[M]ice have reduced bone mass and forelimb muscle grip strength and we propose that these effects might be direct due to lack of 5α-reductase type 1 expression.

5α-reductase type 1 inactivated male mice have reduced bone mass and forelimb muscle grip strength and we propose that these effects might be direct due to lack of 5α-reductase type 1 expression in bone and muscle. In contrast, the increased cortical bone mass in female Srd5a1 −/− mice is an indirect effect caused by elevated circulating androgen levels, which in turn probably is a consequence of 5α-reductase type 1 expression being rate-limiting for androgen degradation in female mice.

—Reduced Bone Mass and Muscle Strength in Male 5α-Reductase Type 1 Inactivated Mice: PLoS One, January 2011