It has been demonstrated that a long term stay in hypergravity (HG : 2G) modified the phenotype and the contractile properties of rat soleus muscle. This muscle became totally slow, which is a sign of anticipated ageing. Consequently, our aim was to determine if rats conceived, born and reared in hypergravity showed adaptative capacities in normogravity (NG : 1G). This study was performed on rats divided into two series : the first was reared in HG until 100 days and was submitted to normogravity until 115 to 220 postnatal days (HGNG rats); the second was made up of age paired groups reared in normogravity (NG rats). The contractile, morphological and phenotypical properties of soleus muscle were studied. Our results showed that the NG rats were characterized by coexpressions of slow and fast myosin, respectively 76.5 and 23.5 % at 115 days. During their postnatal maturation, the fast isoform was gradually replaced by slow myosin. At 220 days, the relative proportions were respectively 91.05 % and 8.95 %. From 115 to 220 days, the HG-NG rats expressed 100 % of slow myosin isoform and they presented a slower contractile behaviour comparatively to their age matched groups : at 115 days, the whole muscle contraction time was increased by 35 %, and by 15 % at 220 days. Our study underlined the importance of gravity in the muscular development and suggested the existence of critical periods in muscle phenotype installation.