 25 or 70% their measured maximum volun tary contraction (MVC). EP MR images were acquired at 1.5 T every 4 s before (4 images), during (27 images), and after (29-65 images) exerci se. A spin echo EP sequence was employed with TE = 30 ms. TR = 4000 ms , FOV = 20 x 40 cm. 64 x 128 matrix. The changes in proton transverse relaxation rate Delta R-2, [s(-1)]) relative to values obtained before exercise were calculated from individual images at different times du ring and after exercise. Results: At both 70 and 25% of MVC, the maxim um Delta R-2 after dynamic exercise (-8.38 +/- 0.32 s(-1) (70%), -6.47 +/- 1.23 s(-1) (25%)) was significantly greater (P less than or equal to 0.05) than after isometric exercise(-5.91 +/- 0.67 s(-1) (70%). -3 .80 +/- 0.87 s(-1) (25%)). Throughout the period that recovery was mon itored, the recovery patterns of Delta R-2 following isometric and dyn amic exercise at both workloads remained parallel. Conclusions: We con clude that exercise-induced changes in MR images are influenced not on ly by workload and exercise duration but also by the type of exercise, and we postulate that these differences result from the different phy siological responses elicited by the different types of exercise.