Lift & Carry : Whats The Best Way To Gain Muscle To Be Able To Lift And Carry 50 Pounds?

Whats the best way to gain muscle to be able to lift and carry 50 pounds? - lift & carry :

Must to wear 50 pounds of my work. I have to address the situation, a long distance. Now I can easily lift and carry around 35 pounds for any distance. What is a safe and effective way to can increase the weight and distance to do something. So, I'm a girl (if not already) an opinion of what I want to make sure that still gives me the strength I is not great big muscles!