hi. I am a 45 year old male. i have not been running in years. this past weekend, i ran a 5k race. had to walk a lot of it. i wasnt gasping for air and most of my body felt and worked great. however, after the first 1k, my legs just gave out. like they had no energy at all. i had to walk. then i would job a little more, then walk. in all, i probably ran less than half the race and walked the rest.
can anyone give me some suggestions to building the endurance in my legs, or what or why my legs just tire out so easily?