What do Shaquille O'Neal and Jane Fonda have in common? Osteoarthritis in their knees. 

And they're joined by millions of fellow Americans. Knee osteoarthritis accounts for more than 80% of the 58.5 million cases of arthritis in the U.S., affecting at least 19% of American adults 45 and older.

That's why it's important for research to explore how — short of knee replacement — you can best reduce the pain and retain mobility.

A randomized, controlled study in the Annals of Internal Medicine looked at whether three weekly treatments for 12 weeks of a shorter "low-dose" or longer "high-dose" exercise routine reduced pain and increased function.

What the researchers discovered was that while a high-dose routine (each treatment lasted 80-90 minutes) did have better results in the first six months, the advantages faded after that. In the long run, the low-dose routine of 25 to 30 minutes per session was just as beneficial.

But the high-dose routine did have one big disadvantage: Far more people dropped out of it than the low-dose one.

If you're struggling with chronic knee pain from osteoarthritis but don't have the stamina or time for longer exercise therapy sessions, don't feel guilty.

Here are two other knee-sparing tips:

• A study in the journal Arthritis & Rheumatology found that among people with knee osteoarthritis and intermittent pain, walking for exercise decreased their odds of new and frequent knee pain by 40%.

• There's a beneficial supplement routine that's osteoarthritis-modifying; check it out in "The Great Age Reboot."