Big Frame Without Big Muscles

No matter what I do I find it hard to build my leg muscles. Stil, I’m not a smaller than average man in that I am 6ft1.5in", broader shoulders than av man, and I weigh a couple of pounds under 13 stones. (Carl Lewis was also same hieght as me and he was about 2 pounds lighter than me at 12st 8 or 12st 10.) Niether was he spectacular in the weights room when he was arssed to go in the gym.
I’m wondering, is one of the reasons for weight training for a sprinter to increase bodyweight slightly? I’ve heard that before although it would seem to slightly contradict the power to weigth ratio thing. If body size/weight is part of the reason then atleast I’ve allready got the big frame (for a runner), part sorted out/ that’s just my genetics.
But I’ve pretty much given up on hypertrophy emphases becuase it aint happeing despite the slightly more than 1 g protein per pound of bodyweight eating habits and despite the weights work. My upper body would get top heavy if I bothered to train it much so i don’t do much to my upper frame. My legs have a problem building cross sectional mass. Anyone in a simmilar situation who still got faster without increasing cross sectional mass in thighs/hips and without putting up impressive numbers in the gym? :frowning: