While Fools should generally take the opinion of Wall Street with a grain of salt, it's not a bad idea to take a closer look at particularly stock-shaking upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of Under Armour (NYSE:UAA) closed up 4% yesterday after J.P. Morgan upgraded the athletic apparel company from underweight to neutral.

So what: Along with the upgrade, analyst Matthew Boss boosted his price target on the stock to $77 per share (from $55), representing about 7% worth of downside to where the stock sits now. While Boss believes that Under Armour's margins and profit upside will remain pressured by heavy infrastructure investments, he thinks that several factors should continue to drive strong top-line growth.

Now what: Although Boss still leans toward Nike as his preferred play in the space, Under Armour's juicy growth opportunities shouldn't be overlooked.

"Given brand relevance, we believe ongoing product innovation (Charged Cotton technology created a $200M new business in two years), growth in footwear (every 1% of market share in just the running category represents an incremental $60M), growth in non-traditional distribution (department and specialty stores), and investments in the women's business (representing 29% of sales today) should continue to drive sales growth in North America (94% of sales)," Boss wrote. "At only 6% overseas exposure, global expansion is a large opportunity with specialty door expansion an untapped growth vehicle over time."

Of course, with the stock hitting a new 52-week high yesterday and trading at a lofty forward P/E of 45, much of that potential may already be baked into the valuation.

Fool contributor Brian Pacampara has no position in any stocks mentioned. The Motley Fool recommends Nike and Under Armour. The Motley Fool owns shares of Nike and Under Armour. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.