A new threshold: forget about your target zone—here's a smarter way to train

a MY ROBERTS, PHD, WANTS MY blood--and she's getting it, along with my sweat, as I pedal furiously on a stationary bike. She's testing my lactate threshold, and every two and a half minutes, I extend my fingers for another prick of the needle. Meanwhile, her assistant loads more and more weight on the bicycle's flywheel.

Heart rate climbing and drool dribbling down my chin, I breathe through a tube connected to a machine that measures my power output and vital stats. I've been at this for 20 minutes, and in the window's reflection I can see that my face has gone full-on tomato red. Roberts urges me on until I can't do any more. I'm toast--and I'm delighted. Why?

Because finding out your lactate threshold--and, in turn, plotting your anaerobic threshold--is like getting a detailed map to the Holy Grail when it comes to planning and maximizing training.

"It's the gold standard," says Roberts, a sports scientist at San Francisco's Sport and Health Science center. "Unlike generalized heart-rate formulas, which a lot of people use as training guidelines, your lactate level is a completely individual physiological response to exercise."

THE TROUBLE WITH TARGET ZONES

You're probably familiar with those heart-rate formulas that Roberts is referring to, the ones found on charts at most gyms. You're supposed to glance at these charts and find your "target zone"--the range of heart rates optimal for improving your fitness. But there are two problems with this approach. For one thing, there isn't single target zone that works best for training; there are actually several zones you should spend various amounts of time training within (see "Zone Power" for details). Second, the formula commonly used to determine the target zone--220 minus your age--can be wildly inaccurate for any given person.

A much more scientific approach to training, the one that Roberts is using, involves testing your V[O.sub.2] max, a highly individualized measure of aerobic power, and your lactate threshold, the point at which you start "feeling the burn." The testing procedure also reveals your anaerobic threshold, the point at which your body switches from aerobic mode (fueled by oxygen) to anaerobic mode (fueled without oxygen) and your muscles start to fatigue.

Taken together, your lactate and anaerobic thresholds provide a clear picture of your current fitness level. Armed with this information, along with your power output, your tester can determine your specific heart-rate training zones. Knowing these zones and how to intersperse them in a workout program enables everyone from weekend road racers to highly competitive athletes to fine-tune their training programs and ultimately improve performance.

I'd had my lactate levels tested earlier in the year in Connecticut, going along with friends for a lark. But I took what I learned to heart and changed my training habits by including higher-intensity running sessions with my rowing workouts and putting to use the heart-rate monitor that had been gathering dust in my closet.

Now, five months later, I was feeling more fit, but I wanted some hard evidence to know whether my new approach had really made a difference. I also found myself more curious about what exactly all these numbers meant. So, I turned to Roberts, and here's what I learned.

LACTIC ACID: FRIEND NOT FOE

Contrary to popular belief, lactate, or lactic acid, is not a demon. True, its buildup will cause a burning sensation during or after a hard workout, but it is neither a toxin nor a waste product. It's a vital link in the metabolic chain that converts carbohydrates into energy, and it's essential for high-intensity exercise.

The process works like this: Long-term contraction of the muscles taxes the circulatory system, making oxygen delivery more difficult, which in turn disrupts the metabolic chain. The mitochondria, or the powerhouse of the cell, can't keep up with the metabolic breakdown of energy, and some of the carbohydrate byproduct spills over and is released into the blood as lactic acid. As your muscles begin to feel the burn, the body goes into buffer mode, and you release the excess lactate as carbon dioxide as you breathe. When this occurs, you've reached your lactate threshold.

The relationship between your lactate threshold and your maximum exertion, a.k.a. V[O.sub.2] max, indicates your current level of conditioning--and the higher you can push this curve, the better. For example, if your lactate threshold occurs at 85 percent of your V[O.sub.2] max (often measured by its corresponding heart rate), then you're pretty efficient with your fuel breakdown and can probably maintain that level of intensity for some time. On the other hand, if your lactate threshold occurs at 65 percent of your max and you usually push your training intensity higher than this, your fuel breakdown can't keep up, and you'll likely run out of fuel and "bonk."

THE TRAINING PRESCRIPTION