Let's start by establishing a couple of basic facts about sleep beginning with sleep cycles and sleep inertia. In each sleep cycle, we go through 4 stages of non-rapid eye movement sleep (N-REM 1-3) to rapid eye movement (REM) sleep. These cycles average about 90 minutes in length. When we wake up in the middle of a sleep cycle, we experience significant levels of sleep inertia because our brains and bodies are expecting 30-60 more minutes of sleep to continue their nightly regeneration process. Psychomotor vigilance task tests bear out the detrimental effects of sleep inertia on central nervous system function and cognition.
A recent Australian study on elite athletes and their sleep habits has shown that they grossly overestimate the amount of sleep they get nightly, to the tune of 1-1.3 hours. The participants estimated that they got 7.7-8.5 hours of sleep per night when in fact, they got 6.7 hours per night on average. The confounding variable that debunks the blanket 8 hours per night is that their HRV data and PSV data was within the margin of error whether the athletes got 6 hours or 8 hours.
Athletes - and non-athletes - should have a goal of a specific number of sleep cycles per night, instead of a number of hours. Patel et al recommend 4-6 sleep cycles, depending on what part of the training year you are in. 4 sleep cycles is about 6 hours of sleep, 6 sleep cycles is about 9 hours. For example, if your average sleep time is 11:00pm and you have workouts at 6:30am, it would be better to wake up at 5:00am than squeezing in as much sleep as possible by sleeping until 6:00am. Add two 10 minute micro-naps later in the day, and you will feel rested and be cognitively and physically more productive.
Sleep is obviously critically important for recovery and regeneration with growth hormone and testosterone being released during each stage 3 N-REM sleep cycle, and also for reducing all-cause mortality. However, in order to maximize each individual night of sleep, we need to change our approach to one that does not increase the risk of waking up in the middle of a sleep cycle and subjecting us to the risks of sleep inertia. Encouraging athletes to accumulate sleep hours over the course of a week or 10 days is a more effective strategy and places less psychic weight on trying to optimize each night of sleep.
From a psychological standpoint, when we overemphasize the idea of "8 hours of sleep or else" - fill in the blank with maladaptive result, we increase the likelihood of creating an all-or-nothing attitude toward sleep in our athletes and ourselves. We should encourage athletes to become more aware of their sleep patterns and give them the tools to take control of their own sleep instead of imposing an arbitrary number of hours on them.