Khov after reading this I did a little looking around and Satori is right, whippets with a single mutated gene are desired because they are extremely fast, if they have two mutated genes they become double muscled or "bully whippets" problem is that the heart and lungs do not increse in size so they are unable to provide enough oxygen to feed the muscles which leads to muscle cramps from excersise (since muscles cannot recover at a normal rate) as well as exceedingly short life expectancies due to the added stress on the heart.
"If you get hit and it hurts hit him back you not knocked out yet."-Joe Doerksen
The Toxic Terrors (FFL)
Demetrious Johnson*Eduardo Dantas*Rafael Silva*Zach Makovsky*Michael Page