I've compared some sports theme dolls

The full title of the playset is #7420 Olympic Gymnast Set for Barbie and PJ.
No, I don't understand the spinner either.

SunSet Malibu/Gold Medal PJ in her original swimsuit,
Free Moving PJ in #7424 Regatta on the Sea
and Ballerina Barbie in #9658 Mix N Match Set

This article is about two different but related topics:  three similar gym outfits, and the PJ Gymnast Set.

The first half pictures three outfits that are easy to confuse.  The 1975 Gold Medal Gymnast PJ original outfit, 1975's #7424 Regatta on the Sea, and 1976's #9658 Mix N Match Set.  The photo shows Gymnast PJ in part of her original outfit, Free Moving Barbie in Regatta and Ballerina Barbie in Mix N Match.  I don't own the gymnast bodysuit, just the Olympic swimsuits.  The difference is that the bodysuit has a high collar but the swimsuits have a regular open collar.  I also don't own the bikini pants to Mix N Match, so Barbie is wearing the yellow slacks from Regatta.

The second half features the PJ Olympic Gymnast Set.  You could get this set with or without PJ; I have the one without.  It is one of a few PJ gift sets sold over the years.  The front of the box is a photo of PJ performing and the back of the box shows some of the poses you could supposedly do.  I don't have the spinner thing, so I cannot tell you about it, but I do have the gauntlets (I guess that's what they are called) to hold the doll on the bar.

You have to put the gauntlets on the doll first, then slide them over the bar, then hang the bar on the towers.  It's almost impossible to put a doll in the gauntlets if you place them on the bar and tower first.  Getting the bar to slide between the gauntlets is difficult and you will have to forcibly bend the doll's thumbs or hands to complete the job.  The SunSet Malibu and Free Moving dolls of 1975 have different arm and hand arrangements and neither type of doll is easy to get onto the bar.  I also tried the 1976 Ballerina Barbie and her hands and arms don't allow the bar to slide in at all.

I couldn't get either a Free Moving or Malibu doll to do all of the poses on the box back; the dolls are simply too stiff, even with bendable legs and soft vinyl arms to get into position.  So I am demonstrating what I WAS able to do with the dolls.

Maybe the dolls were flexible enough to do these pose
in 1975, but they aren't now.

Hanging upside down is a good way
to straighten your back and clear your head

Barbie prepares to hang from her legs.

Next step is the hardest:
Sliding the horizontal bar past the hands.

PJ looks ready to do chin-ups!

I guess the horizontal bar could also be used as a dumbbell?

Halloween costumes through the decades

Although advertised as Western Barbie, the accessories don't resemble the doll's outfit.

The 1965 large size Skipper costume
is much longer than the shorter dress.

I believe this was a toddler girl's costume.

Note the non-PC "flame retarded" wording on the box.

I think this Barbie Bride outfit mask is a little creepy.
I think it looks like one of the Gabors!

The cuffs and bolo tie will fit an adult,
but not the rest of the Western Dress-Up Set.

A pink version of the Homecoming Queen Skipper gown.

The microphone is a nice touch for a beauty queen set.

I own six Barbie and Skipper Halloween costumes, two from the 1960s, one from the 1970s, Ione from the 1980s and two from the 1990s.  I bought one new at the store; the rest were purchased at garage sales or antique shows.
The first two were based on Skipper's Silk N Fancy dress, with extra gold trim on the bodice.  The trim is referred to as "Sparkle Velvet."  These were made by Collegeville Costumes/Collegeville Flag & Manufacturing Co. of Collegeville, PA.  It's the large, size 12-14 (whatever that means), for which I have the box and mask, and then the other dress that I suppose is a small.  The box is dated 1964, but I assume it was for sale in 1965.  Note that the Skipper mask wears a headband.
The next costume, also made by Collegeville, is on a hanger rather than in a box.  The wedding dress says "Barbie Bride," dated 1977, I assume for the 1978 market.   This was sold in conjunction with the 1978 Beautiful Bride Barbie.  The back is soft white vinyl while the front is rayon.  The dress has browned with age and I tried cleaning it but nothing removed the faded color.
Number three is one of the first items I purchased as an adult collector.  I was at a garage sale and found a box of accessories known as Western Barbie Dress Up Kit by H-G Industries Inc. of Long Beach, NY.  The box is dated 1981, the year Western Barbie was sold, but I suppose the items were sold in 1982.  The box was missing the cowboy hat and vest, but I have the bolo tie, chaps, belt and cuffs.
My first 1990s item is another Skipper outfit.  I bought this item new at Woolworth's.  It is all soft vinyl and you could probably lose 10 pounds while sweating when wearing it.  It's called "Teen Fun Skipper" made by Hasbro for Ben Cooper.  (How did Mattel's competitor Hasbro end up with the rights to a Skipper item?) . The hanger says "Tiny-Tot/(3-5)" but I don't know if that the size or recommended age.  It came with a molded mask and was probably one of the last outfits sold with a mask before stores stopped selling them.  The dress is Barbie pink and pictured on it is a 1989 Homecoming Queen Skipper in a pink version of her gown.
Last was another garage sale purchase called "Barbie Beauty Queen."  One of the tags on the satin cape is a 1990s Barbie clothing tag and the other says it was made by Arco Toys (a 1980s and 1990s subsidiary of Mattel).  It also came with a hairbow, brush and comb.  The thing with the fuzzball on it is a fake microphone with an on/off switch, but I don't know how to open it or make it work.  The tiara says "Mattel, Inc., 1996," so I assume it was sold in 1997.
There is a word on the Collegeville costumes which is now politically incorrect.  Today outfits would say "flame retardant."