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We have recently shown that a previous unknown longitudinal movement and a corresponding longitudinal strain are present in the arterial wall. The objective of this study was to introduce and evaluate an improved method for measurement of the longitudinal movement as well as to show results from the first in vivo trial of measurement of the shear induced longitudinal elastic modulus of the arterial wall. The total mean difference in estimated displacement between the new and old algorithms was 1 Â¿m with a standard deviation of 76 Â¿m. The mean shear induced longitudinal elastic modulus was 95 Pa (SD 39), range 49-153. This indicates that the longitudinal elastic modulus of the inner layers of the arterial wall might be 1000 times lower than the values reported for exposed vessel walls in vitro. The unavoidable sources of inaccuracy present in our methods cannot justify such a large discrepancy. Possible explanations are discussed; based on differences between adopted approaches and on the presence of forces other than shear stress.