Have you ever fallen asleep without issue, stayed asleep, with maybe one quick bathroom break, and then woken up only to feel fatigued all day? You look back at your sleep, calculate that you slept for a good 7 or 8 hours, and can’t understand why you are fatigued?
The problem is that you forgot to think about your sleep quality. Almost every set of rules or regulations designed to reduce and manage fatigue I have ever read makes the same mistake. They discount the importance of sleep quality and only focus on sleep quantity.
Some would argue that sleep quality is even more influential than sleep quantity when it comes to predicting fatigue. While I would not go that far, I do think that trying to reduce and manage fatigue by focusing on sleep duration in the absence of considering sleep quality, allows an unacceptable level of risk into the system. For example, Transport Canada is getting ready to implement a rule for railway workers that will allow them to work with just over 5 hours of sleep. Five hours of amazing quality sleep might keep you going for most of the day. I say “might”, because there are quite a few long sleepers out there who are at the higher end of the normal sleep durations (6-9 hours is normal) and reducing a 9 hour sleeper to 5 hours is almost a 45% reduction in their total sleep time. Reducing sleep quantity that much would likely result in fatigue and performance impairments that would compromise safety.
But what if you need the average 7 to 8 hours of sleep and you only sleep for 5:05 hours AND your sleep is terrible quality? According to the Transport Canada rule, you would pass the fitness for duty “test” and you would still have to go to work and perform safety critical activities. There is a tight link between sleep quality and performance and, if you feel that your sleep quality is poor, then your actual performance will be compromised. This means that if someone says they obtained the requisite amount of sleep, but they slept poorly, we should reconsider whether they should be performing safety critical tasks like operating a train.
Supporters of focussing on sleep quantity only will argue that you cannot incorporate sleep quality into fatigue rules and regulations because we cannot predict how well someone will perform based on sleep quality. This is only partly true. The true part is that if we measure sleep quality by looking at the percentage of time we spend in each sleep stage, the direct link to our performance is weak. But what we do know is that the indirect link is strong. It goes like this...brain wave arousals during sleep lead to fatigue, and arousals reduce stage 2, 3 and REM sleep and increase stage 1 sleep. This means that if the normal distribution of the percentage of sleep stages is disrupted by arousals, fatigue will result….and we already know that fatigue decreases performance.
Sleep quantity supporters will then argue that we cannot measure brainwave arousals during sleep to be able to predict fatigue and performance….again, only partly true. Sleep clinics use portable equipment to monitor brainwaves during sleep and measure arousals. The true part is that the equipment is expensive and needs to be applied by a Registered Polysomnographic Technologist. This means it is not a practical solution; and since arousals don’t wake the sleeper, we can’t simply ask the sleeper how many arousals they experienced.
If we look at measuring sleep quality differently, and instead of trying to use objective indicators like sleep stages and brainwave arousals, we use subjective measures, we can predict how well someone will perform. Research has shown that subjective sleep quality is positively linked to subjective fatigue and objective performance and that subjective fatigue predicts objective sleepiness and performance.
This means that if we ask people how well they slept, we can get a good idea of how fatigued they feel, how fatigued they actually are and how well they will perform. In other words, if we apply limits to sleep quality similar to the sleep quantity limits within fatigue rules and regulations, we can reduce the level of risk in the system.
 Sleep quality may be more related to health, satisfaction with life, tension, depression, anger, confusion, fatigue, concentration and driving while sleepy than sleep quantity. See for examples:
(A) Pilcher, J., Ginter, D., & Sadowsky, B. (1997). Sleep quality versus sleep quantity: Relationships between sleep and measures of health, well-being and sleepiness in college students. Journal of Psychosomatic Research, 42(6), 583-596.
(B) Lemke, M., Apostolopoulos, Y., Hege, A., Sönmez, S., & Widerman, L. (2016). Understanding the role of sleep quality and sleep duration in commercial driving safety. Accident Analysis & Prevention, 97, 79-86
 The new rules are published at: https://tc.canada.ca/en/rail-transportation/operating-federal-railway/railway-employee-work-rest-rules-medical-rules/duty-rest-period-rules-railway-operating-employees#Fitness-for-Duty
 Subjective sleep quality predicts objective performance, see for example: Di Muzio, M., Diella, G., Di Simone, E., Novelli, L., Alfonsi, V., Scarpelli, S., Annarumma, L., Salfi, F., Pazzaglia, M., Giannini A., & De Gennaro, L. (2020). Nurses and night shifts: Poor sleep quality exacerbates psychomotor performance. Frontiers in Neuroscience, 4, 1-7.
 See for examples:
(A) Stepanski, E., Lamphere, J., Badia, P., Zorick, F., & Roth, T. (1984). Sleep fragmentation and daytime sleepiness. Sleep, 7(1), 18-26.
(B) Yue, H., Bardwell, W., Ancoli-Israel, S., Loredo, J., & Dimsdale, J. (2009). Arousal frequency is associated with increased fatigue in obstructive sleep apnea. Sleep and Breathing, 13, 331-339.
 See for example: Bonnet, M., & Arand, D. (2007). EEG arousal norms by age. Journal of Clinical Sleep Medicine, 3(3), 271-274.
 See for example: Ünsal, A. & Demir, G. (2012). Evaluation of sleep quality and fatigue in hospitalized patients. International Journal of Caring Sciences, 5(3), 311-319.
 See for example: Nebes, R., Buysse, D., Halligan, E., Houck, P., & Monk, T. (2009). Self-reported sleep quality predicts poor cognitive performance in healthy older adults. Journal of Gerontology: Psychological Sciences, 64B(2), 180-187.
 Kaida, K., Takahashi, M., Åkerstedt, T., Nakata, A., Otsuka, Y., Harantani, T., & Fukasawa, K. (2006). Validation of the Karolinska Sleepiness Scale against performance and EEG Variables. Clinical Neurophysiology, 117(7), 1574-1581.