i would suggest using multi-segment exercises (uses more than one joint) such as squats, presses, and pulls. i dont think density training, or any sort of strength/hypertrophy scheme would work as well with a single joint exercise such as curls. especially to strengthen your body proportionally for track. you probably have the rep scheme/concept down for density training, i just dont think your exercise selection is very good. you can look in the FAQ for exercise selection. i actually like the workout i am doing right now, which is bench press, squat, and pullups. i do that using the density concept.