Interesting, the mutation does not provide an evolutionary advantage in the wild. Appears the increased muscle generates less force and is more susceptible to damage. Twice the mass = half the strength (53% specifically). Explains why nature and breeders of functional working animals don't breed for it eg working dogs and horses but breeders of food animals eg pigs and cows do breed for it.
Results from
PNAS | Mobile
"Decreased Specific Force Generation in the Myostatin Knockout Mouse.
To examine the relationship between muscle size and improved function in
Mstn−/− mice, we first performed a series of tests of force generation. The maximal isometric twitch force (
Pt) and tetanic force (
Po) of extensor digitorum longus (EDL) muscles of 7-month-old male
Mstn−/− and age-matched C57BL/6 wild-type mice are presented in
Table 1 and
Fig. 1. Maximal
Po was reached at 100 Hz in both
Mstn−/−and C57BL/6 wild-type muscles and did not increase with stimulation at higher frequencies. We therefore compared values obtained at 100 Hz from wild-type and
Mstn−/− mice (
Fig. 1 a and
b). Despite the increased muscle bulk in the myostatin-deficient animals, maximal
Powas similar to that of wild-type mice of the same genetic background (
P = 0.189;
Table 1;
Fig. 1 c and
e). Moreover, when maximal
Po was normalized for muscle weight (specific force), we found that
Mstn−/−male mice generated only 53% of the force developed by wild-type animals (
P < 0.001;
Table 1;
Fig. 1d). Similarly, normalization of
Po for the cross-sectional area also revealed a reduction in specific force generation"