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Having trouble sticking to your exercise regimen? Maybe you're not doing the right exercises for your "fitness personality," suggests Linda Shelton, a fitness expert who spoke at this year's American College of Sports Medicine's Health and Fitness Summit held last weekend in Atlanta.

"Everyone has a fitness personality; their own exercise needs," Shelton told Reuters Health. Most people fail to stick with an exercise regimen, she said, because they are not exercising according to their fitness personality.

In her work, Shelton has identified five distinct fitness personality types, which she labels squares, rectangles, triangles, circles and squigglies — each has its own pitfalls.

Of the five personality types, "squares" are the most reliable, stable and predictable exercisers. They thrive on routine. "Squares tend to develop rigid schedules for themselves, so while they get to the gym, they don't see progressive results because they hit plateaus," Shelton explained in a statement from the meeting. "Instead, a square should try to take baby steps toward sprinkling in new activities weekly that switch up their routines while still giving them the familiarity of the old program."

"Rectangles" are a bit more flexible than squares, but still like order and routine. They love group exercise, Shelton said, and perform best with social interaction. Rectangles should join fitness clubs, like hiking or running groups, or take group fitness classes instead of exercising alone, Shelton advises.

"Triangles" are the most competitive and driven of the five fitness personality types. They are task-oriented and thrive on repetition when working out so they can monitor their progress and revel in their successes. "Triangles" need to have exercise goals and Shelton suggests they work out with an equally competitive partner or train with a specific event or goal in mind, like a mini-triathlon or half-marathon.

"Circles" are the social butterflies of the fitness world, according to Shelton, and the most emotionally driven of the five types. "Circles are the most common type in the fitness world; circles are spontaneous, social, would not exercise alone, they respond to group exercise, and they like to be with a trainer," she told Reuters Health.

A potential pitfall with circles is that they may spend more time socializing than working out. "Circles sometimes talk the entire way through a workout; they're not really there for exercise so much as camaraderie," Shelton said. "They need a nurturing trainer who will motivate them, yet not push too hard, or to exercise in a group setting."

And last but not least are the "squigglies" — the most outgoing, least structured fitness personality type of them all. They are the complete opposite of squares and hate routine. Squigglies must derive pleasure from whatever activity they're doing, or they may quit. Squigglies, Shelton said, need to have an extremely varied exercise plan that includes lots of different classes and new activities to maintain interest in exercise.

"Knowing your fitness personality," Shelton told Reuters Health, "and what your needs are and what you personally respond to is going to help someone like exercise, engage in it, reduce attrition and increase compliance because they are doing something that suits how they think and how they are."