By 2018, 24 percent of US workers will be 55 or older. Getty Images.

Fifty-year-old Debbie Germer has been a machinist at the Harley-Davidson's Motorcycle Plant in Menomenee Falls, Wis., for the past 12 years.

It is a hard, physically demanding work, especially for older workers.

"Some of that stuff - like the spine rolls - weigh 60 pounds. And you have to lift that up into a machine," Germer said.

Last September, Germer partially tore a tendon in her shoulder. Now, twice a week, before her work shift, she gets physical therapy at her work site. And twice a week she works out at a gym, also located at her work site.

The 1,000 assembly plant workers can drop by before or after their shifts, or even on their breaks, to work out at work.

It's part of an effort by Harley-Davidson to get their employees to shape up so it's less likely they'll break down.

Workers over 50 are more vulnerable than younger workers to injuries that keep them out of work - sometimes permanently.

"I guess the fitter you are, not just the longer you can work, the less chance of hurting yourself," Germer said.

If a worker does suffer a strain or sprain, there's medical aid from a doctor, nurse or physical therapist on-site.

When asked if workers last longer (to put it bluntly) when they're physically fit, John Lowry, General Manager of Powertrain Operations at Harley-Davidson, responded, "If you get a debilitating injury that could be the end of your career. So if we can stay out in front of those injuries or make sure they don't happen, then we can prolong a person's employment indefinitely."

Duke Energy in North Car0lina takes a similar approach.

All 2,000 of its line technicians begin each work day stretching.  The aim is to prevent soft-tissue injuries like strained and pulled muscles.

At Duke Electric, more than half of their line technicians are over 50- and replacing an experienced worker is difficult. It takes up to eight years to fully train someone for the job.

"These are very valuable folks and we want to keep them working as long as we can - for our benefit and for theirs," said Jim Stanley, senior VP of Duke Energy.

Both Duke Energy and Harley-Davidson believe their fitness programs are paying dividends: both report declining numbers of injuries, fewer lost work days and older, more experienced, workers working longer.