It is well known that exercise increases muscle blood flow and improve oxygen extraction, ultimately enhancing muscle oxygen supply. However, there is a large variation in oxygen extraction capacity (OEC) during exercise, which may be due to capillary transit time heterogeneity (CTTH). By means of a relatively newly developed technique, contrast enhanced ultrasound (CEUS), accurate measurements of these vascular parameters (OEC and CTTH) can presumably be obtained, both at rest and during exercise. The aim of this work is to attempt to evaluate in vivo changes of capillary flow patterns in response to graded handgrip muscle work in 10 healthy subjects by means of CEUS. Furthermore, it is also the aim to demonstrate that CTTH is associated to oxygen extraction during graded handgrip muscle work. As far as is known, it is the first time that the vascular parametric model has been applied to CEUS. In this work, it has been demonstrated that graded handgrip muscle work is associated with reduced CTTH and increased OEC (R2-value of 0,96).