Acne can be caused by a lack of zinc, among other things. Zinc is used in muscle repair and growth and for release of energy. If you training hard you may be using up so much zinc that your skin doesn't have enougth, causing the acne.
You can try supplementing zinc or eat more eggs, nut, wholewheat grain, rye, oats, or ginger root, all of which contain resonable quantities of zinc.
Other sings of zinc deficiency include poor sense of taste or smell, white marks on more than two fingernails, frequent infecitions, stretch maarks, low fertility, pale skin, tendency for depression, loss of appetite. If you have any/some/all of these as well it's almost certainly a zinc defeciency.