There’s a lot of badmouthing going around about the dreaded “grey zone”. Once considered a “no go” zone, the demonized training intensity is presented by many to be an area that will inhibit your aerobic development, and thus something to avoid.
However, like most things in life, it’s not that simple. Let’s begin by discussing what this grey zone really is. In essence, it’s somewhere in between easy and hard. Moderate intensity, you might say. I like the descriptor “comfortably hard”. In a 5 Zone model of exercise intensity, the grey would be Zone 3 into the middle of Zone 4. On a scale of 1-10 on a Rating of Perceived Exertion, it’s a 4-6.
Grey zone is now clearly defined. So why is everyone saying it’s bad?
Much of traditional training theory is based on a Polarization model, meaning that to optimize aerobic development, you should be either going really easy or really hard (with the vast majority of time going easy). So it follows that whenever you’re exercising at a moderate intensity, you’re doing it wrong. Proponents of Polarized training would argue that you’re wasting time at best, and inhibiting your aerobic development at worst.
I believe endurance training is more nuanced than that, and it seems that a lot of modern training philosophies agree. The truth is, as endurance athletes, we need to spend time getting comfortable in all of our zones. I like to compare it to a 5 speed manual transmission. Our bodies and our aerobic system benefit from spending time in all the gears, not just 1st gear and 5th gear.
A classic mistake many newer endurance athletes make is spending most of their time exercising at a moderate-high intensity. Going out for a run and running as hard as you can every time is without a doubt the worst way you can possibly train. This will undoubtedly lead to plateau, burnout, and likely injury. It will eventually inhibit your aerobic development. I believe this is the impetus for all the negative press the grey zone is getting. You most certainly only want to experience it in small doses. But avoid it completely? I think not. As long as you count your time in the “grey zone” towards your higher intensity/hard training volume, it’s great.
I will concede that most of us will get a better aerobic stimulus and subsequently superior adaptations with harder effort (beyond the grey zone). The down side is that the really taxing sessions come at a cost to recovery. Being able to recover quickly so that your body is ready to absorb the next training session is key to a sustainable training program. Therefore, I’m a big proponent of including a nice mix of Zones 3, 4, and 5 in a well rounded training program.
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