Maybe you can't help it if you never make it to the gym. Researchers at the University of Missouri have found that genes may play a role in motivation to exercise, at least in rats.
Frank Booth and Michael Roberts placed rats in cages with running wheels, and measured the amount of time the rats spent on the wheel over six days. They bred the 26 top runners with each other and the 26 least active rats with each other, repeating this over 10 generations to create "super runner" rats and "couch potato" rats.
The most significant difference between these two lines of rats were not body composition or levels of energy-storing mitochondria in muscle cells, but genes. The researchers now plan to study the 36 identified genes that differed between the rats, which could play a role in their willingness to exercise.
Read more about the tyranny of fat in Your Fat has a Brain