The objectives were to study both the contribution to orthostatic intolerance (OI) of calf venous volume during a stand-test, and the effects of a combined eccentric-concentric resistance exercise counter-measure on both vein response to orthostatic test and OI, after 90-day head down bed-rest (HDT). The subjects consisted of a control group (Co-gr, n=9) and an exercise counter-measure group (CM-gr, n=9). Calf volume and vein cross-sectional area (CSA) were assessed by plethysmography and echography during pre- and post-HDT stand-tests. From supine to standing (post-HDT), the tibial and muscular vein CSA increased significantly in intolerant subjects (tibial vein: +122 % from pre-HDT, muscular vein: +145 %, p<0.05) whereas it did not in tolerant subjects. Intolerant subjects tended to have a higher increase in calf filling volume than tolerant subjects, in both sitting and standing positions. The counter-measure did not reduce OI. Absolute calf volume decreased similarly in both groups. Tibial and Gastronemius vein CSA at rest did not change during HDT in either group. During the post-HDT stand-test, the calf filling volume increased more in the CM-gr than in the Co-gr both in the sitting (+1.3 ± 5.1 %, vs -7.3 ± 4.3 %, p< 0.05) and the standing positions (+56.1 ± 23.7 % vs +1.6 ± 9.6 %, p<0.05). The volume ejected by the muscle venous pump increased only in the CM-gr (+38.3 ± 21.8 %). This study showed that intolerant subjects had a higher increase in vein CSA in the standing position and a tendency to present a higher calf filling volume in the sitting and standing positions. It also showed that a combined eccentric-concentric resistance exercise counter-measure had no effects on either post-HDT OI or on the venous parameters related to it.