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LIMITATIONS ON PHYSIOLOGICAL PREDICTORS

Recently, a promising young distance runner named Ben did a fitness test at a local gym to determine his VO2 max. The gym didnít explain that his VO2 max was not actually being measured, but just predicted from a formula. Benís predicted VO2 max was 57 ml/kg/min. He was crushed, as he knew that other top young runners typically have VO2 max values in the high 60s or even the 70s. Ben left the gym dejectedly, thinking he was destined for mediocrity. A few weeks later, Ben reluctantly underwent a VO2 max test in our lab. Much to his surprise, he reached 74 ml/kg/min, which indicates outstanding potential.

Marathoner and former RT Editor Gordon Bakoulis was tested at the U. S. Olympic Training Center in Colorado Springs in 1990. Based on her VO2 max test, lactate threshold test and marathon race times, Gordon was advised to do her 800 meter repetitions on the track in 2:28. This was useful advice from some of the best exercise physiologists in the country, with the only hitch being that her personal best for 800 meters was 2:26.

Why did these predictions not work particularly well for these runners? There are several possible reasons, including genetics, training history, mental approach, and misinterpretation of statistics. Letís take a look at each of these factors.

Genetic make-up
Why were the 800 meter times recommended for Gordon too fast for her? Well, Gordon is what you could call a ďmarathonerís marathoner.Ē Although the percent of slow twitch muscle fibers in Gordonís muscles was not measured, it is a fairly safe assumption that she lives far out in the slow twitch galaxy. Using data from the lab and race times to determine the most effective pace for 800 meter intervals works very well for a typical national class womenís distance runner. But Gordon isnít typical-her high proportion of slow twitch muscle fibers helps make her ideally suited for the marathon, and not so well-suited to shorter distances. So, try as she might, Gordon cannot do repeat 800s in 2:28, and the quality of her 5K time will never be equivalent to her marathon time.

Training history
Of course, we donít really know much about Gordonís genetic makeup at all. Perhaps she has just trained as a marathoner for so many years that now, in a sort of self-fulfilling prophecy, she is ideally suited for that event. This often happens when a runner gains positive reinforcement from doing one type of training more than another. We all tend to do what we are good at, and avoid the types of training that are, well, embarrassing. For a distance runner it can go 2 ways-you may be naturally good at intervals on the track and struggle on long runs, in which case you will likely hit the track frequently. Or, you may loath interval work but really enjoy thrashing your training partners on your long runs. Due to avoiding speed training, runners in the latter category tend to run 10 K races at a pace that is only slightly faster than their marathon pace. To reach your full potential as a runner, you need to train your strengths but also neutralize your weaknesses.

Novice runners will often not fit the standard race equivalent charts for the longer distances. A long-time runner who cranks out a 10 K in 44 minutes would be predicted to do a marathon in about 3 hours and 30 minutes. If he has only been training for 2 years, however, then he would likely not have the training base to maintain such a strong pace for 26.2 miles.

Mental factors
Mental factors also come into play in whether or not you ďfit the formula.Ē If you have a bad experience in your first marathon, that experience may stay inside your head for years and prevent you from reaching your true marathon potential. If you believe that you cannot run a reasonable time in the marathon, then you are very, very unlikely to ever run a reasonable marathon. The key to overcoming a defeatist attitude about a given type of race is to provide yourself with opportunities for positive reinforcement during training that break down your negative perception.

Misinterpretation of statistics
Benís low predicted VO2 max test occurred because while formulas tend to be fairly accurate for someone who is moderately fit, they can be highly inaccurate for someone like Ben who is highly fit. In addition, formulas often work well for large groups of people but are highly inaccurate for any given individual. For example, the basic formula for predicting maximal heart rate of 220 beats per minute minus age predicts a max heart rate of 175 bpm for a 45 year old. Indeed, the average maximal heart rate for 45 year olds is very close to 175 bpm. The problem is that some 45 year olds have maximal heart rates much higher than 175 bpm and others much lower. In fact, all the formula tells us about any individual 45 year old is that there is a 95 percent likelihood that she has a maximal heart rate between about 155 and 195 bpm. Using this formula, therefore, provides useful information on the average maximal heart rate for a large group of people your age, but potentially misleading information for you. Unfortunately, these formulas tend to be utilized strictly by gyms and fitness equipment manufacturers, who often provide unreliable information to athletes.

So, if you use a formula to predict some aspect of your physiology or performance, remember that it is only a prediction. Most runners know a great deal about their bodies, so if a prediction seems absurd to you, then it probably is.

(This column originally appeared in Running Times Magazine.)