BALTIMORE (Map, News) - What a week for Under Armour and company shareholders.

The Baltimore-based athletic performance apparel developer reported significant income and revenue increases in the second quarter, while shareholders saw Under Armour’s stock price reach historic highs.

Second-quarter net income increased 136 percent to $5.7 million, net revenues increased 51 percent to $120.5 million, the company reported on Tuesday.

Under Armour announced second-quarter results the same day the Dow Jones industrial average tumbled 146 points over mortgage-firm troubles and oil-price surges. Wall Street was apparently impressed with Under Armour that day, however, as the company’s stock price increased 11 percent amid the turmoil.

Shares of the company traded at an all-time high of $66 on Wednesday.

“The second quarter marked significant milestones for us as we execute our plan against our key growth drivers,” Kevin A. Plank, chairman and chief executive officer of Under Armour, said in a statement.

Men’s, women’s and youth apparel revenues increased 53 percent in the second quarter. Footwear revenues, benefiting from the increased sales of football cleats, rose 29 percent to $20.1 million for the quarter.

“Under Armour is a growth company,” Plank said in a statement, “We are committed to executing on our plan to deliver value to our customers, retail partners and shareholders alike.”

Under Armour appears poised to take on some of its biggest competitors, including Nike, announcing this week it will release a cross-training shoe for jogging and court sports next summer.

The Baltimore company grew tremendously since it began developing sweat-fighting T-shirts 10 years ago. Under Armour has been a leader in the performance-apparel segment, which has grown nearly sixfold since 2001, according to Brady Lemos, a Morningstar analyst.

Under Armour might struggle to compete against Nike, Lemos said, because Nike poured almost $2 billion into advertising in fiscal 2007 — about 40 times more than Under Armour’s marketing budget.

“While the firm has plenty of room to expand into new categories like footwear, battling a host of entrenched competitors should prove challenging,” Lemos wrote in his report on Under Armour on Tuesday.

“Competition should only intensify now that Under Armour has entered the athletic footwear market.”

Shares of Under Armour ended Thursday trading at $62, down $2.13 or 3.32 percent.

acannarsa@baltimoreexaminer.com