The isometric twitch and tetanic contractions of three hindlimb muscles (soleus, plantaris, extensor digitorum longus) were recorded in situ in groups of mdx and C57BL/10 control mice at young, adult and old ages (3, 4, 6, 8, 13, 26, 39 and 52 weeks). Based on a two-way analysis of variance (age/phenotype) the mdx phenotype did not modify the absolute tension but was associated with a significant decrease in the tetanic tension normalized to muscle weight in all the muscles which became heavier. These results suggest that the contractile material in mdx is not so powerful as in controls. Moreover, significantly faster time to peak and half-relaxation time were observed in mdx soleus and plantaris. Comparison between these contraction characteristics and those of other experimental models suggests that the high percentage of regenerated fibres in mdx muscles could play a role in modifying contractile properties.