When the US economy emerged from the recession in June 2009, productivity was rising at a fast clip. Companies had spent the downturn cutting jobs and were lean and efficient. But as the recovery has chugged on, productivity growth has stalled, averaging less than 1% a year since 2011. Although there are many reasons for the productivity rut, one of the primary ones is that businesses aren't investing in their workers. Business investment fell almost 25% during the recession and hasn't come back the way many economists had expected, especially given that low interest rates make borrowing less expensive. It's not as if companies don't have money to spend. Cash on corporate balance sheets has increased almost 70% over the past four years to more than $2 trillion, the size of Russia's economy. Profits are high, and employee compensation as a percentage of GDP fell to a 65-year low last year, according to the BEA.