How do you gain weight if you're a runner?

If you are a runner looking to gain muscle mass then you want a lifting program that takes a minimal amount of time (so that it doesn't interfere with your running) and gradually increases resistance. Gradually increasing the workouts will force your muscles to adapt by adding strength and mass. Also make sure that you are eating wholesome and nutritious meals high in protein, complex carbohydrates, and healthy fats in order to support your exercise program.