How I’m Redesigning My Life23 min read

I exercise at 4:05 am, I never look at my phone for the first 10 hours of my day, and I stop working at 2:30 PM every single day. This life redesign has completely changed my life. I’ve tried 100s of morning and nighttime routines, read 1000s of academic journals, and, finally, I’ve figured out exactly how to optimize my life for health and productivity. The first step is putting your head upside down in the snow for 30 minutes every morning! Don’t have snow? TOO BAD. Ok, well, not really.

In this post, I’ll show you my daily schedule, which has changed my life. It starts at 4 am and ends at 8 pm. I’ve based this on scientific evidence, world-class experts’ advice, and personal experience. If you don’t know me, my name is Zach and I was a doctor, but now I’m trying to find the softest snow in the world to stick my head into.

4 am – 4:05 am, Wake up

4:05 am – 4:20 am, Exercise in front of a 10,000+ LUX blue/white Light (Bike, Turkish getups, farmer’s walks, jump rope, hip flexor, pigeon, and bar hangs)

4:20 am – 4:35 am, Meditate (alternate 15 mins guided and 15 mins unguided)

4:35 am – 4:45 am, Journal (SW, tracker, plan)

4:45 am – 4:50 am, Affirmations and Visualization

4:50 am – 5:00 am, Read

5:00 am – 5:30 am, Breakfast #1, Cold Shower, Brush Teeth, Make Bed, and Dress

5:30 am – 7:30 am, 1st Deep work block (writing)

7:30 am – 8:00 am, Breakfast #2

8 am – 9 am, walk outside solo (no phone, just me and my thoughts)

9:00 am – 11 am, 2nd deep work (YT Projects)

11:30 Am – 12:30 PM, lunch

12:30 pm – 2:30 pm, 3rd deep work session (Coding Projects)

2:30 pm – 4:30 pm, Exercise (lifting, soccer, massage*, sauna, plunge, run, yoga)

4:30 pm – 6 pm, dinner (TV, family time)

6 pm – 7 pm, read (nonfiction), phone down

7 pm – 8 pm, wind-down (shower, read fiction, only soft red light)

*I have a deep tissue massage weekly.

Let’s start with the morning routine.

The Morning

The first hour of your day sets your day up for failure or success.

I want to maximize a couple of things when I first wake up:

• Circadian Rhythm Chemicals
• Day Planning
• Eating the Frog

Circadian Rhythm

Essentially, your circadian Rhythm tells you when it’s time to wake up and when to go to bed. It does this by increasing certain chemicals (like melatonin, serotonin, and GABA) towards bedtime and other chemicals (like cortisol, dopamine, and glutamate) as you wake up. These chemicals are heavily influenced by light, food, physical activity, and when you go to bed and wake up. Not only does keeping these chemicals in check make it 10x easier to fall asleep and wake up in the morning, but it also makes you healthier.

A non-optimized circadian rhythm can have serious health effects. Night shift workers, for example, show increased rates of several types of cancer, increased incidence of cardiovascular and metabolic disorders, and a higher prevalence of behavioral health and psychiatric disorders.^1-4

4 am – 4:05 am, Wake up

4:05 am – 4:20 am, Exercise in front of a Bright Light (Bike, Turkish getups, farmer’s walks, jump rope, hip flexor, pigeon, and bar hangs)

So, I naturally wake up between 4 and 5 am without an alarm because I’ve worked so hard to optimize my circadian rhythm. The first thing I do is drink some lemon water next to my bed at 4 am. Then, and 4:05 I do some form of exercise for 15 minutes in front of the brightest light I have. This is crucial because:

