In this study, researchers compared the effects of pre- and post-natal food deprivation on the relative proportion of fiber types and contractile responses in the extensor digitorum longus (EDL) muscle of female and male rats at different post-natal ages.

EDL muscles from undernourished male rats showed a higher proportion of Type IIB than IIA fibers and larger normalized twitch responses (with respect to muscle weight) than those of control males. In contrast, EDL muscles from control female and undernourished female rats showed no significant differences in their fiber type composition and normalized twitch forces at most of the ages analyzed. Data are indicative that the EDL muscles from undernourished males are more susceptible to the effects exerted by low food income than the EDL muscles from female rats.

It is proposed that changes in the reactive oxygen species concentration and hormonal factors, due to undernutrition, are involved in the alterations observed in the fiber type composition and force production of EDL muscles in undernourished male rats and that estrogens may have an antioxidant protective role on the undernourished EDL muscles in female rats.

Source: J. Pereyra-Venegas et al., 2015. Effects provoked by chronic undernourishment on the fiber type composition and contractility of fast muscles in male and female developing rats. JAPAN online, October 2015. doi: 10.1111/jpn.12274.