Unless you fell onto this blog through a trapdoor and you have no clue what you’re doing here, you know that I am a proponent of the 80/20 training method, which entails spending about 80 percent of your training time at low intensity and the rest at moderate and high intensities. This does not mean that I believe every athlete should always do exactly 80 percent of his or her training at low intensity. There are more general, non-quantitative ways of stating my core philosophy of endurance training that do a better job of getting at its essence. For example:
Intensity balance is the single most important variable in endurance training. The single most beneficial thing you can do in your training is to consistently maintain an intensity balance that is heavily weighted toward low intensity yet does not neglect high intensity. The single most common and costly mistake that endurance athletes make in training is to spend too much time at moderate intensity, way too little time at low intensity, and also too little time at high intensity.
These statements are strongly supported by both real-world evidence and scientific research, and the last of them in particular has gotten further scientific support from a cool new study published in The Journal of Strength and Conditioning Research. Conducted by a team of researchers at Belgium’s Ghent University led by Jan Boone, the study involved 11 recreational cyclists training for a mountain-climb event. Over a 12-week period, each subject trained as he or she saw fit while wearing a heart rate monitor to collect data that was then passed on to the researchers. Before and after this 12-week period, all of the subjects underwent testing to assess various aspects of their fitness level.
The main purpose of the study was to test the power of certain ways of measuring training load to predict changes in fitness. Training load is a function of both the volume and the intensity of training. Because there was a great deal of variation in the volume and intensity of the training that the 11 cyclists involved in this study did in preparation for the mountain-climb event, it was expected that there would also be significant inter-individual differences in the amount of fitness they gained. What remained to be seen was how well the four ways of quantifying training load that were being put to the test in the study were able to account for these differences.
I don’t want to get too deep into the mathematics involved. If you’d like to go deeper on your own, open up a web browser and run a Google search on training impulse (TRIMP), of which there are four competing versions. These four methods of calculating TRIMP were the specific tools used by Boone’s team to quantify training load. What’s important to know is that all four of them allow athletes to achieve equal training loads, hence equal levels of predicted fitness, through different combinations of volume and intensity. For example, a cyclist who increases the average intensity but not the volume of his training might end up with the same TRIMP score as a cyclist who does the reverse. The Ghent researchers questioned the validity of this allowance, and the results of their experiment justified their skepticism. While the cyclists did demonstrate improvements in power output at the aerobic and anaerobic threshold and in maximum power, these improvements correlated weakly with changes in TRIMP values.
In addition to tracking TRIMP, Boone’s team calculated the relative amounts of time each athlete spent at low, moderate, and high intensity. Interestingly, this data proved to be a better predictor of fitness gains. In particular, those athletes who spent the least time at moderate intensity exhibited the greatest improvements in power output at the anaerobic threshold. Combining the data on training intensity distribution with the data on training load accounted for almost all of the inter-individual variance in fitness improvement. The authors concluded that the TRIMP formulas should be modified to factor in training intensity distribution.
The lesson for you, as an athlete who cares most about your fitness improvement, is that increasing your training load won’t do you a heck of a lot of good unless you’ve got your intensity balance right. By taking some of the time you’re currently spending at moderate intensity and moving most of it into the low-intensity bucket and the rest into the high-intensity bucket, you will feel and perform better without increasing your training load. And by continuing to apply the 80/20 rule as you add minutes to your weekly training, you will ensure that those minutes aren’t partially wasted.
