Mental Gymnastics : Exercise: In the midst of a workout or run, you find your mind’s a million miles away. It’s called disassociation and athletes say it’s like a vacation.

“A nother glass of Orvieto, sweetheart?” you ask as you prop yourself on the velvet cushions and reach for the ice bucket. The gondolier is averting his eyes, but Candice Bergen, looking un-Murphy Brownish, isn’t. She smiles as you float beneath the Bridge of Sighs, and soft mandolin music drifts by on the Venetian summer air . . .

So why are your legs starting to feel like Jell-O? And where did that burning feeling in your throat come from? Why is that stinging sweat rolling in your eyes? Why are you wearing Nikes? And what happened to Candice?

Welcome back to Mile 4 of your daily run, after you’ve been doing it again--letting yourself sink into the random mental state that seems to occur when people perform a repetitive athletic activity.

You could be riding a stationary bike, swimming laps, or reeling off miles at the local track. But your mind is balancing your checkbook, planning your next day’s schedule or replaying your prom date.

Athletes call this state disassociation.

It’s the ability--or tendency--to take the mind off the business at hand and let the body work while the brain takes a vacation.

“If a runner is going to run 10 miles on a training run over a familiar course, for example, he’s not going to worry too much about what’s going on,” said Dr. Brent Rushall, a professor of physical education at San Diego State University who has studied the effects of concentration--or the lack of it--on athletic performance.

“The stimuli will be familiar to him. He can then think about things that happened at work, run through problems, plan a paper he’s writing, plan a vacation--things totally unrelated to his performance,” he said. “Some younger people tend to disassociate for a while and fantasize that they’re in the last mile of an Olympic final. It can be a whole mishmash of thinking to get over the repetitive boredom.”

Olympic champion swimmer Janet Evans never knows what thought will materialize during long training swims. “When we’re doing a really long set in training,” she said, “sometimes you set a pace and let your mind drift, like to how much homework I have to do when I get home, what happened during the day. It gets boring to think about swimming during a workout. Sometimes I’ll think of things that happened a long time ago. They’ll just suddenly be there. When I train with my teammates, all of a sudden--I don’t know why--I’ll think about a meet or something that we were at that happened a year ago--just a random thought.”

The mental meanderings may be largely unexplainable, Evans said, but “I like it. It gives me a chance to be myself and work a lot of things out in my mind.”

A running regimen has a similar effect on Sen. Alan Cranston (D-Calif.). Long a devotee of running, Cranston said he is primarily a sprinter, but sometimes uses one- and two-mile runs to warm up.

“I just try to use that as relaxation and as an escape from work and responsibilities,” he said. “Now and then, if there’s some problem I haven’t figured out, I may get an inspiration about how to deal with it. The human mind works that way, when you let it work subconsciously.”

Disassociative thinking in repetitive exercise may be almost instinctual, John Jerome wrote in his book “Staying With It: On Becoming an Athlete.”

“Primitive societies,” he wrote, “know there is considerable power in rhythmic, repetitive physical action--as in nonstop dancing--to affect the mood, if not to move the consciousness into mysterious regions.”

The late Jim Fixx, a prime mover in the ‘70s running boom, wrote in his “The Complete Book of Running” that “while writing two books on games, puzzles and human intelligence I often solved problems as I ran. It was hard work (I’m not much good at doing math without pencil and paper), but if I concentrated, I could usually accomplish something. The kind of thinking I most like to do while I run, though, is just to let my thoughts wander wherever they wish.”

This isn’t the same as the “runner’s high,” usually ascribed to a release of natural, pleasure-inducing endorphins in the brain after a certain level of exertion has been reached. Disassociation, runners and others report, is more like daydreaming.

There are times, however, when athletes must concentrate to avoid injury or to improve their performance.

“You disassociate through a lot of your training,” said Olympic champion marathoner Frank Shorter. But “in competitions, you don’t. There, disassociating is not an advantage. When people try to take their minds off an activity, they’re not the ones who are going to be best at doing it. The elite runners think about where they are, what their effort is, how they’re doling it out, what their competition is.”

Recreational running, however, “is completely thinking about things that don’t affect performance at all,” Rushall said. “The people running in the back of the pack in a marathon are building houses in their minds and thinking about how people are going to be so surprised that they’re in a marathon. But the elite runner is really working on the ingredients that fine-tune his running.”

