Calling all fitness Luddites and low-tech aerobic warriors—it's time to change your ways. Let us unlock the mysteries of heart-rate training and help you maximize your workouts.

By Paul Scott

David Arky

AT WHAT POINT does a gizmo make you stupid? When you start making cell-phone calls from chairlifts? When you turn to your GPS instead of the local gas station for directions? A gizmo put a "stupid" sign on my back this past November. I was on a run, trying out Polar's brand-spanking-new S510 heart-rate monitor (HRM, in fitness parlance)—$260 worth of chest-belt transmitter and wristwatch—and its myriad functions prompted a frantic button-pushing, run-aborting meltdown. In my own defense, I had reason to get confused: This little beauty, all curvy lines and sexy displays, tells you not only your current heart rate, but your resting heart rate, your estimated maximum heart rate (MHR), and your percentage of MHR, as well as high, low, and average rates. You can program ideal heart rates for various portions of your slog, and the S510 will enforce these zones with pleasant little beeps when you push too hard or, in a fit of slackness, back off too much.

Wait, there's more! You also get cycling-specific functions (average speed, max speed, trip distance, total distance, and an optional cadence feature), as well as the requisite bike attachments to collect the data. There's the first-ever self-administered VO² max test (derived from heart rate). There are timers within timers, a bevy of calorie-crunching functions, and a proprietary "SonicLink" that chirps a month's worth of workouts into your personal computer for ever-more-anal record keeping. I'm not sure, but I think the S510 will also file your taxes.

For those who claim such high-tech gewgaws are a sign of civilization in decline, a retreat from the purity of sport, this would surely be Exhibit A. Yet with 5.5 million folks nationwide using HRMs, including everyone from trail runners to circuit trainers, these devices are no longer secret weapons for the fitness elite: They've gone mainstream. Count me among the believers, now that I've achieved oneness with my S510 (no more trailside conniptions). The reason is simple. Conventional gauges of athletic achievement—distance and time—are relatively anemic. So you ran three miles in 25 minutes. Were there hills? Did you start out wiped or fresh? Battle a headwind? You get the idea. What you need is a way to track the intensity of your workout, and your perceived exertion is only part of the equation. HRMs may have a learning curve, but this is the thing—they are nearly perfect measuring devices. "Use it right," says Ed Burke, author of Precision Heart Rate Training, "and your endurance will skyrocket."

The philosophy of heart-rate training, in general, is based on the four intensity zones of exercise workload—recovery, aerobic, threshold, and anaerobic. Recovery entails easy work that doesn't significantly increase your breathing or raise your pulse past 60 percent of your maximum heart rate. Aerobic output is exertion with enough oxygen to keep your muscles working efficiently at 70 percent of your MHR, strengthening the lungs and cardiovascular system. Threshold exercise—at "race pace," roughly 80 percent of your maximum heart rate—takes you to the edge of anaerobic metabolism, when you simply can't take in enough oxygen to meet your body's demand. Here your heart pumps at 85 percent or more of its maximum, and lactic acid, a byproduct of anaerobic metabolism, causes your muscles to burn, cramp, and fail. Train at threshold with enough diligence and control, however, and you can increase your ability to process oxygen at the cellular level—your VO² max. Congrats. You're now stronger at speeds that used to shut you down.

But your HRM is there to tell you what your head and your lungs can't. "If your heart-rate monitor shows you a number that's normally comfortable, but you're now hurting, that means you may have overtrained," says Jay Blahnik, a nationally known fitness expert based in Laguna Beach, California. "If a heart rate feels better than normal, conversely, it may be time to push yourself."

Aerobics instructors have been telling people to check their pulses using the finger-on-the-neck method for decades—mostly to keep clients from falling over in a sternum-clutching heap. But the inaccuracy of palpating your carotid artery is one of the dirty secrets of the fitness world—with upward of 2.5 beats to count each second, it can be off by as much as 25 beats per minute—and it's impractical for anyone riding a bike or running a trail. Early HRMs weren't much better—imagine running with a wire clipped to your earlobe or fingertip—and neither were the first wireless models, which had clunky wristwatch units and often picked up signals from other athletes' HRMs. But since their first appearance, in 1977, chest-strap transmitters have become some of the most trusted tools available to sports labs, performing at 99.9 percent of the EKG gold standard. They've gotten cheaper, too. Though you can still pay as much as $700 for a unit with all the bells and whistles, most of the half-dozen brands out there offer midrange models for the price of a pair of running shoes (see chart at left).

First-time buyers should keep it simple—extra functions can be a liability if you don't need them. Save the calorie-crunching for the grocery aisles and the downloaded spreadsheets for your rotisserie football. Look for an accuracy rating of at least 90 percent of the EKG standard, a coded-signal chest strap (so your watch doesn't pick up the arteriosclerotic sack of Spam pumping in the monitor-wearing huffer next to you), big, readable numbers, and programmable training zones.

Eventually, and maybe a little ironically, your aim is to grow so comfortable with your monitor that it is no longer necessary. "The ultimate goal is to be able to do workouts with and without a heart-rate monitor," says endurance coach Ray Browning. "It should be an educational tool. Something to help you say, 'Oh, this is what a 70-percent effort feels like,' without always being attached to a number. That's using technology to its maximum benefit."   

Paul Scott wrote about outdoor winter training in the December issue of Outside.