The main role of in supporting physical activity is to serve as an antioxidant, protecting tissues from oxidation.â

I think the correct term to fill in the blank would be Vitamin E. The main role of Vitamin E in supporting physical activity is to serve as an antioxidant, protecting tissues from oxidation. This vitamin is an antioxidant and is important in having strong immunity and healthy skin. It acts a peroxyl radical scavenger which disables the production of free radicals in the tissues which are damaging to the body. It reacts with the free radical and forms a tocopheryl radical which is reduced by a hydrogen donor. Therefore, returning it to the reduced state. Free radicals are harmful to the cells, organs and the tissues. 

How they differently handle their team- hagrid a champion explains this better than me