I showed up in sneakers and sweats, prepared to join the exercise class that meets every Thursday morning in Canoga Park.
I expected lots of stretching, a few jumping jacks, an easy jog around the grassy field at Lanark Park. The lawn was lined with yoga mats and ringed with baby strollers. The students were mostly moms, some clad in denim pants and spangly tops.
How hard could this class be?
After a few minutes watching ladies maneuver 50-foot battle ropes and hoist 20-pound fitness balls, I decided not to embarrass myself. I put away my water bottle and pulled out my notebook.
I'd been invited by Cal State Northridge professor Steven Loy, whose kinesiology students run free boot-camp-style classes every week at Lanark and three other San Fernando Valley parks.
About 40 people showed up, including a retired physician who drove in from Topanga, a nanny who walked the loop pushing two baby strollers, a husband and wife looking for an alternative to the local gym, and a mother of four who outran her 20-year-old daughter.
"She kept telling me, 'Come on, keep up,'" said Jennifer Arias, a San Jose State student who's home for spring break. "I said, 'Go ahead, I'll keep up.' But I couldn't catch her."
Before Maria Arias began exercising last fall, she could run only a few steps without struggling to breathe. Now she is so gung-ho, Jennifer knows not to get in the way of her weekly fitness routine.
"I have only missed one class since it started in September," Maria told me. "And that was when I had to take her to the airport to go back to college.
"I told her next time she has to make a flight, choose a day when I don't work out."
The workout I watched was not for pushovers: an hour spent rotating among four stations, where participants ran, lifted weights and did cardio and calisthenics as kinesiology students moved among them — straightening a leg, supporting a back, lifting a sagging torso.
Many had never taken an exercise class. "It was very hard at first," said Yohanna Minas, 44, who had problems with her back and legs before joining the sessions. "Now it's easier to bend, and my back doesn't hurt so much."
For the harried moms, this is social hour. Some drop their children at school and hurry to the park. Others haul baby carriages as they move from weights, to ropes, to squats. "You see your friends, you bring your friends," Maria Arias said. "When I'm here, I feel so motivated by looking at other people."
To Loy, that feeling is the point. "We want them to see, and their children to see, that exercise is a way to feel better and live healthier lives."
The professor launched the program at one park four years ago, with dual goals: He wanted to create internships for kinesiology students and opportunities for exercise in low-income neighborhoods.
Recreation Park in San Fernando provided the equipment, and Loy provided the instructors. He named the program "100 Citizens" because the city was celebrating its 100th birthday. "I wanted to be clear that it wasn't for everybody," he said. "This was for the residents of San Fernando."
The class started small but grew each week. In 2012, it won a national award from Michelle Obama's "Let's Move" campaign. That made it easier for Loy to persuade other parks to let him set up shop.
"We started out using resistance bands and park benches," he recalled. "As people started actually liking to exercise, the park was able to generate revenue and buy equipment."
And residents who'd never been able to afford to go to a gym can now choose from yoga, water aerobics, Zumba, body sculpting, Spinning and, of course, boot camp.
Kinesiology is the study of the mechanics of body movement. Cal State Northridge has the state's largest program, with 2,300 students.
Once considered the province of college jocks and would-be PE teachers, kinesiology now is a growing field in a graying nation — a foundation for careers as varied as personal trainer and orthopedic surgeon.
Christopher Balam was about to graduate and hadn't decided on a career when he signed up to volunteer with "100 Citizens" three years ago.
"I assumed that I would probably get a job personal training right after [graduation] and go on from there," he said. "I didn't know what the blueprint for success was because I didn't know anyone who was in a position I wanted to be in."
Now he's working on his master's degree in exercise physiology. He's writing his dissertation on "100 Citizens." He plans to become a community college professor and develop corporate wellness programs.
Volunteering has given students like him a chance to pick the brains of graduate students, develop leadership skills and learn to accommodate individual quirks and needs.
They've learned enough Spanish to order their charges to pick up the pace, praise a perfectly executed push-up, remind them to breathe as they hoist heavy weights. They don't mind lying on the ground to model a move alongside a frustrated novice.
And they're certainly not bothered when a mom takes a break to tend to a fussy toddler. Those little ones posted on the sidelines might just be their clients down the line.