Under Armour has come a long way from its roots in helping to popularize athletic performance apparel. The industry has become huge, and despite the emergence of many new players, Under Armour has not only held its own but also gone after Nike ( NKE -0.03% ) and its dominance of the athletic footwear market. With its Spine shoe brand, Under Armour will expand beyond shoes for niche sports to tackle the much larger running-shoe market.