Muscle biopsies were taken from soleus and vastus before and after a 60-day bed rest (BR) to examine expression changes in the regulatory proteins of the thin filament, and contractile function. Twenty-four women separated in 3 groups were submitted to BR, to combined protocol of resistance and aerobic exercises during BR (BR+Ex) or received a supplementation in amino acids during BR (BR+Nut). Ca²⁺-tension relationships were etablished in single skinned fibers identified by their MHC and TnC isoform expressions. Expression patterns of regulatory proteins were analyzed on muscle pieces. For both muscles, BR produced similar decreases in slow and fast fiber diameters but larger decreases in P₀ maximal forces in slow than in fast fibers. Specific forces were decreased in slow soleus and vastus fibers which displayed a reduction in Ca²⁺ affinity. These changes were accompanied by slow to fast transitions in regulatory proteins, TnC and TnT appearing as sensitive markers of unloading. Exercises prevented the changes in fiber diameters and forces and counteracted most of the slow to fast transitions. Nutrition program had a morphological beneficial effect on slow fibers. However, these fibers still presented decreases in specific P₀ after bed rest. Phenotypical transitions due to BR were not prevented by amino acids. Finally, in VL muscle, BR induced a decrease in <I>O</I>-glycosylation level which was prevented by exercise and attenuated by nutrition. In conclusion, this paper addressed for the first time in women the respective efficiencies of two countermeasures associated to BR on muscle properties and regulatory protein expressions.