Perverse Incentives

The Current Version of my Weekly Training Log

Goodhart's law states that "When a measure becomes a target, it ceases to be a good measure." A business owner might want to know how productive her nail factory is. To measure that, she determines how many nails the factory produces in a day. To please their boss, the managers of the factory increase their nail count by producing only very small nails. Unfortunately, these nails are useless. Making the measure into the goal ends up defeating the purpose of the factory.

Quantitating progress is an activity not limited to nail factories. It is something that is part of many different human activities. For example, cyclists do all the time, me very much included as evidenced by the figure at the top of this post. We have a variety of measures for assessing our progress: miles ridden, VO2max, maximum power, and all the rest. What is so insidious is how seductive these measures can be, even when we know we should use them with care. 

For the purposes of this post I'd like to consider the case where I am not training for some specific event but rather riding for its health benefits. How best should I accomplish this? Is it even possible? In a recent post I reviewed a scientific publication that argued that there are no health benefits to exercise. That is a bit of an overstatement of what the authors actually wrote and in any case I would not reverse all my beliefs about the health benefits of exercise based on any single publication. That said, I do think this paper is a good reminder that we don't have nearly as much firm knowledge about the benefits of exercise as we wish we did. Given that necessary skepticism, what should I do? For one thing, I think I should act based on the weight of the evidence, the consensus of the medical community, rather than some philosophical standard of absolute proof.

Based on a very large number of studies carried out over several decades, the consensus of the medical community has been that individuals should participate in at least 150 minutes of moderate intensity aerobic exercise or 75 minutes of vigorous intensity aerobic exercise a week, and that ideally, twice that. There is also a growing consensus that, although 300 minutes of exercise is optimal, most of the health benefits come from the first 150 minutes. According to this, I should worry much more about doing some cycling consistently than hitting that arbitrary 300 minute goal. And yet, I am who I am, and I always want to know "how I am doing" (whatever that means.)  I collect all kinds of training statistics (e.g. measures.) And, not only do I want to know how I am doing, I am happier if I am doing better, so I try to make these statistics look good. That is how my measures become targets.

The above process led my recent obsession with mi/yr (miles ridden during the past year) as recorded in the third column from the right of my Weekly Training Log shown at the top of this post. How did this particular number end up in my Weekly Training Log? It was not in the last version of that log that I posted about back in 2021. It comes from a recommendation from Coach John Hughes, the coach that I follow; specifically, his "riding for health" training plans that I blogged about in 2022. He suggested four different training plans, depending on the athlete's cycling history, and one measure of that history was miles ridden per year. Which plan Hughes recommends is based on a point system, and an athlete gets one point if they ride less than 3.000 miles per year, two points for 3,000 to 3,500 miles a year, and three points if they ride more than 3,500 miles per year. In that 2022 post, I pointed out problems with that measure, but it got stuck in my brain nonetheless and thus I included it in my training log. While I was training for group metric century rides, I didn't pay all that much attention to that measure, but now that I am no longer participating in those rides, I am looking for some kind of goal. That goal became miles per year. Because the ups and downs of my health over the past several years, I have gone above and below that 3,000 mile goal. In 2023, I feel below that goal as a result of problems with my back, and in 2024 my training for metric century rides and my birthday ride brought me back above it. As I searched for meaning after the birthday ride, not allowing myself to fall back below that 3,000 miles per year goal became an obsession.

The miles per year measure could be tracked on a daily basis, but a training plan doesn't have much meaning day by day. I would argue that the smallest unit of a training plan that makes any sense is a week, and so I only calculate miles per year once a week. A weird property of this measure is that it depends on the riding I am doing this week, but it also depends on the riding I did a year and a week ago. Each week I get credit for the new miles I ride that week, but I also lose credit for those miles which are now more than a year old. As a result, I found it easy to stay above 3,000 miles per week at first, but as I started approaching the time of year when, a year ago, I was training first for the Art of Survival Metric Century and then for my birthday ride, the miles that would "fall off the back" each week got larger and larger and so it got harder and harder to stay above the magic number of 3.000 miles.

So at long last, I can explain why my goal of staying above 3,000 miles per year was a Perverse Incentive. Now that I am riding for health it makes no sense to overtrain today to make up for training that I failed to do six months or a year ago. That's one problem. The other is that, as is well known, miles is a flawed measure for how much cycling an athlete has done. It is flawed because 20 miles in the mountains represents much more exercise than 20 miles on flat roads. So, as I was struggling to stay above 3,000 miles per year, it became tempting to favor flat rides over hilly rides. To do so would be perverse.

Let me now turn to a less extreme example, my goal of riding for 300 minutes per week. Because this is such a well established goal of the medical community, it is much less problematic than the Hughes goal of 3,000 miles per year. And yet, it still needs to be used carefully. There are many factors I have to consider as I plan my weekly ride schedule: how I feel, what other tasks I need to accomplish, etc. Imagine I come up with a schedule that fits how tired a feel, involves rides that increase my enthusiasm, and give me time to accomplish some important tasks, but adds up to 298 minutes of riding. Now imagine I could change my schedule to make it add up to 307 minutes of riding, but only by giving up some of these benefits. Obviously the 298 minute schedule is the correct choice, but because it doesn't actually meet the arbitrary goal of 300 minutes, I confess I am often tempted by the 307 minute schedule.

Realistically, how much of a problem do these perverse incentive create? In my experience, not as much as might be feared. Let's consider the example of the Hughes goal of 3,000 miles a year. As perverse as this incentive might have been in theory, I think it was helpful in practice, and therein lies a tale. That tale starts with a question: What is a person to do to prevent a measure from becoming a goal, or at least, to minimize the harmful effects of that? My true goal was to bicycle enough to stay healthy. Therefore, what I had to avoid was to allow my attempt to stay above 3,000 miles per year to push me into unhealthy or demotivating behavior. But if I could use that measure as a motivator towards my true goal (health), I might "beat the devil" so to speak, to violate Goodhart's Law without suffering the consequences. The key reality that made this possible is that the worst thing I could have done for my health was to get discouraged and to stop cycling entirely. For health, it probably doesn't matter if I ride hills or flats, just so long as my heart rate remains above what the medical community calls "light" effort and stays within "moderate" or "vigorous" range, something that I find easy to do even on a flat ride. (A counter-example where this is an issue is my rides on my trainer.) As it happens, deciding between a flat ride and a hilly ride is not so important from a health perspective. What is terribly important is not skipping a ride altogether, something I find very tempting when I am discouraged. And in that case, looking at my progress as measured by miles per year encourages me to do something, a flat ride, a hilly ride (so long as it is not an easy trainer ride) both of which benefit my true goal of better health.