There is virtually no evidence from controlled scientific studies that high-volume training is optimal for developing endurance fitness.
High-volume training is optimal for developing endurance fitness.
Both of the above statements are true. The reason there is virtually no evidence from controlled scientific studies that high-volume training is optimal for developing endurance fitness is that it’s almost impossible to design and execute a study that properly tests the effects of high-volume training on endurance fitness.
Here’s why: In order to properly study the effects of high-volume training on endurance fitness, you need to start with previous untrained subjects. Of course, untrained individuals cannot handle a large volume of endurance training. So it’s necessary to start them off at low volume and gradually increase the amount of training they do until they stop improving, comparing their degree of improvement along the way to controls who train differently (the obvious alternative being a low-volume, high-intensity approach).
Judging by real-world evidence, it would take years for previous untrained subjects undergoing such a protocol to reach a training volume that ceased to provide additional fitness benefits. Paula Radcliffe is a great example. It took her 14 years to build up from running 30 to 40 miles per week to running 140 to 150 miles per week, at which volume she achieved her finest performances. It goes without saying that most people could never handle 140 to 150 miles per week of running, but nevertheless we can be certain that it would take years for even the average person to build up to his or her individually optimal volume of training. It is simply not practical for scientists to rigidly control the exercise patterns of volunteers for such a long period of time, and thus it has never even been attempted, and thus there is virtually no evidence from controlled scientific studies that high-volume training is optimal for developing endurance fitness.
What scientists do instead of devoting years to properly testing the effects of high-volume training on endurance fitness is compare different intensities of exercise in short-term studies. But such studies are inherently biased toward high intensity because although previously untrained individuals are not capable of training at high volumes, they are fully capable of training at high intensities in small doses. These comparisons therefore invariably conclude that a minute of high-intensity exercise has a bigger impact on endurance fitness than does a minute of low-intensity exercise. As valid as this conclusion may be, it is completely irrelevant to the interests of endurance athletes seeking performance in the real world.
I suppose if you only have a few minutes a week to train for a marathon, you’re better off sprinting. But if you only have a few minutes a week to train for a marathon, you’re better off not training for a marathon. Otherwise, you need to look to real-world best practices, not to science, for guidance on how to build fitness.
To realize your full potential as an endurance athlete, do like the pros: Start by doing 80 percent of your training at low intensity and 20 percent at moderate to high intensity in an overall amount that is challenging but manageable for you. Over time, as your tolerance grows, gradually increase your training volume, being sure to maintain an 80/20 balance, to reduce your volume for recovery in every third or fourth week, and to take one or two good, solid breaks each year. Continue this process until you feel that increasing your training volume any further would provide no additional benefit.