Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of fitness club operator Life Time Fitness (UNKNOWN:LTM.DL) plummeted 21% today after its preliminary fourth-quarter results and outlook disappointed Wall Street.

So what: Life Time shares have risen over the past few months on optimism over a rebound in memberships, but today's preliminary fourth-quarter results -- EPS of $0.53 to $0.56 versus the consensus of $0.65 -- coupled with downbeat guidance for 2013 naturally squashes that hope. In fact, Life Time experienced higher-than-expected membership acquisition costs during the quarter in addition to the lower-than-expected membership growth, forcing analysts to recalibrate their growth expectations considerably.

Now what: Management now expects 2013 EPS of $2.85 to $2.95 on revenue of $1.2 billion to $1.22 billion, below the consensus of $3.17 and $1.24 billion. "The Company's preliminary guidance includes the anticipated impact of the timing of 2013 new center openings, pre-sale expenses for centers opening in early 2014 and the investment in growth initiatives," wrote Life Time in a statement. So while the beaten-down stock might be tempting for short-term traders to pounce on, Life Time's still-shaky financial and competitive position make it a highly questionable long-term opportunity.

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