Obesity may mean your muscles are less able to cope with your body weight....

or as the headline says:  obesity creates wimpy rats

"These results may explain why muscle strength and locomotion are impaired in obese humans, and hence perhaps why it is so difficult to lose excess weight and recover from obesity," said Schilder.

The researchers first demonstrated that troponin T expression varied with body weight during normal growth. Then they artificially increased the body weight of one group of rats by 30 percent using a custom-made weighted vest. Externally applied weight caused a shift in the muscle troponin T expression, matching that of animals whose actual body weight was 30 percent higher. In contrast, troponin T expression did not respond to a similar increase in body weight in the obese rats.