Halah Alhamrani, 41, runs a gym for women called FlagBoxing -- its motto is Fight Like A Girl -- in the western Red Sea city of Jeddah, offering fitness classes such as callisthenics, CrossFit, boxing and kickboxing.
Relying on word-of-mouth publicity in a country where exercising in public is culturally deemed unbecoming for women, Alhamrani is working to empower a generation with little to no exposure to sports.
"On a daily basis, women who have never done sports walk into my class, some with their mothers," Alhamrani told AFP at her gym, which opened in 2016.
"They walk out more confident. Many find their voice. The mothers approach me and say: 'Thank you for offering such an empowering feeling'."
- Abayas left in the locker -
At first blush, the gym screams California, not Saudi Arabia.
Wearing headbands and workout attire, women are seen lifting weights, practising sparring techniques and pounding their fists into a punching bag.
Some of them crumple up their abaya gowns and toss them into a locker. They sweat it out over thumping music.
Around 150 women, including Saudis but also other Arabs, share a sense of camaraderie.
A note scribbled on a whiteboard reads: "I can't wait to come back!"
Another banner on the wall reads "BADASS".
"It sometimes feels like a tea party -- without the tea and cookies," Alhamrani jokes.
- 'My husband is unhappy' -
Women exercising in public were long a potential target for the kingdom's austere religious police, which has largely been neutered in recent years.
But dramatic social reforms sweeping Saudi Arabia, including a historic decree allowing women to drive from June, have shone the spotlight on figures such as Alhamrani who have long fought isolated battles for basic freedoms.
Under Crown Prince Mohammed bin Salman's Vision 2030 reform plan, the government is seeking to jump-start women's sports despite the risk of riling conservatives.
Only four Saudi women featured in the Rio Olympics in 2016 after two were named in the team for London in 2012 -- the first time the Gulf nation sent female athletes to the Games.
The kingdom has since then been granting more prestige to the idea, appointing prominent princess Reema bint Bandar to oversee women's sports in the kingdom in 2016.
- Low-profile -
The country is also moving toward compulsory physical education classes for girls after a ban was scrapped in 2014.
Alhamrani is involved in shaping the new public school sports curriculum.
As the daughter of an American mother and Saudi father, she enjoyed a privilege denied most Saudi girls, in that her parents were open-minded and encouraged sports from an early age.
That start has put her on track to become one of the kingdom's early pioneers of women's boxing training.
For now, her low-profile gym operates out of a residential complex, behind opaque glass walls with no outdoor signage.
The location is available on her website, but even so, some first-timers have to call to find their way.
- Gym as therapy -
Some clients view the gym sessions as therapy, Alhamrani said. It offers them such a release that she says some of them end up crying.
"I used to be a timid mother who could not look people in the eye," said a 36-year-old housewife and mother-of-four, and a regular at the gym.
"The gym gave me a voice that I had lost. It gave me strength that I never knew existed."
But Alhamrani says some women have dropped out after they began "expressing themselves boldly" in a way that sometimes makes male relatives feel threatened.
"My husband is unhappy", Alhamrani was told among the reasons.
Under the country's rigid guardianship system, a male family member -- normally the father, husband or brother -- must grant permission for a woman's study, travel and other activities.
Also holding back women's sports is an acute shortage of professional female athletes and coaches.
Women's gyms are slowly proliferating, but the idea of mixed gender sports remains taboo.
And some female professionals still caution against offending cultural sensibilities.
"Sports is empowerment," said Lina Almaeena, a member of the kingdom's advisory Shura Council, and director of Jeddah United, Saudi Arabia's first women's basketball team.
"We are not fighting for mixed gender, abaya-less sporting events. Our aim is not to go against our culture. Our goal is mass participation of women in sports."