Exercise TVaining-Induced Changes in Skeletal Muscle Microvasculature Assessed by Contrast Enhanced Ultrasound

Abstract

Contrast-enhanced ultrasound (CEU) can non-invasively quantify microvascular volume, blood velocity, and flow in tissue accessible to ultrasound. Changes in microvascular properties in skeletal muscle that occur longitudinally with a given intervention have not been documented with this technique. PURPOSE: To examine the effects of intensity of exercise training on skeletal muscle microvasculature in abdominally obese individuals with the metabolic syndrome. METHODS: We studied 27 abdominally obese adults with metabolic syndrome [20 F, 7 M, mean (SD) age 46.4 (9.8) yr, ht 169 (9.7) cm, wt 100.5 (19.2) kg] by CEU before and after a controlled, randomized exercise training intervention. Subjects' right foot flexors (gastrocnemius and soleus) were imaged to quantify microvascular properties at rest and during pedal ergometry. Subjects were randomized to one of three groups for 16 weeks: control (C), low-intensity aerobic training (LI), or high-intensity aerobic training (HI). Baseline comparisons between rest and exercise were made using pooled data by paired t-tests. Training responses using difference scores were analyzed by ANOVA. RESULTS: At baseline, acute pedal ergometry at 0.2 Hz resulted in significant increases from rest in: muscle microvascular volume (0.31 +/−0.2vs. 2.6+/−1.7 arbitrary units (a.u.); p < 0.001), erythrocyte velocity (0.09+/−0.04 vs. 0.11 +/−0.04 a.u.;p = 0.03), and microvascular flow (0.028+/−0.02 vs. 0.265 +/−0.16 a.u.; p < 0.001). Exercise training increased microvascular volume and flow both at rest (volume change: C = −0.008, LI = +0.23, HI = +0.28; flow change: C = −+0.0003, LI = +0.01, HI = +0.03) and during pedal exercise (volume change: C = +1.1, LI =+0.9, HI = +2.4; flow change: C = +0.0006, LI = +0.1, HI = +0.33), with the increase in flow during pedal exercise in the high-intensity training group significantly greater than control (p for ANOVA = 0.04). The degree of individual changes in microvascular properties did not correlate strongly with changes in abdominal visceral fat, maximal aerobic capacity, or insulin sensitivity assessed by QUICKI. CONCLUSION: We conclude that exercise training increases skeletal muscle microvascular volume and flow in an intensity dependent manner, and that these changes are independent of other variables associated with metabolic syndrome.