1. Exercise acts as a “Zeitgeber” or environmental cue for circadian rhythm, acting as a cue to your body to “shift” its circadian rhythm. Specifically, cortisol and other chemicals are released that go to your suprachiasmatic nucleus (SCN) which controls your internal clock. A 2019 study showed that those that exercise earlier, shift their circadian rhythm earlier (earlier wake and sleep time) and those that exercise late shift their rhythm later (later wake and sleep time).⁸ This stuff is so interesting, but I’ll stop after this piece of info, your circadian clock exists not only in your brain, but also in your peripheral tissues like your muscles, liver, and fat cells. When you exercise, these other body circadian clocks also turn on, regulating metabolism and energy levels according to a 2021 study from Nature Communications.⁹ Not to mention better sleep and more morning energy.
2. Light is the most powerful Zeitgeber for regulating your circadian rhythm. But most people don’t understand the actual amount of light required to jump-start your circadian rhythm, and that indoor light is nowhere near enough. Lux is the measurement of light where 1 Lux illuminates 1 square meter of space 1 meter away. Indoor light is about 134 lux, while a bright day outside light is about 130,000 lux, or 1,000 times the brightness of indoor lights. According to the evidence, to actually jump-start our rhythm, we need to have preferably blue (460 – 480 nm) but acceptably white (~450-600 nm) light hitting our retina to signal the SCN to suppress melatonin production at ~10,000+ lux for 15-30 minutes! I use a light meter to make sure I am getting that Lux and put it in front of my phase while I exercise.

Now, individuals have genetically organized chronotypes, or “built-in”  circadian rhythms, that influence when they wake up and go to bed. However, there is emerging evidence that light is such a powerful regulator of circadian rhythm that it can override these built-in chronotypes. There are a couple of studies that show when people with vastly different wake-sleep cycles go camping, for example, after a week or so, all of their circadian rhythms align.

Wake up at sunrise and go to sleep shortly after sunset; this makes sense because it’s how we evolved. Electric light (the only thing that comes even close to hitting those levels of LUX and sunlight wavelength, firelight doesn’t do that or seem to affect circadian rhythm) was only invented 200 years ago, and modern Homo Sapiens (me and you) have been around for over 150,000 years. It makes sense that our brain hasn’t made sense of this artificial light, and it’s throwing our lives all kinda whacky.^9-12

These are the two most important things in my morning routine because they regulate my circadian rhythm, making the rest of my day and going to sleep much easier.

Day Planning

Now, the second most important thing I do in the morning is plan my day.

If you want to change the world, start off by making your bed.”

Admiral William H. McRaven

In the Navy Seals, according to Admiral McRaven, if you don’t make your bed perfectly tight, so the sheets would literally bounce a quarter back up into the air when dropped onto it, you haven’t made it right and would be subject to a physical punishment like becoming a “sugar cookie” where, with all your clothes on, you run into the ocean, then roll around in the sand, and look like a “sugar cookie.”

When you make your bed every morning, and make it properly, Admiral McRaven says you set your self up for the rest of the day with a win. Importantly, it also sets the tone for the day that “you care” and will do everything you can to optimize your inputs into your life.

My favorite part of his book, “Make Your Bed,” is when he noticed that after Saddam Hussein was captured, he had never made his bed. Admiral McRaven would often notice the covers were crumpled at the foot of his cot.

Importantly, every time I do every single one of these things in my morning routine, I am leveling up not only by doing the activity but also by setting a tone for the rest of the day.

4:20 am – 4:35 am, Meditate (alternate 15 mins guided and 15 mins unguided)

4:35 am – 4:45 am, Journal (SW, tracker, plan)

4:45 am – 4:50 am, Affirmations and Visualization

4:50 am – 5:00 am, Read

5:00 am – 5:30 am, Breakfast #1, Cold Shower, Brush Teeth, Make Bed, and Dress

So, after I exercise and get my light. I:

• Meditate for 15 minutes, which is usually a struggle, but evidence shows meditation reduces stress, anxiety, and even blood pressure. I alternate between guided meditation (Waking Up App) and unguided meditation (Insight Timer).
• Journal for 10 minutes, where I brain dump, list my 3 Storyworthy moments of the day before (like chasing a bird with my dog), and list my goals for the day. I also review my monthly goals. At this time I have my one black coffee of the day, my favorite being Bulletproof Original coffee ground myself and made with a Chemex (not sponsored).
• Then, using those daily goals, I repeat two affirmations and visualize my day. I feel too self-conscious to reveal these affirmations to the internet at this time, but I created them from the Miracle Morning book. Then, for visualization, I simply visualize myself being successful in the long-term based on my affirmations and what that actually looks like, and then visualize how today will look when I make it successful (doing the work, exercising, etc.)
• Finally, I read for 10 minutes some nonfiction book that is interesting to me. Currently, I’m reading Antifragile by Nassim Taleb.
• Then, I’ll do my first “reset” of the day by eating yogurt (breakfast #1), taking a cold shower, and getting dressed.

