DENVER -- One of the main reasons people give for not belonging to a gym or working out is simply a lack of time. Knowing how to burn the right calories and getting the most out of your gym time is key.

One of the biggest mistakes people make at the gym is over-exaggerating the number of calories they’re really burning.

Luis Alonso, a certified metabolic technician, said you can’t trust the amount of calories cardio machines say you’ve burned.

“They’re completely inaccurate. It’s just a doodad. It has nothing to do with your individual metabolism and how you burn calories," Alonso said.

He said everyone burns calories at a different rate -- depending on sex, size, fitness level, and individual metabolism.

To find your best calorie burning rate, Alonso recommends getting a metabolic test. The test measures a person’s aerobic base -- the optimum heart rate for efficiently burning fat. At this rate, a person will burn half of their calories from fat, which is the goal. If the person reaches a heartbeat above -- or below -- their optimum heart rate, they won’t burn as many calories from fat.

Another problem at the gym is that people often do the same exercises.

Fitness trainer Bob Esquerre said it’s critical to frequently change the intensity and resistance of your workouts.

“Your body gets so used to it, you’ll plateau, and all of a sudden, you’ll start regressing," Esquerre said.

One big tip is don’t lean on the machines. One study shows leaning can reduce calorie burn by 60 percent.

A metabolic test also measures anaerobic threshold -- the exercise point at which your body physically can’t burn any more fat.

Alonso said metabolic testing has recently become mobile and user-friendly and will revolutionize the fitness world as it makes its way into more centers.