Steamier sex
Strong abs and lower-back muscles give you the stamina and strength required to make most of positions like Reverse Cowgirl and Wheelbarrow. But even more important: A smaller waistline means better blood flow. When you are overweight you tend to have significantly more artery-clogging plague, which decreases blood flow throughout the whole body. Researchers have found that increased blood flow in the pelvic region improves vaginal lubrication, sensitivity, arousal and sensation.

Fewer injuries
Researchers for the US army tracked the injuries of male and female soldiers during a year of field training in which they periodically performed the standard army fitness test of sit-ups, push-ups and a 3.2km run. Those who could crank out the most sit-ups were less likely to suffer from injuries.

Better health
Having a great stomach doesn’t guarantee you will never call in sick, but studies show that people with flat abs are 25 percent less likely to develop heart disease; 35 percent less likely to have a heart attack; 41 percent less likely to develop high-blood pressure; 40 percent less likely to develop kidney cancer; 60 percent less likely to develop gallstones and 14 percent less likely to develop osteoarthritis.

A longer life
A Canadian study of more than 8000 people over 13 years found that those with the weakest ab muscles had more than double the death rate of the people with the strongest mid-sections.