Eating the Frog

If it’s your job to eat a frog, it’s best to do it first thing in the morning. And if it’s your job to eat two frogs, it’s best to eat the biggest one first.

Mark Twain

The last part of my morning routine is to hit the ground running with my most difficult task for 2 hours. I do two Pomodoro sessions using this lovely focus timer (not sponsored) of 50 minutes of work, then a 10-minute break, then 50 minutes of work again.

This is the first of one of my three deep work sessions of the day. Oh yeah, I still haven’t looked at my phone. It’s away on a charger and I won’t look at it until it’s gym time around 2:30. My first deep work session is usually focused on writing. It’s when I’m writing this post!

Mark Zuckerberg, Tim Cook, and Elon Musk all know the importance of eating the frog or working on the hardest task first and have all said in interviews how they focus on completing the most difficult task first thing. Importantly, around this time, about 2 hours after waking up, our brain is at peak performance for difficult tasks.

One study challenged people to do math equations at various times during the day. The peak performance was 2-4 hours after waking up. This is one hypothesis as to why students who wake up early perform better. The early risers wake up ~2-4 hours before the test, allowing them to escape sleep inertia (or that early morning brain grogginess,) while late risers may wake up and immediately go to the test, suffering from sleep ineria.^{13, 14}

The Day

My day schedule is deep work sessions broken up by:

• Eating
• Rest
• Exercise

7:30 am – 8:00 am, Breakfast #2

8 am – 9 am, walk outside solo (no phone, just me and my thoughts)

After my first deep work block, I, finishing at 7:30 AM, have my first and biggest break of the day from 7:30 AM to 9:00 PM. It’s 90 minutes, where 30 minutes is spent eating (breakfast #2 as I’m trying to gain weight) and 60 minutes of walking outside.

This is a triple-whammy. Number one, I am spending time in nature and the sun; number 2, I am exercising; and number 3, I am “bored.” Let’s talk about the scientific benefits of each of these things and why walking is so powerful I’m walking always, even when it’s 15 degrees Fahrenheit out and snowing.

• Time in Nature and The Sun
  • Vitamin D: The EPA estimates 93% of american’s lives are spent indoors. With only maybe, one hour a day spent outside. About 1/3rd of all Americans are deficient in Vitamin D. A crucial vitamin for bone health, immunity, and metabolism.¹⁷ One hour of additional sunlight a day can help fight this deficiency. UVB rays from the sun causes vitamin D production, conversion of an inactive form of vitamin D to an active form, and helps transport vitamin D to the right parts of our bodies.¹⁸
  • Nature: 300 minutes in nature a week is optimal, with one study revealing people who spend this time in nature have significantly higher reports of good health or high well-being compared to those who don’t. Also, people who get at least 30 minutes of sunlight a day, earlier in the day, have higher energy levels throughout the day and sleep better.^15,16 Finally, Nature has tons of other magical effects, improved cardiovascular health, attention and memory improvement, decreased anxiety and depression. In fact, Nature is so important, places like Japan are implementing time their as a medical treatment and for urban citizens, called Shinrin-yoku or “forest bathing.” Japanese studies, as referenced in the amazing book, The Comfort Crisis, showed that simply spending 15 minutes in nature drops blood pressure, heart rates, and stress hormones. As well as pumping out 150% more “natural killer” immune cells.²⁰
  • Exercise: I won’t spend too much time here, but after proper sleep, exercise might just be the best thing possible for you. This literally makes you live longer, be happier, and stress less. I exercise about 20 hours a week or 4x the AHA recommended hours (11 hours of cumulative walking/hiking, 8 hours of lifting/yoga/running/soccer, and about 1 hour of my morning exercises). For example, in the Comfort Crisis book, he talks about the Hazda, an indigenous hunter-gatherer tribe in Tanzania, who exercises fast and hard for about 2 hours and 20 minutes a day (14 times that of the average American) and suffer virtually no heart disease or mental health issues (they do have a decreased life expectancy however due to high rates of birth and infant mortality and no access to modern healthcare). I focus on functional fitness with a personal trainer, and every time I walk or hike, I wear a 45-60 lb-pound pack on my back to “ruck” with. Building bone strength and aiming for longevity and injury prevention as opposed to “getting swole.”
  • “Bored time”: Finally, we need some “bored” time. Every time we take out or phone or watch TV we are stressing ourselves out and destroying creativity. Dr. Judson Brewer, a professor of psychiatry at brown university medical school, says, “I wouldn’t pin [stress and addiction] on mobile technology one hundred percent, but I’d say it’s ninety percent due to it.” Steve Jobs wouldn’t let his children use the iPad, and teens today are more stressed and anxious than ever before. In the Comfort Crisis, one study showed the amazing power of “bored time,” a group of people were told to read a phone book for 15 minutes or do what they normally do (go on their phone) and then take a creativity test. The bored people scored significantly higher on creativity exams, and this has been repeated over and over again. There are a couple of amazing things going on when you let your brain rest. One idea is something called “the incubation effect,” where our brain is working on ideas and problems constantly in the background but will only reveal these things when our brain isn’t in an “active” mode. Ever notice how you have the best ideas in the shower, or in the car, or washing dishes, or going for a walk? That’s because you’ve finally given your brain a break to reveal the amazing work it’s been doing in the background. So, I integrate “bored” time into my day every day to let my brain reveal magical ideas, reduce stress, and build resilience.

