Running is a simple sport, but it's not so simple that runners don't make lots of mistakes in their training. Ironically, many of these mistakes occur when runners are talked into making the training process too complicated.
Problems emerge when coaches and scientists substitute the true goal of training—better performance—with specific physiological objectives such as maximizing the muscles' ability to burn fat. These physiological proxies for performance are too often treated as the be-all and end-all of running fitness. They can be used to create training programs (and sometimes diet plans) designed to maximize this one dimension of the physiological recipe for running fitness without a care for how other dimensions are affected.
Invariably, these unbalanced practices stymie the progress of runners who are unfortunate enough to fall for the underlying doctrine.
The reality is that running fitness has numerous components, none of which is the be-all and end-all. It's best therefore to forget about physiology and focus on performance. The most effective way to maximize running performance is to follow a balanced training program that covers all of the physiological bases.
Let's take a look at three of the most commonly promoted performance proxies and see why placing too much emphasis on any of them leads to unbalanced, ineffective training.
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VO2 Max
The concept of VO2 max, an acronym for "maximum rate of oxygen consumption," was discovered by English exercise physiologist A. V. Hill almost a century ago. Hill observed that regular exercise training increased the maximum rate at which individuals were able to consume oxygen during workouts. He also noted that those individuals who were able to consume oxygen at the highest rates tended to perform best in fitness tests.
These observations led Hill and other exercise scientists of the time to conclude that VO2 max, also known as aerobic capacity, was the be-all and end-all of endurance performance.
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Subsequent research revealed that high-intensity interval training was the most efficient way to boost VO2 max—efficient meaning that small amounts of training at high intensity increase aerobic capacity more than small amounts of slower training. This finding led to the development of training programs dominated by speed work.
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There's no question that aerobic capacity is extremely important for runners. However, it is not really the be-all and end-all of running performance. Proof comes from the fact that runners commonly see their VO2 max plateau after two or three years of progressive training, yet their race times continue to improve for many years afterward.
For example, the great Paula Radcliffe hit a lifetime peak VO2 max of 73 ml/kg/L when she was 17 years old. At that age she ran 3000 meters in 9:23, which works out to a pace of 5:02 per mile. Ten years later, Radcliffe's VO2 max was unchanged. That year she ran a half marathon in 1:05:40, which works out to a pace of 5:00 per mile, or two seconds per mile faster than the pace she sustained a decade earlier (at the same VO2 max) for a race distance that was 10 miles shorter.
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The main reason Radcliffe's performance improved so much despite no change in her aerobic capacity after age 17 was that she became much more economical. Improvements in running economy are associated with how much a person runs, not how fast. So, while maximizing aerobic capacity requires that a runner do some fast running, maximizing running economy requires that a runner run a lot, and the only way to run a lot without overtraining is to run slow down most of the time.
What's more, a "mostly slow" training approach is also the most effective way to elevate VO2 max. A 2014 study by researchers at Salzburg University found that runners and other endurance athletes who did 57 percent of their training at high intensity for nine weeks saw a 4.3 percent increase in VO2 max, while athletes who did only 24 percent of their training at high intensity saw 11.7 percent increase in VO2 max over the same time period.
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Lactate Threshold
The lactate threshold, discovered in the 1970s, was quickly embraced by many coaches and runners as the new be-all and end-all of running fitness. For each runner, there is a certain speed at which lactate, an intermediate product of aerobic metabolism in the muscles, begins to accumulate quickly in the blood stream. This lactate threshold speed is strongly predictive of race performance. As an individual runner's threshold speed increases through training, his or her race times come down.
In all runners, the lactate threshold occurs at a moderate intensity that falls somewhere between that person's half marathon and 10K race pace. Running at this intensity is an effective way to increase the lactate threshold. For this reason, coaches who look at maximizing the lactate threshold as the overarching goal of training tend to create programs that include lots of moderate-intensity work in the form of "tempo" or "threshold" runs.
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This is a mistake. The problem with moderate intensity is that it is almost as stressful to the central nervous system as high intensity but is not as stimulative of fitness gains. There is a place for moderate-intensity running in the training process, but that place is a small one. This was shown by the Salzburg University study mentioned above. Athletes who did about half of their training at low intensity and half at moderate intensity saw their performance in a fitness test increase by 6.2 percent over nine weeks. This was a smaller improvement than what was achieved by three other groups of athletes who did less training at moderate intensity and more training at low intensity, high intensity or both. The biggest gains were experienced by athletes who did 68 percent of their training at low intensity, only 6 percent at moderate intensity, and 24 percent at high intensity. These athletes improved by an average of 17.4 percent in the performance test.
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Fat-Burning Capacity
Another physiological response to training that is associated with better performance is increased capacity of the muscles to burn fat for energy. This adaptation is important because fat is a far more abundant energy source than is glycogen, a form of carbohydrate that is stored in the muscles and liver. The better the muscles get at burning fat, the longer they can conserve glycogen stores, and the farther the runner can go in races before hitting the wall.
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Low-intensity running does the best job of boosting fat-burning capacity. But diet also plays a role. Runners who maintain high-fat diets are able to increase their fat-burning capacity beyond the level they can get to through training alone. Such diets have become quite popular lately among runners who have been persuaded that fat-burning ability is the be-all and end-all of running fitness.
The problem is that it's not. For better or worse, it is impossible to truly maximize the muscles' ability to burn fat without also impairing their ability to burn glycogen and glucose. And when this happens, a runner's aerobic capacity, anaerobic capacity and race performance decline. This was shown most recently by a team of Polish researchers, who found that four weeks on a high-fat diet (70 percent of total calories) reduced both lactate threshold power and time-trial performance in trained cyclists compared to a normal diet (50 percent carbohydrate).
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There Is No Substitute
While running is simple, its underlying physiology is complex. There is no single physiological factor that determines running performance independently of all the others. Everything matters—VO2 max, lactate threshold, fat-burning capacity and many others. The simplest and most effective way to enhance running performance is to forget the physiology and stay focused on performance itself.
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