Why is it that my upper arms (and sometimes my fore arms) get so tired during races. I have run about five 10K- and a few 5K races now and still it seems to be the part of my body that suffers the most. I work on my arms for at least 4 hours in week in the gym. What else should I do. Can it be that I should rather change the heavier weights for lighter ones? Faster, consequent reps?