Ok, that’s a lot of reasoning behind why I walk for an hour, let’s move quickly through the rest of my day.

9:00 am – 11 am, 2nd deep work (YT Projects)

11:30 Am – 12:30 PM, lunch

12:30 pm – 2:30 pm, 3rd deep work session (Coding Projects)

2:30 pm – 4:30 pm, Exercise (lifting, soccer, massage*, sauna, plunge, run, yoga)

My second deep work session is usually something creative. Like continuing to write or working on a YouTube project. I do this because my brain is in tip-top shape after that hour’s walk to really create something amazing.

Then I spend an hour eating lunch and relaxing, not looking at my phone or watching TV (remember bored time is vital, also the food we have access to is so amazing)!

Then, I enter into my 3rd deep work session of the day. Usually, because I feel like I need some social connection and external motivation at this point, I’ll go to a coffee shop or library to work. Also, my creativity and writing muscle is usually worn out by this point. So, I’ll usually work on something more problem-oriented, like editing a YouTube video or coding a website (my current passion)!

Importantly, you’ll notice my deep work sessions are all different. I do that on purpose. I want to do a single task per deep work session, but have variety in my day. I found that when I spent all day just writing, or all day just editing YouTube videos, or all day just coding, it wore me out on those tasks much quicker. Of course, occasionally, I’ll do this to meet a deadline or something like that, but if I want to be able to do this for life and, in the long-term, to take advantage of compounding, I found mixing up my days helps me stay focused.

Then, finally, at 2:30, my day is done. I have had about 6 hours of deep work at this stage, which is HUGE. I changed my life with just 90 minutes of deep work a day for 2 years. If I can keep this up, I am so excited about what I could potentially accomplish in a year.

Ok, so at 2:30, I’m allowed to pick up my phone! I check my messages, reply, and maybe play some music on the drive to the gym, but that’s it. I’ve deleted all social media applications and only post stuff on YouTube, Instagram, or Twitter from my computer using posting software.

Then I’ll exercise from 2:30-4:30, which is currently 3 days a week of lifting weights (2 at the gym and 1 with a personal trainer), two games of soccer, one HIIT run, and two hot power yoga sessions. Usually, after these sessions, I’ll do two cycles of a steam/sauna followed by a cold plunge. And man, oh man, after I come out of that second cold plunge, I feel like a new human. I can’t explain it, but after that 90-minute exercise session and some hot and cold exposure, I literally can’t stop smiling. I feel calm. I feel at peace. And I wouldn’t trade this time for anything.

Finally, the last part of my day is preparing for bed.

The Night

4:30 pm – 6 pm, dinner (TV, family time)

6 pm – 7 pm, read (nonfiction), phone down

7 pm – 8 pm, wind-down (shower, read fiction, only soft red light)

From 4:30 – 6:00, I’ll cook dinner. I watch TV or spend time with my family.