In competitive team sports, where the mind must stay focused even in practice, that discipline often remains, even in repetitive training, two Los Angeles Rams said.

“It depends on how you feel about your body,” said safety Vince Newsome. “If you don’t care too much about it, you don’t have to work out as hard and you can let your mind wander. But for an athlete, even if you don’t have to concentrate on what you’re doing, somewhere in the back of your mind you’re always kind of concerned, because you don’t want to get terribly out of shape.”

During heavy training, said linebacker Brett Faryniarz, “you concentrate on what you’re doing. You have to concentrate when you’re working with weights if you want the results.”

Still, said Newsome, “your mind can go off different places and can either help you with your lifting or it can hurt you. When some people lift, they think about their opponent, but some think about a problem they’re having at home. Each individual has his own method or thought process.”

Sometimes, Evans said, a little artificial stimulus to the imagination can’t hurt: “You’ll see a lot of swimmers listening to Walkmans before they swim. They’ll be fast songs that are kind of uplifting. In the race, your mind will be focused the whole time, but there’ll be this song you’ll be singing in your head. Swimmers will talk to each other later and say, ‘Hey, guess what song I was singing during that race.’ It’s really weird.”

Sometimes it’s necessary to keep the mind engaged for no other reason than one’s personal safety.

Bill Leach of Irvine, who competed with his wife, Julie, in kayaking events at the Montreal Olympic Games in 1976 and now competes in triathlons, warned that “it’s very scary to let your mind wander when you’re on a bike, because you could end up having a crash. Sometimes you have to almost force yourself to pay attention.”

John Rosmus, of Fullerton, an ultra-long-distance runner who completed 65 miles of a 125-mile dash across Death Valley early this summer, said that in potentially dangerous situations, “you pretty much think about what’s going on inside your body and how you’re feeling from mile to mile. You think about where the next aid is coming up. You’re monitoring yourself.

“You have to keep your mind on the trail and watch for rocks and things,” said Rosmus, who intends to try his trans-desert transit again. “Otherwise you’ll be falling all over the place.”

Still, said Rosmus, when the path levels and grows monotonous, “you think about things that are just off the wall, just day-to-day things. Sometimes you can’t figure out what you’ve seen in the last 10 miles. You’ve covered the ground but you don’t know how you’ve gotten there.”

That sort of fatigue, Evans said, can cause the mind to wander as easily as the more relaxing atmosphere of an easy workout: “During a really hard set, where we’ve been going for a long time at about 95% or 100% effort, you have to get your mind off swimming and you can get these random thoughts. It’s almost like you’re delirious.”

In extremely long, sustained efforts, Rushall said it is essential for athletes to pull their minds away from the task, at least for a while. In advising competitors in the grueling Iditarod sled dog races in Alaska, Rushall suggests that they think about “how their sled is running, how the dogs are doing. But when they come to, say, an eight-mile flat stretch they should disassociate, take a mental vacation. They should think of how beautiful the scenery is and how it’s quite a nice place to be and break off from the sled racing itself.”

The ability to disassociate doesn’t come instantly, Shorter said. Those who are out of shape, when embarking on a repetitive training regimen, won’t be thinking about twittering birds and sylvan glades after a mile or so.

They will be thinking about fatigue.

“If you’re not in good shape to begin with, there’s an intellectualization that you have to go through,” Shorter said. “You have to rely on faith. It’s that faith that will take you through those first two months to the point where it’ll be more enjoyable. There’s a certain base level of conditioning that you have to get to before you can start to not think too much about what’s going on.”

When Julie Leach of Irvine reached that stage, she went straight past it, into the realm in which she concentrated on every aspect of her workout, not only for kayaking but for triathlons. She got so good at it that she won the women’s division of the Ironman Triathlon in Hawaii in 1982. Today she is a recreational runner and cyclist.

In recreational efforts, she said, “you don’t need to concentrate on the workout and be really serious about it. You can be imaginative. My advice would be not to concentrate on things like ‘This really hurts’ or ‘This is really hard.’ You can mentally control yourself so much by what you suggest to yourself.”

And with such thoughts, said her husband Bill, comes the real payoff--those times when the mind is freewheeling, at peace “and you’re really relaxed. The time goes by and you’re not conscious of it. You feel very comfortable. It’s those times you relish, because that’s what it’s all about. You’re looking for that feeling of effortless effort. It’s a feeling that’s almost euphoric. It’s almost a bigger-than-life feeling.”