The objective was to quantify by echography the changes in Gastrocnemius, (Gast) and Posterior Tibial, (Tib) calf veins cross section area (CSA) and the superficial tissue thickness (STth) in response to lower body negative pressure (LBNP) after 60d head-down bed rest (HDBR). The 24 healthy women (25-40y), were divided into 3 groups: control (Con), exercise and LBNP (Ex-Lb), nutrition (Nut: protein). All underwent a LBNP (0 and 45mmHg) pre and day 55 HDBR. Subjects were identified as finisher (F) or non finisher (NF) of a 10 min tilt test after 60 d HDBR. There were no differences in resting Tib and Gast CSA on HDBR day 55 compared to pre-HDBR for the Ex-Lb, Con and Nut or the F groups; for NF Tib and Gast CSA were significantly smaller after HDBR. At LBNP - 45mmHg Tib and Gast CSAs were not different from pre HDBR in all groups (Ex-Lb, Co, Nut, F, NF). Percent change in CSA of both veins from rest to LBNP 45 was greater in the Con and Nut groups compared to Ex-Lb, and also NF compared to F. Likewise, the percent increase in STth from rest to - 45mmHg was higher after HDBR in the Con and Nut groups compared to Ex-Lb, as well as NF compared to F. These results showed that the Ex-Lb minimized the bed rest effect on leg vein and tissue capacitance, while Nut had no effect, and that higher leg vein and superficial tissue capacitance were associated with reduced orthostatic tolerance.