In addition to altitude sickness, there are many factors that can contribute to nausea and vomiting while running and many runners suffer the consequences during marathons and ultra-marathons even where altitude is not an issue. High altitude can contribute to these problems.

* Dehydration--When you are running hard (up Pike's Peak at any speed is hard) it is often tough to drink enough fluids. This is compounded by any preexisting condition.

v. intr.  mild dehydration. If you had just traveled to the race, you may have been a little dry before it even started. The altitude also contributes to dehydration since the humidity is so low.

* Low glycogen glycogen  (gl?`k?j?n) , starchlike polysaccharide (see carbohydrate) that is found in the liver and muscles of humans and the higher animals and in the cells of the lower animals.  stores--Sugar is the fuel that makes the body go. When this runs low, your body will use other sources, such as fat for energy, but it still needs glycogen to prime the pump. 

* Altitude--Even if you are running at what would be an easy pace on a flat road at sea level, this may be an intense pace going uphill at altitude. At greater intensity, blood is shunted from the gastrointestinal tract gastrointestinal tract
n.
The part of the digestive system consisting of the stomach, small intestine, and large intestine.

Gastrointestinal tract   . Absorption will be slowed and nausea can be intense.

* Level of exertion--It is not uncommon to experience nausea during and after an intense workout.

* Low sodium--This is more likely to be a problem in ultra-endurance events, but you do want to make sure that you replace electrolytes along with carbohydrates and water

This is information on the web.....