NEW YORK — Deborah McGee’s legs started feeling weak a little before the halfway mark at Sunday’s New York City Marathon. Her breathing labored and her body ached. But it wasn’t enough to stop her.

After 25 competitive races, the marathon was McGee’s toughest challenge and her last.

McGee, 50, who is from Stafford County, was diagnosed last year with Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, which destroys the motor nerve cells that operate the muscles and leads to paralysis. For McGee, who said she loves the feeling of completing a marathon because it’s a distance not many can accomplish, Sunday’s race was a chance to experience the thrill of a competitive run one final time — before the disease spreads to her legs.

“The fact that I was able to do this was a gift,” said McGee, who crossed the finish line of the 26.2-mile marathon in five hours and 45 minutes with tears streaming down her face.