Nineteen-year-old Petri Alva’s favorite sprint-kayaking event is the 500 meter. “It’s just a fantastic race because it combines speed and endurance in a really challenging way,” he said. He laughed and added, “It’s about 90 seconds of all-out pain.” That’s the positive attitude shared by both Petri and his twenty-five-year-old brother, Zachary Alva. They are…