“We know that health is considered the greatest wildcard—it’s the No. 1 key to a happy retirement, and the biggest worry,” said Ken Dychtwald, Age Wave CEO. “Physical—and fiscal—fitness turn out the be the best retirement investments.”

Americans are also willing to work longer: Three quarters of the respondents said that they would take a part-time job after retirement to help shore up their savings; 43 percent said they would be willing to work full-time. Two-thirds of the respondents, 67 percent, said they would be open to learning new skills to be able to work in a different position or industry.

According to Dychtwald, the results show that Americans are thinking about retirement preparation as more than saving and investing.

“It wasn’t simply a matter of ‘what’s their number?’ and ‘do they have savings?’ They were imagining different ways they’d get there,” said Dychtwald. “With the aging of the baby boomers, we’re likely to see a proliferation of a range of course corrections.”

Other adjustments included cutting back on charitable donations, which 77 percent of respondents felt comfortable with, downsizing a house, acceptable to 75 percent of respondents, and moving to a less expensive location, named by 67 percent of respondents.

Even more Americans, 90 percent, said that they would be willing to cut back on their living expenses to fund a financially secure retirement, while 79 percent said they would seek out financial advice.

Twenty-four percent even said they're considering driving for Uber or Lyft, said Dychtwald. “One in four were willing to rent out a room on a short-term basis,” he added.

Yet the statistics on retirement readiness remain grim. While most respondents say they want to live to the age of 90, 27 percent of them only feel prepared to fund 10 years of retirement.

The survey suggests U.S. pre-retirees are coming to grips with the reality that retirement is a more daunting task than it was for their parents and grandparents, a Merrill Lynch executive said.

“A high percent graded themselves low on their financial readiness," Kevin Crain, head of workplace financial solutions for Bank of America Merrill Lynch. They also had a sense of reality about the serious course corrections they would need to make.”