I've seen vids of Japanese ladies bouncing on these types of ball. Difference is, the Japanese version had a hard point dildo fixed to the top. Ladies bounce up and down and get pleasantly fucked by the dildo!
Balas
Prefershaved
The lady on the "yellow" ball, is giving her superb natural tits a better exercise workout than the other lady, who seems to be only just "juddering" hers!