COURTESY OF SPORTS ART

Recumbent bikes offer back support and a surprisingly good workout. This one, made by a Woodinville company, is the Sports Art 2002B, which features a two-piece seat with adjustable back, magnetic resistance, six programs displayed neatly on the flywheel casing, and infrared remote adjustment on a seat-side handlebar. ($899; Fitness Showcase.)

I USED TO WONDER why there were so few reviews and ratings of stationary bicycles. After a few weeks of checking them out myself, I think I understand why.

Exercise bikes can have as many variables to consider as another common piece of home equipment, treadmills. But individual fit on a bike can be trickier, since more parts of the body actually come in contact with the machine - sometimes when they're not supposed to.

On one bike I tried, the inside of my right heel kept grazing the belt-drive flashing at the bottom of each pedal revolution. On another, my right knee brushed the display console in front. If we needed to replace our more than 20-year-old Tunturi stationary bike (which we don't), I would have ruled out the one that drove my thighs into my belly, the one that slapped them against the seat and the several that cut into my own seat. Yet I don't doubt that those very bikes might suit other folks just fine.

So I'm as hesitant to recommend any one stationary bike as I am to recommend any one athletic shoe. That said, there are plenty of variables to keep in mind when shopping around:

Style

Conventional exercise bikes are upright, mimicking more or less the body position of an outdoor bicycle. Equally familiar to many users, however, is bicycle-seat numbness, or worse. Newer racing-type models, offshoots of Spinning and other intense group-exercise classes, have a direct drive - no coasting - and accommodate several hand and body positions. I've found, though, that even on our old Tunturi I can crank up the resistance and stand up to pedal, to vary a workout. Upright pedaling works primarily the muscles in the front of the thigh (quadriceps).

Recumbent bikes tend to be more comfortable because their seats have back supports, helping with low-back and numb-bottom issues. That comfort can be deceptive: Because pedals are positioned so legs are parallel to the ground (a true recumbent) or nearly so (semi-recumbent), you work against gravity more than on an upright, making for a harder workout, at least potentially. Driving the legs out, rather than down, emphasizes the back of the thigh (hamstrings) and gluteus maximus muscles.

Drive and resistance

Belt drives have replaced noisy, messy chain drives in virtually all stationary bikes, but the sound generated still varies widely because of different approaches to resistance.

Fan systems require you to pedal faster to make the workout harder. They're noisy but at least blow cool air on your as you ride. Some models are "dual-action," with poles to grab for a simultaneous upper-body workout. I find the arm movement awkward, though, and the benefits limited because resistance is linked to pedaling speed.

Flywheels let you increase pedaling resistance without increasing speed. In some, friction is caused by brake pads, which tighten on the wheel, usually by the turn of a knob. Although such pads can wear out, even upscale racing models tend to use them because they better simulate road riding. Most new bikes, however, use magnetic resistance: You turn a knob or use electronic controls to move one or more magnets closer to the flywheel to increase the drag. Some of these bikes are remarkably quiet.

Statistics display

Our old Tunturi has a timer that ticks and a glass-enclosed manual dial to indicate speed and log distance. Today even low-end modern stationary bikes have simple electronic displays for tracking speed, distance and calories burned. More elaborate displays can include resistance adjustments, preset programs, heart-rate monitoring (by ear clip, hand grip or chest strap) and workouts that combine all three and make customized changes automatically - a nifty feature. Some need to be plugged into electrical outlets, but others are self-generating - pedaling provides the power for the display. If you plan to watch TV while pedaling, take note of sight lines, since some consoles are quite tall.

Other factors

Is the seat comfortable? Are adjustments easy to make? Are seat posts and pedal cranks standard size, so you could customize, if desired? How much room does it require? Is the bike designed for home, light-commercial or commercial use? What is the warranty?

Prices of the more than 30 bikes I tried recently ranged from $99 to $2,695. Recumbents generally cost $100 to $500 more than their upright counterparts. If I wanted to upgrade, on a generous budget I'd go for one toward the higher end, since all those programming options are convenient and can be motivating. More realistically, I'd take longer test rides on the low-end magnetic resistance models, in the $600 to $900 range.

When trying out a bike, make seat and any other adjustments yourself. Change the resistance a few times, try all the features and stay on long enough - 10 minutes at least - to get a good feel in terms of controls and comfort. If more than one person will be using it, each should be included in the tryouts. Shop at reputable sports-equipment store that can help with questions, maintenance and service. I'd pay extra if needed to have it assembled by someone familiar with the process, but maybe that's just me.

And I definitely wouldn't buy an exercise bike from a shop like a few I visited, where a bike with an electrical cord wasn't plugged in so I couldn't try all the features, or the resistance dial wasn't working, or the whole thing tilted me to the right.

If the display model, the one that's supposed to help make a sale, isn't functioning properly, how do you suppose the one you take home will work?

Molly Martin is assistant editor of Pacific Northwest magazine.