Imagine zooming around the .875-mile track of Iowa Speedway.

Now imagine doing it with the force of 800 pounds pushing you sideways nearly the entire way for 250 laps.

Thats what it will be like for IndyCar drivers during the sixth running of the Iowa Corn Indy 250 on Saturday night.

Unseen to the casual race viewer is just how tough it is to drive an open-wheel machine at speeds between 110 and 140 miles per hour. While drivers are in a seated position for the races two-hour duration, theyre doing an immense amount of work. If its a hot day on the track, the toll it takes on the body and the mind is amplified.

At the start of the race, your heart rate is up and a lot of it is nerves. Even on the road courses, said 25-year-old Marco Andretti, winner of last years Iowa Corn Indy 250. After the first four laps, youre like, Theres no way Im making it to the end.

A lot of it is mental. Youre driving up on the wheel. Youre close to the people. Once the race strings out, you calm down and dont hold as much on the wheel. Its unbelievable how much further you can exert yourself.

A big part of what makes an IndyCar race so physically demanding is the G-force exerted on each driver. G-force, a term familiar to military jet pilots, is a measure of stress on a body during rapid acceleration. Its the same force one feels while spinning on a tilt-o-whirl. One G is the force of gravity, the weight you feel standing around. During the turns of an IndyCar race, that force is significantly multiplied.

At the Indianapolis 500, the average winning speeds are around 180 mph. In pole qualifying, speeds are in excess of 220. Andretti won last years race at Iowa Speedway with an average speed of 118.671 mph, while pole qualifying speeds are often in excess of 180.

Its in the turns that G-force comes into play. On a straightaway, drivers are at 1 G. They can relax a bit, check gauges and take time to breathe. Indianapolis Motor Speedway a 2.5-mile rectangular oval features long straightaways with seven to eight seconds between turns. Drivers feel forces greater than 1 G for 50 percent of the lap, and peak at 4 Gs.

But at Iowa Speedway, the only straight part of the track is a short portion of the 869-foot backstretch. Other than that, drivers are in a near-constant turn. Drivers feel more than 1 G of force for only 25 percent of the lap, but will consistently hit G-forces over 5. At 5 G, a 200-pound person is being pushed sideways at 1,000 pounds.

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Health, fitness are key for IndyCar drivers on and off the track