Former recruitment consultant Helen Smith, 35, led the circuits-style workout, which included jumping-jacks, sit-ups, push-ups and partner work.
The hour-long class, which costs £8, is described as "gentle boot-camp style exercise with partner games and teamwork" suitable for all fitness levels.
People aged between 33 and 70-years-old took part in the first class in Southampton, Hants., but Helen welcomes adults of all ages to try the activity.
Helen, who is a member of naturist organisation British Naturism, said: "The main benefit of exercising n3ked is that you can really see what the instructor is doing in the exercises.
"For example, if you are doing a plank but wearing baggy exercise clothes, it is hard to tell if you have the correct form or not.
"You also don't have to think about washing sweaty gym clothes after the class, and it's a great way to celebrate the body."
"I think people are starting to embrace naturism more and more.
"It's interesting, because in this day and age you have on one hand pop-stars wearing scantily-clad clothing, and that being seen as quite sexual behaviour, and on the other hand you have things like naked bike rides.
She added: "Participants are required to pre-register by emailing me, and to show ID at the beginning of the class, just for everyone's peace of mind.
"Nothing untoward happens in these classes, and if there was any hint of that then the person responsible would be asked to leave."
"The idea behind naturism is that it is your natural body, and there is nothing sexual about it."
Nude-ercise classes will soon take place in London and across the south east.