Richard Simmons Quarantine Comeback, Helping People Workout

Richard Simmons is helping people struggling through these days of self-isolation -- an area of expertise for him -- by making a comeback of sorts ... strictly online.

The beloved, former fitness mogul has been out of the public eye since February 2014, but 3 weeks ago his YouTube channel began posting for the first time in 6 years ... right around the time Americans began getting ordered to stay inside to stop the spread of coronavirus.

The material is nothing new -- it's old 'Signature Moves' clips, workouts and motivational messages -- but sources close to Simmons tell TMZ ... the revival is due to fans clamoring for him to return and lead them through at-home exercise routines again.

The need for this doesn't get much greater than during a pandemic ... so we're told Richard's team obliged with the new video posts.

Our sources say Simmons' team is also working on a new line of licensed products to be released later this year. It's unclear exactly what it will include, but in 2018 he released a calendar and some classic exercise merch ... so maybe something similar.

Remember, Richard hasn't been physically seen since we got a partial glimpse of him returning home from the hospital in April 2017 ... and there's only been Bigfoot-esque sightings of him for years before that.

So the mystery -- and it's a big mystery -- where is Richard?  He's not in the videos, which are year's old.  Cops did a few welfare checks several years ago and said he was ok, but why isn't he at least introducing the videos?

We're told despite the flurry of Richard's YouTube vids, he's still not decided when or if he'll make a return to the spotlight ... but the recent activity is giving his fans hope.