"The more you do, the better it is" is not a maxim Shane Provstgaard believes in when it comes to high-intensity strength training.

With focused effort in the gym, he says, people need at most three strength-training sessions a week, each lasting 20-30 minutes, with a repertoire of five to eight really good exercises, properly executed. As you get better at it and develop more strength, it actually takes "less and less and less. I have people training with high intensity on strength every seven to 10 days," says Provstgaard, a personal trainer and fitness instructor with bachelor's and master's degrees in exercise science.

Provstgaard and fellow Utahn Craig Nybo are the authors of "Total Human: The Complete Strength Training System" (Authorhouse, $24.95).

You need a structured program and a certain level of intensity. You also need to know how to properly execute the exercises, with the proper range of motions and how to lift if you want results instead of injuries, he says.

He tells people to find a good book or video that shows them how to perform the exercise, then pay attention to how fast they lift and lower the weights. They should begin, he says, with the largest muscle groups and work their way to the smallest.

The benefits, they agree, are huge. Besides liking the way strength training makes muscles look, it pulls on tendons, which pull on bones, which pull on ligaments, strengthening the entire body. And that's really important as people age, because time itself reduces bone and muscle mass.

Muscle mass is the body's engine, Provstgaard says, and as it gets stronger and leaner, it burns more calories, so people can eat more and stay leaner, avoiding health consequences associated with being overweight.

You can't be strong, though, unless you give your heart a good workout, too. Cardiovascular exercise takes more time than strength training and needs to be done more often. Both are central components of fitness, they say.

Provstgaard says people often make the mistake of overdoing. You need to stay out of the gym long enough to recover between strength-training sessions. "All you're doing in the gym is stimulating the muscle to grow. It doesn't actually grow until you're out of the gym, relaxing and recovering. Some people need up to 20 days between. So you need a journal to know what you're doing. Otherwise, you're walking to New York without a map. You might get there, but you probably won't."