PLEASANTON -- Renea Cribbs narrowed her eyes and let out a low, slow breath of air as she dipped down into something called an "atomic push-up."
Legs suspended outward by elastic grips, she twisted her hips to the side before tucking her knees to her chest and lowering her body into a push-up.
It looked as brutal as it sounds.
The soft-spoken Texas native was in the midst of a rigorous "total body resistance exercise" -- also known as a TRX workout -- with Olympic swimmer and Bay Area native Natalie Coughlin at Pleasanton's 24-hour Fitness.
The TRX company, based in San Francisco, developed a method of fitness training where one's own body weight is used to stretch and strengthen multiple muscles and joints simultaneously.
Cribbs, 57, recently won a "Train With Natalie" competition hosted by the company that brought her from her home in North Richland Hills, Texas, to California for a mini-vacation and an Olympic-style workout.
Cribbs said she began using the TRX workout thanks to her son, Chad, who accompanied her on the trip. Chad was recently certified as a TRX trainer in Alabama.
"It's nice to have a trainer," Cribbs said as she took a water break. "I'm really getting some new ideas."
Coughlin took no mercy on Cribbs or her son during their two-hour long workout -- she gave them a workout similar to the one she uses to train for competitions.
After an hour, Cribbs and her son hit the pool where Coughlin gave them stroke and breathing tips -- and a little break from all the sweating.
"The water was actually relaxing," Cribbs said. "But I know I will be sore tomorrow."
For Coughlin, watching Cribbs and her son successfully complete a series of push-ups, crunches and core strengthening routines was impressive.
"They did a great job, and they will be sore, but that is a good thing," she said. "They earned their dinner. ... I don't know any woman in her mid-50s that is working out as hard as (Cribbs) did today."
While most do not consider working out a great way to spend a vacation, Cribbs said she truly enjoyed her time in California, especially her time at the gym.
"I felt a good burn," she said at one point during the exercise.
"You sure don't look like you do," Coughlin answered. "That's the sign of a good athlete. Someone who may be feeling it, but they don't show it."
Contact Katie Nelson at 925-847-2164 or follow her at Twitter.com/katienelson210.