Pfitzinger Pete: Advanced Marathoning

Your running economy determines how fast you can run using a given amount of oxygen. If you can run faster than another athlete while using the same amount of oxygen, then you’re more economical. This concept is similar to the efficiency of an automobile engine – if a car can travel farther using a given amount of gasoline, then it’s more economical than another car.

Running economy can also be viewed as how much oxygen is required to run at a given speed. If you use less oxygen while running at the same speed as another runner, then you’re more economical. If you know how much oxygen a runner can use at lactate-threshold pace, as well as that athlete’s running economy, you can generally predict marathon performance fairly accurately. In fact, a classic study by Farrell and colleagues found that differences in pace at lactate threshold predicted 94 percent of the variation in racing speed among distance runners (Farrell et al. 1979).

Running economy varies widely among runners. While testing elite runners in the laboratory, Pete has found differences of more than 20 percent in running economy among athletes. Obviously, a large advantage exists in being able to use oxygen as economically as possible during the marathon – your aerobic system supplies nearly all of the energy for the marathon, and oxygen is the main limiting factor in the rate of energy production by the aerobic system.

For example, say two athletes with identical lactate-threshold values of 54 ml/kg/min are racing at a pace of 5:55 per mile (per 1.6 km). Although it seems that they should be working equally hard, this often isn’t the case. If Stacey has an oxygen requirement of 51 ml/kg/min at that pace and Christine requires 57 ml/kg/min, then Stacey will be comfortably below lactate threshold and should be able to maintain a 5:55 pace. Christine will steadily accumulate lactic acid and will need to slow down. Stacey has a faster pace at lactate threshold because she uses oxygen more economically to produce energy.

The primary determinants of running economy appear to be the ratio of slow-twitch to fast-twitch fibers in your muscles, the combined effect of your biomechanics, and your training history. The proportion of slow-twitch muscle fibers is important because they use oxygen more efficiently. One reason that successful marathoners tend to be more economical than slower marathoners is because they generally have more slow-twitch muscle fibers. Runners with more years of training and more miles “under the belt” also tend to have better running economy, possibly due to adaptations that gradually allow fast-twitch muscle fibers to have more of the characteristics of slow-twitch fibers.

Running economy is also related to the interaction of many biomechanical variables, but no single aspect of biomechanics has been shown to have a large impact on economy. We don’t know, therefore, how to change biomechanics to improve economy. One of the problems is that it’s impossible to change one biomechanical variable without affecting others.

High Maximal Oxygen Uptake ( O2max)

Successful marathoners have high O 2max values. This means they’re able to transport large amounts of oxygen to their muscles, and their muscles are able to extract and use a large amount of oxygen to produce energy aerobically.

The average sedentary 35-year-old man has a O 2max of about 45 ml/ kg/min, while the average 35-year-old male runner has a O 2max of about 55 ml/kg/min. A locally competitive 35-year-old male marathoner tends to have a O 2max in the range of 60 to 65 ml/kg/min, whereas an elite male marathoner would tend to be in the range of 70 to 75 ml/kg/min. Although successful marathoners tend to have high O 2max values, they typically aren’t as high as the O 2max values found in elite 5,000-meter runners, whose maxes can reach as high as 85 ml/kg/min. Women’s O 2max values tend to be about 10 percent lower than those for men because women have higher essential body fat stores and lower hemoglobin levels than do men.

The primary factors in increasing O 2max appear to be related to improvements in the ability to transport oxygen to your muscles. This ability is related to four factors: your maximal heart rate, the maximal amount of blood your heart can pump with each beat, the hemoglobin content of your blood, and the proportion of your blood that is transported to your working muscles.

Your maximal heart rate is determined genetically. In other words, it doesn’t increase with training. Successful marathoners don’t have particularly high maximal heart rates, so it isn’t a factor in determining success.

The maximal amount of blood your heart can pump with each beat is called your stroke volume. If the left ventricle of your heart is large, then it can hold a large amount of blood. Blood volume increases with training, resulting in more blood being available to fill the left ventricle. If your left ventricle is strong, then it can contract fully so that not much blood is left at the end of each contraction. Filling the left ventricle with a large amount of blood and pumping a large proportion of that blood with each contraction result in a large stroke volume. Stroke volume increases with the correct types of training. In fact, increased stroke volume is the main training adaptation that increases O 2max.

The hemoglobin content of your blood is important because the higher your hemoglobin content, the more oxygen can be carried per unit of blood and the more energy can be produced aerobically. Some successful marathoners train at high altitude to increase the oxygen-carrying capacity of their blood. Other than by training at altitude (or through several illegal methods, such as taking synthetic erythropoietin, known as EPO), the hemoglobin concentration of your blood won’t increase significantly with training.

We’ve talked about the amount of oxygen per unit of blood and the amount of blood that your heart can pump. The other factor that determines the amount of blood reaching your muscles is the proportion of blood transported to your working muscles. At rest, just more than 1 liter of blood goes to your muscles per minute. During the marathon, approximately 16 liters of blood are transported to your muscles per minute. When you’re running all out, it’s more than 20 liters per minute. Much of this increase is due to increased heart rate and stroke volume, but redistribution of blood to your muscles also contributes. At rest, approximately 20 percent of your blood is sent to your working muscles; during the marathon, it rises to roughly 70 percent. With training, your body becomes better at shutting down temporarily unnecessary functions, such as digestion, so that more blood can be sent to your working muscles.

Successful marathoners are able to recover quickly from training. This allows them to handle a larger training volume and a higher frequency of hard training sessions than those who recover more slowly. The ability to recover quickly is related to genetics, the structure of your training plan, your age, lifestyle factors such as diet and sleep, and your training history. (The 30th 20-miler of your life will probably take less out of you than your first one.)