Vomiting is not normal during exercise. If done under hot conditions, this may be a sign of HRI. Vomiting occurs because the gastrointestinal tract is no longer working properly and the ingested fluids are not absorbed. Vomiting increases an athlete's dehydration level and alters the balance of electrolytes.
You should assume that an athlete who vomits, especially during the first few days of practice, to have HRI and is at risk for heat stroke.
An athlete should never be returned to practice the same day vomiting occurs. They should be evaluated by a athletic trainer or physician before returning to practice.