Last week was another rough one for the S&P 500, as the index fell 0.7% to 1.066.19. Sovereign debt concerns in Europe took center stage again, masking a downtick in the unemployment rate. Uncertainty -- and therefore volatility -- is back as apprehension abounds.

Pops and drops
Here are the five biggest S&P 500 upticks and five biggest S&P 500 drops of last week (measured Friday close to Friday close):

Winners on the week:

Company

Percentage Gain on the Week

Airgas (NYSE:ARG)

44%

Lexmark International (NYSE:LXK)

25%

Cummins (NYSE:CMI)

12%

Starwood Hotels (NYSE:HOT)

10%

Broadcom

10%

Source: Capital IQ (a division of Standard & Poor's).

Losers on the week:

Company

Percentage Loss on the Week

Gannet (NYSE:GCI)

(16%)

MasterCard (NYSE:MA)

(12%)

Western Union (NYSE:WU)

(11%)

Marshall & Ilsley

(10%)

NRG Energy

(10%)

Source: Capital IQ (a division of Standard & Poor's).

A closer look
The market is always an expectations game. MasterCard reported a 23% jump in its fourth-quarter profit, yet earnings missed analysts' forecasts, which -- coupled with signs of decreasing credit use -- sent shares plunging lower last week. Results were buoyed by an increase in processed transactions and improvement in spending. However, higher operating expenses coupled with rebates and incentives caused profits to come in lower than analysts had expected. Results showed that consumers are relying on credit cards less and debit cards more. MasterCard says it anticipates a challenging first half of the year, but noted that it's optimistic about economic recovery in the second half.

On the flip side, engine maker Cummins reported better-than-expected fourth-quarter profits. Demand from emerging markets like Brazil and China drove earnings. The company said it also saw an increase in demand for on-highway truck engines in North America, thanks to new emissions standards that were invoked this year. Sales shot up 34% in the quarter, yet earnings and sales were down for the full year in 2009. In a reality check, Cummins said that the global economic downturn isn't behind us, and cautioned that the first half of this year would be as difficult as the first half of 2009. That's sobering news from a trucking parts company, which serves as a proxy for economic activity in the U.S. Notice, too, that results were driven by demand from outside the U.S. in emerging markets.

Also notice how both companies, which operate in very different industries, anticipate a difficult first half of 2010. The recovery is still weak, folks.

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Fool contributor Jennifer Schonberger does not own shares of any of the companies mentioned in this article. You can follow her on Twitter. Western Union is a Motley Fool Inside Value pick and a Motley Fool Stock Advisor selection. Motley Fool Options has recommended a write puts position on Western Union. The Motley Fool has a disclosure policy.