Whether the goal is to finish a marathon, polish a tennis game or make the most of that hour at the gym, fitness experts say pacing can spell the difference between success and stagnation.

Setting the proper workout pace, or the distribution of energy during exercise, deflects boredom and fatigue, syncs body and mind, and enables the everyday exerciser to keep pushing the envelope.

Dr. Kevin G. Thompson, author of "Pacing: Individual Strategies for Optimal Performance," believes how people prepare their bodies and minds for activity is limited by their lack of understanding about how to pace the exercise.

"Unless the athlete knows what the ideal pace is, how can he or she train properly to improve performance?" said Thompson, director of the Research Institute for Sport and Exercise at the University of Canberra, Australia.

His book details pacing strategies specific to activities from triathlons to tennis.

In marathon races, Thompson said, the classic beginner's error - starting too fast to try to keep up with the better runners - causes a mind-body split.

"You body's feedback says you're exercising too hard even as your brain knows you've still got a long distance to go," he said. "That makes for a negative experience."

Group classes, which usually cater to all fitness levels, are generally paced around a bell curve model, explained Donna Cyrus, senior vice president of programing at Crunch, a chain of U.S. fitness centers.

"In a 45-to 60-minute class, people start at a moderate level, push into harder exercises to a point of highest expenditure about 30 to 40 minutes in, then drop back down till the heart rate returns to its resting state," Cyrus explained.

Interval training, which involves alternating high intensity exercise with recovery periods, is another way classes are paced, according to Cyrus.

Neal Pire, a strength and conditioning specialist with the American College of Sports Medicine, said the talk test, also called the ventilatory threshold (VT) is a good way for the individual exerciser to gauge intensity.

It is measured by different levels. Below level VT1 speech is comfortable, but at VT1 it requires some effort. Above VT1 but below the next level, VT2, speaking is possible, but not really comfortable. At VT2, speaking is limited to a few words.

"Once you get close to Ventilator Threshold No. 2, where you can barely keep a conversation going, you are in that training zone where you're getting the biggest bang for your buck." Pire said.

"You want to stay just below that point to keep improving over time," he added.

Research shows that mental toughness is one pace-maintaining factor that separates the elite athlete from the casual exerciser, Thompson said.

"Towards the end of a long race, the non-elites will distract themselves from discomfort, say with music or thoughts of their family," he said.

"But an elite athlete will zone in on discomfort and use those feelings as a gauge to examine how much they have left."

(Editing by Patricia Reaney and Gunna Dickson)