Is the US economy running out of gas?

Is there another U.S. recession on the way?

That's a question rattling investors, worrying business leaders and shaping the debate on the presidential campaign trail.

The answer depends a lot on how you measure the strength and durability of the recovery, now in its seventh year based the business cycle dates tracked by economists at the National Bureau of Economic Research.

"There is always some chance of recession in any year," Fed Chair Janet Yellen told Senators on Thursday. "But the evidence suggests that expansions don't die of old age."

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To see how this recovery compares, CNBC tracked a series of economic and market data over the last eight recessions since 1960 — starting each cycle with the beginning of each downturn.

By just about every measure, the current expansion has been the weakest of the eight.

One of the main reasons has been the relatively sluggish pace of spending an investment — by consumers, government and businesses — since the Great Recession began in December 2007. Consumer spending has recovered far more slowly than past recoveries. And despite a massive stimulus program in 2010, government spending at all levels is actually lower than when the Great Recession hit.

Consumers have been slow to spend, in part, because their paychecks have been rising more slowly than in past downturns. While the job market has recovered and the pace hiring sped up in the last two years, the overall gains in employment lag past recoveries because the scale of job losses in 2007 and 2008 was much higher.

Consumer spending — which makes up about two-thirds of the U.S. economy — has also been held back by the sharp drop in household wealth that accompanied the collapse of the financial markets. To rebuild the trillions of dollars in lost wealth, American households have been stashing more into savings than in past recoveries.

Corporations have also struggled to keep profits moving ahead after the crash of 2007. While profits have recovered along with the job and housing markets, the gains lag all but the 1981-1990 cycle, when the U.S. entered a relatively mild recession brought on by a downturn in the housing market. That cycle was followed by the Roaring '90s, when a surge in profits and the rapid growth of the technology industry sparked the Internet stock market bubble.

By comparison, the latest cycle has produced relatively weak stock market gains — outpacing only the mid-'70s expansion, when rampant inflation eroded stock market gains when measured in real terms.