Importantly, I put my phone down at 6 PM to reduce the blue light and reduce my phone time. My whole nighttime routine is optimized to make falling asleep as easy as possible:

• No phone 2 hours before bed (blue light inhibits melatonin)
• No Food 3 hours before bed (hampers proper sleep)
• No exercise 4 hours before bed (releases cortisol)
• No caffeine 12 hours before bed (caffeine can stick in your body at high levels 10 hours after consumption)
• Hot shower 1 hour before bed (decreased body temperature improves sleep quality and speed to sleep)
• Darkness 2 hours before bed (only red light and soft light, to let my melatonin get up there)

I feel like everyone wants to read more, and for good reason. It improves brain function, slows cognitive decline, and helps you learn stuff. I always like to learn stuff.^19-22 However, I would always say “oh I need to read an hour a day,” but never found the time. Now, it’s scheduled, I know what I’m going to read, I know where I’m going to read. Before bed, I switch over to fiction to let my mind fade away into dreamland.

And that’s it! That’s my evidence-based daily routine! Boy am I a nerd…

Caveats

Caveat #1: I’m not working a 9-5: Currently, I’m not working as I recently quit medicine. I have decided on a new job and a new city to live in, but I won’t start that “real job” for about 8 months. Luckily, YouTube provides enough money to cover all of my living expenses until then. However, for now, I want to optimize my time as best as possible with this time off, so this means I don’t have to commute to work or log in, or spend time doing things “assigned” to me.

Caveat #2: I only spend 5.5 days a week on this schedule and sometimes take weeks off. I am not keeping to this schedule every day, usually 5.5 days a week with one day off and one-half day. I take all of Saturday off, watching movies, cooking, or going on day trips, and take the first half of Sunday off, where I usually go for a 4-hour hike and a long breakfast in the morning. Then Sunday afternoon, I plan my week’s tasks and food. I also go on vacations and travel, so occasionally miss a week or even a month. This is perfectly ok for me right now because I’ve been working hard or studying for the past 10 years and want to decompress before my next “real job” starts. But when I am in work mode, I don’t want to waste time. I stick to this schedule, usually around 80% of all of my days, so ~280 days a year.

Caveat #3: I don’t always wake up at 4 AM. Because I want to wake up naturally, I never set an alarm but always wake up between 4 and 5 AM because I’ve got my routine so organized. When I wake up at 5 AM, I push everything back an hour and remove one hour from my third deep work session. I always go to bed at the same time. This is a major key.

How to use this in your life:

Now, if you want to mimic this routine, I think the morning routine is the most powerful one for your day. If you can wake up just one hour earlier and exercise, meditate, journal, plan your day, and read, it can revolutionize your life. The next most powerful thing, if you have a 9-5, is to try and identify 90 minutes a day that you can dedicate to something you are passionate about. The best time to do this is in the morning.

So, maybe you wake up at 5:30 AM instead of 8 AM, spend the first hour exercising, meditating, journaling, planning, and reading, and spend the next 90 minutes on deep work on something you care about before taking an hour to get ready and go to work. This will be hard but can change your life. It’s changed mine. It’s how I started this YouTube channel while spending 60 hours a week in medical school, studying, or in the hospital. However, as I outlined above, this daily routine in the past year has completely leveled up my life. I’ve accomplished what would usually take me 2 years to accomplish (like writing a book) in 2 months, am healthier than I’ve ever been, and am happier than I have ever been. I’m not drinking alcohol for 2025 for the main reason that it throws this routine out of whack.

I know my days become my weeks, which become my years, which become my life.

The difference between an amateur and a professional is in their habits. An amateur has amateur habits. A professional has professional habits.

Steven Pressfield (The War of Art)

Good luck! Let me know how it goes. Thanks for reading.

