Hi, I'm fifteen and I run xc and track. I'm 5'4 and 100 pounds, none of which is in my arms. I have alot of shoulder and upper-back soreness during longer runs/races. I also can\'t do a single push-up. A coach suggested that I look into some sort of weight training program to prevent this.
For a high school girl just looking for enough muscle tone to prevent upper-body fatigue from weakness, what would you suggest I use? Low weights with few reps? Or heavier weights with few reps? How often?