Hi im 29 5'4 1/2 and i weigh 51kg which i think is nearly 8 stone. I dont eat that much and i do think this hinders my performance sometimes. Its something i have to look at, eating more frequently, bigger amounts so i know im getting the right amounts of the right foods i.e protein for recovery, foods for energy
To be honest i would say that how much you weigh isnt really the issue but looking at having a varied diet with everything you need in it. If you run and eat a good diet then your body weight will plateau at where its should be . But if your diet isnt very good then in the long run your performance will not improve Hope that helps Hayley