The only significant difference between the two programs was a greater maximum bench press weight for the circuit-trained women.
But this finding, along with some trends toward differences in other parameters, suggest interesting contrasts, researcher Paige Wessel, from West Kentucky University in Bowling Green, told Medscape Medical News.
"With circuit training, strength improved more," said Wessell, who trains using a CrossFit program. But if you want endurance, "I'd say do CrossFit."
Wessel and three of her colleagues from West Kentucky University presented findings from four separate posters here at the American College of Sports Medicine 62nd Annual Meeting.
CrossFit has become popular in recent years, but few scientific studies have examined its effects on fitness. Wessel and her colleagues could find none that compared it with older circuit-training programs.
In both CrossFit and circuit training, participants complete a series of movements, particularly weightlifting and bodyweight exercises, in rapid succession.
CrossFit draws from gymnastics, power lifting, and other disciplines, and provides variety, with different modes, loads, and duration for each workout. Often participants complete the workouts as quickly as possible, emphasizing power, or the ability to move a load quickly.
Circuit training is a fitness approach that involves a specific work-to-rest ratio and emphasizes cardiovascular health and strength, or the ability to move a large load. Resistance loads are frequently lighter than in CrossFit in later stages.
To compare the two, Wessell and her colleagues recruited 23 active women who had not previously used either training method. The average age of the study participants was 29 years.
They randomly assigned nine women to CrossFit and 14 women to circuit training.
Both groups trained 3 days a week for 10 weeks. The CrossFit women used the company's Workout of the Day, and the circuit-trained women used a program designed by a researcher.
Improvements in a variety of parameters were seen in both groups over the study period.
There were no significant differences in bone mineral density between the two groups.
In the circuit-trained women, there was an increase in body mass, although percent body fat remained the same. This suggests that these women gained muscle.
Although this finding was not statistically significant, the researchers speculate that it could account for a greater increase in upper body strength in the circuit-trained women.
Because CrossFit participants typically don't practice the bench press and don't do much resistance training at the beginning of the program, improvements in strength, power, and agility could be attributed to "neuro-muscular adaptations," the researchers report.
Larger sample sizes might provide the statistical power to confirm these findings, they point out.
There was another important difference between the two training groups. "A lot of women enjoyed CrossFit more because they did different exercises each day," Wessel explained. However, the researchers did not specifically measure exercise enjoyment.
The two training groups appeared to differ in another important way, said Wessel. "A lot of women enjoyed CrossFit more because they did different exercises each day," she said, although the researchers did not specifically measure exercise enjoyment.
"These are good results, and similar to what we see in some of the other literature," said Yuri Feito, PhD, from Kennesaw State University in Georgia, who has coached CrossFit.
But the results would be more meaningful if the researchers had standardized the time and energy expenditure of exercise in the two groups, Dr Feito told Medscape Medical News.
He also questioned whether increased muscle could account for differences in strength between the groups, because the researchers did not show that the increased lean mass was localized to body parts responsible for particular exercises.
"I think the study has a lot of merit, we just have to compare apples with apples," he said.
This study was supported by a Western Kentucky University College of Health and Human Services faculty research grant. Ms Wessel and Dr Feito have disclosed no relevant financial relationships.