Some stocks are one-hit wonders, making a big splash when they first appear, then quickly fizzling into obscurity or oblivion. But for other stocks, that initial big move is only a preview for even bigger and better gains to come.

Today, we've listed three stocks that made some of the biggest upward moves over the past month, which we'll pair with the ratings issued by our Motley Fool CAPS community. The higher each stock's rating, the greater CAPS members' faith in that company's ability to keep on beating the market.

Stock

1-Month  Change^

CAPS Rating
(out of 5)

Amarin (Nasdaq: AMRN) 116.4% **
Hansen Medical (Nasdaq: HNSN) 71.4% ***
American Apparel (NYSE: APP) 68.1% **

Source: FinViz.com.
^From March 24 to April 25.

While you were out, the market plunged below the 12,000 level and soared back up, so before we get shaken out again, let's see why the CAPS community thinks some of these companies might continue to outperform the market.

A mighty temblor
There was nothing fishy about the results Amarin reeled in with its clinical trials for a fish oil therapy to lower triglyceride levels without raising "bad" LDL cholesterol. That it also met its endpoints for safety sets it apart from rival treatments from GlaxoSmithKline (NYSE: GSK), whose Lovaza can raise "bad" cholesterol in some patients.

It's been nearly a billion-dollar business for Glaxo, and that's probably the real reason behind investors casting the net so far for Amarin's stock. It will be looking to take a large chunk of that business.

With 86% of the CAPS members rating the biotech believing it will outperform the broad market averages, you can let us know on the Amarin CAPS page or in the comments section below whether there's still time to fish or cut bait.

Secure in the knowledge
After popping higher in February following a deal with Philips Electronics, medical device maker Hansen Medical did it again earlier this month by submitting a premarket notification application to the FDA for its vascular robotic system and catheter. Building upon its current Sensei-X technology, the Sensei robotic platform translates the surgeon's hand motions into device movement.

Hansen is looking to grow its revenues in the robotic space that has served Intuitive Surgical (Nasdaq: ISRG), Accuray (Nasdaq: ARAY), and Varian Medical (NYSE: VAR) so well. However, while each of these companies has limited competition for their specialized technology, thus giving them a wide field to profit from, it requires that they're able to keep growing sales by persuading ever-greater numbers of customers to buy. In instances like this past recession, they can be hard to come by.

CAPS member mdriver78 says the situation is even more difficult for Hansen because it doesn't have approval yet. It enjoyed a big spike in price because it submitted its application, but that's not the same as getting regulatory permission:

In the US, the Vascular Robotic System is not available for sale pending clearance of the 510(k) submission, which is currently under review. In Europe, the System requires CE mark and is not available for sale, nor can it be marketed until the CE mark is received. This type of news spike generally decays back to previous run pricing in relatively short order.

Add Hansen Medical to the Fool's free portfolio tracker to see if the plans for this device win regulators' hearts.

Should I stay or go?
The term "loose cannon" derives from the damage heavy iron cannons could inflict on ships if they were not secured on a storm-tossed sea. It's a fairly apt description of American Apparel CEO Dov Charney, who appears to go to great lengths to wreak havoc on his company by means of his personal peccadilloes.

Financial shenanigans have gone hand in hand with the CEO publicly calling his CFO "a loser" without credibility in the industry. It's been sued by a former accountant; its independent auditor, Deloitte & Touche, resigned; and it reappointed the auditor who was terminated just prior to Deloitte coming on board. Oh, and then there are the sexual harassment lawsuits Charney's been named in and the creepy nature of the company's advertising.

It's anyone's guess why Great White North, a Canadian private equity firm, agreed to funnel up to $43 million into American Apparel to help it stave off bankruptcy.

While it wasn't possible to foresee the possibility of someone actually wanting to keep the retailer afloat, CAPS All-Star ksiu1 highlights some reasons why it's likely it will only have thrown good money away:

Cash flow is tight. Since they're in violation of the debt covenants with Bank of America they're pretty much at their mercy. If BofA doesn't roll over their credit facility APP won't have enough cash to pay any bills. Even if APP extends this they're going to have limitations on how they spend it and that will put a crimp on APP expanding their retail presence.

Surprisingly, 83% of CAPS members rating the stock see it beating the indexes, but the low two-star rating suggests they think there are better places for your money. Let us know your thoughts on its future on the American Apparel CAPS page and don't forget to add it to the Fool's free portfolio tracker.

Shake, rattle, and roll
With these stocks shaking the market this past month it pays to start your own research on them at Motley Fool CAPS. Read a company's financial reports, scrutinize key data and charts, and examine the comments your fellow investors have made, all from a stock's CAPS page.

Intuitive Surgical is a Motley Fool Rule Breakers choice. GlaxoSmithKline is a Motley Fool Global Gains recommendation. The Fool owns shares of Bank of America and GlaxoSmithKline. 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.

Fool contributor Rich Duprey does not have a financial position in any of the stocks mentioned in this article. You can see his holdings here. You can shake, rattle, and roll The Motley Fool's disclosure policy, but it still won't break.