Now some economists think a rebound could be on the way. For most of the recovery, wage growth has been anemic, suggesting companies faced relatively little pressure to invest in automation or to find other ways to squeeze more production out of workers. But as the labor market tightens, companies’ incentives could be changing.

“You could meet demand for a while by hiring workers, but with the unemployment rate at 3.8 percent, eventually you’re going to run out of easy-to-find workers,” said John G. Fernald, an economist at the Federal Reserve Bank of San Francisco and an expert on productivity. “Because workers have other opportunities, you end up having to pay them. And once you see wages going up, you say, ‘We have to become more productive to cover our costs.’”

That cycle could already be underway. Wage growth has crept up over the past two years. One measure preferred by many economists, the Employment Cost Index, posted its strongest year-over-year growth since the recession in the first three months of the year. And there are other indications that companies are struggling to find workers. Applications for disability insurance, for example, have begun to fall, a sign that companies may be more willing to look outside the standard labor pool to find employees. And while productivity has yet to rebound, corporate investment — historically a prelude to productivity growth — has been rising.

David Maletto, who runs a small packaging company in Eau Claire, Wis., said it had become increasingly difficult to find workers with the local unemployment rate below 3 percent. The company, which specializes in putting together variety packs of beers for Miller and other brewers, has had a particularly hard time holding on to unskilled laborers, who pack bottles into boxes and load them onto pallets. Turnover at those positions is constant, Mr. Maletto said, and the workers he finds to fill vacancies are often unreliable, showing up late, playing on their phones while on the clock or sometimes not showing up at all.