The ultimate exercise machine, they say, is a dog. Almost any dog, although the last reader letter, if memory serves, specified a Jack Russell terrier, a la Eddie on "Frasier."

Last year the ever-practical Men's Health magazine (www.menshealth.com) came up with a rundown on which breeds were best suited for particular recreational activities (see box). Most match-ups might well hold true, though one friend questioned whether her or any other Irish setter would spend more time running alongside or biting the mountain bike's tires.

Dogs make good exercise partners because even people with a limitless supply of excuses for not exercising themselves usually can't put off the obvious:

The dog needs a walk.

Some need a run, some need to fetch, some to dig, a few crave a swim, but walking covers many of them, most of the time. And - wouldn't you know it - the same holds true for humans.

A dog well-walked is a dog well-adjusted, less likely to drive its family crazy from hyperactivity or chewed-up slippers. A human well-walked (say, 30 minutes briskly each day) reduces its risk of death by 50 percent, though it still might find other ways to drive the family crazy.

Some lucky pet dogs get to do what their breeding tells them to do: I have a friend who feigns drowning off their dock on Lake Washington so their Newfoundland has a chance to rescue her and swim while pulling a load.

At Green Lake one recent Sunday I talked with Maia Halvorsen of Bellingham, who was visiting her brother and jogging with his dog, a shepherd-Lab mix that liked jogging better than walking. Back home, Halvorsen had another jogger, a German shepherd, but also an Alaskan malamute-Chesapeake Bay mix. "She just likes a dead run," preferably in the lead, ideally pulling something.

So Halvorsen has rigged a harness the dog can wear while pulling her on inline skates or, in the winter, on skis. "She just loves to pull," Halvorsen says. "The hard thing is teaching her how to heel."

Look in a book on dogs, and it's obvious that exercise is part of their life's blood. Breeds are grouped under "sporting," "hounds" and "working." Even terriers are bred for specific active purposes. Prospective dog owners might browse a bookstore or two for "exercise requirements" before committing. "The Roger Caras Dog Book," for example, rates most sporting dogs as 6s to 10s on a scale of 1 (needs little exercise) to 10 (many long walks and free runs), and hounds get mostly 9s and 10s. Terriers can vary from the Australian (4) to the Airedale (10), as can toys: Chihuahuas get a 1, toy poodles a 6.

Individual temperaments also figure in, as with a Pomeranian I saw at Green Lake. According to Caras' book, Jasmine was a 2, for whom "even a brief walk with her short legs seems likes miles." But Jeanne McCarthy and John Schreuder walk her three times a day, about an hour total, and say she keeps up with about a seven-minute-mile pace. On a recent eight-mile hike, she did fine - "Just if the rocks are too big, we've got to help her over," says Schreuder.

"The only thing you can't do with her is sit-ups," McCarthy says, "because she'll get in the way - she wants to play."

A lucky few come upon a dog that can exercise itself. My friend with the Newfie also has a golden retriever, which is not renowned (among humans) for its intelligence. But this dog, Natches, although happy enough if someone throws a ball or a stick for him to retrieve, doesn't need the human intervention.

He'll find a tennis ball, roll it off the dock, jump in after it, swim ashore, and promptly roll the ball off the dock again.

Only in the summer.

Who's the smart one here?

Molly Martin is assistant editor of Pacific Northwest magazine. ------------------------------- Dogs at Play

The top dogs for a few popular recreational activities, according to Men's Health magazine:

Running: Australian cattle dog. Also-rans: Brittany and other spaniels, Siberian husky, Saluki and Belgian sheep dog. Avoid: Smaller dogs such as dachshund and Shih Tzu.

Fishing: Basset hound. Also-rans: Bloodhound, mastiff. Avoid: Dalmatian, poodles, Chihuahua.

Frisbee/fetching: Retrievers. Also-rans: Cocker spaniel, Shetland sheep dog, Australian shepherd, Rottweiler. Avoid: German shepherd, Saint Bernard, other large dogs.

Camping and hiking: Pointer. Also-rans: Boxer, retrievers, Rhodesian Ridgeback, vizsla, Weimaraner. Avoid: Shih Tzu, other non-runners.

Mountain biking: Irish setter. Also-rans: Golden retriever, whippet, greyhound. Avoid: Small, low-to-the-ground dogs.

Cross-training (loafing one day, canyoneering the next): Flat-coated retriever. Also-rans: Labrador, Belgian sheep dog. Avoid: English bulldog. ------------------------------- NOTEBOOK

Muffin mistake

Reading my column last month, Erika Ellis caught me making a common mistake. I'd passed along the calorie count of Biringer's low-fat and fat-free muffins, but assumed one muffin was one serving. Wrong! Ellis asked the right question and learned that one serving is half a muffin, which means that instead of being 170 calories for the low-fat and 210 for the fat-free, the muffins have 340 and 420 calories. "That is still about half of the calories of regular fatty muffins the same size," she writes, "but by no means are these `healthy' muffins low-calorie."

Life without Spandex

I've wondered who buys all that tight-fitting workout clothing we see displayed in stores everywhere. Looks as though I'm not alone. Loose or baggy workout clothes were preferred by 78 percent of women in a recent national survey for the Sports Apparel Products Council. Even in the 21-to-31 age group, only 30 percent preferred fitted tops and bottoms. Women surveyed asked for more apparel designed specifically for women. Among men and women, 80 percent said they wore sports apparel at home while relaxing, 76 percent for physical activities, 70 percent for working around the house, 53 percent on weekend outings, 40 percent traveling, 30 percent shopping and 28 percent to work on casual days. Very casual, presumably.