Zach

Work Cited

1. Haim, A. & Zubidat, A. E. Artificial light at night: Melatonin as a mediator between the environment and epigenome. Philos. Trans. R. Soc. B 370, 20140121 (2015).
2. Fonken, L. K. & Nelson, R. J. Endocrine effects of circadian disruption. Ann. Rev. Physiol. 78, 109–131 (2016)
3. Bedrosian, T. A. & Nelson, R. J. Timing of light exposure affects mood and brain circuits. Transl. Psychiatry 7, e1017 (2017).
4. Hublin, MD, PhD, Markku Partinen, MD, PhD, Markku Koskenvuo, MD, PhD, Jaakko Kaprio, MD, PhD, Sleep and Mortality: A Population-Based 22-Year Follow-Up Study, Sleep, Volume 30, Issue 10, October 2007, Pages 1245–1253, https://doi.org/10.1093/sleep/30.10.1245
5. Hölzel, Britta K., et al. “Stress reduction correlates with structural changes in the amygdala.” Social cognitive and affective neuroscience 5.1 (2010): 11-17
6. Shochat T, Cohen-Zion M, Tzischinsky O. Functional consequences of inadequate sleep in adolescents: a systematic review. Sleep Med Rev. 2014 Feb;18(1):75-87. doi: 10.1016/j.smrv.2013.03.005. Epub 2013 Jun 24. PMID: 23806891.
7. Rechtschaffen, Allan, and Bernard M. Bergmann. “Sleep deprivation in the rat: an update of the 1989 paper.” Sleep: Journal of Sleep and Sleep Disorders Research (2002).
8. Hobson, Ashley, et al. “The effects of morning and evening exercise on circadian rhythms: phase advances and delays.” The Journal of Physiology, vol. 597, no. 20, 2019, pp. 5073-5084. https://doi.org/10.1113/JP278984.
9. Prayag, Arghavan, et al. “Light modulation of human clocks, wake, and sleep.” Scientific Reports, vol. 8, no. 1, 2018, pp. 1–9. https://doi.org/10.1038/s41598-018-22983-1.
10. Wright, Kenneth P., et al. “Entrainment of the human circadian clock to the natural light-dark cycle.” Current Biology, vol. 23, no. 16, 2013, pp. 1554–1558. https://doi.org/10.1016/j.cub.2013.06.039.
11. Stothard, Ellen R., et al. “Circadian entrainment to the natural light-dark cycle across seasons and the weekend.” Current Biology, vol. 27, no. 4, 2017, pp. 508–513. https://doi.org/10.1016/j.cub.2016.12.041.
12. Cajochen, Christian, et al. “Evening exposure to a light-emitting diodes (LED)-backlit computer screen affects circadian physiology and cognitive performance.” Journal of Applied Physiology, vol. 110, no. 5, 2011, pp. 1432–1438. https://doi.org/10.1152/japplphysiol.00165.2011.
13. Randler, C. (2009). Proactive people are morning people1. Journal of Applied Social Psychology, 39(12), 2787–2797. https://doi.org/10.1111/j.1559-1816.2009.00549.x
14. Elder GJ, Wetherell MA, Barclay NL, Ellis JG. The cortisol awakening response–applications and implications for sleep medicine. Sleep Med Rev. 2014 Jun;18(3):215-24. doi: 10.1016/j.smrv.2013.05.001. Epub 2013 Jul 5. PMID: 23835138.
15. White, M.P., Alcock, I., Grellier, J. et al. Spending at least 120 minutes a week in nature is associated with good health and wellbeing. Sci Rep 9, 7730 (2019). https://doi.org/10.1038/s41598-019-44097-3
16. Mead MN. Benefits of sunlight: a bright spot for human health. Environ Health Perspect. 2008 Apr;116(4):A160-7. doi: 10.1289/ehp.116-a160. Erratum in: Environ Health Perspect. 2008 May;116(5):A197. PMID: 18414615; PMCID: PMC2290997.
17. Holick, M. F. “Vitamin D Deficiency.” New England Journal of Medicine, vol. 357, no. 3, 2007, pp. 266-281
18. Bikle, D. “Vitamin D: Production, Metabolism, and Mechanisms of Action.” Endocrinology and Metabolism Clinics of North America, vol. 39, no. 2, 2010, pp. 245–253.
19. Berns, Gregory S., et al. “Short- and Long-Term Effects of a Novel on Connectivity in the Brain.” Brain Connectivity, vol. 3, no. 6, 2013, pp. 590–600.
20. Antonelli M, Barbieri G, Donelli D. Effects of forest bathing (shinrin-yoku) on levels of cortisol as a stress biomarker: a systematic review and meta-analysis. Int J Biometeorol. 2019 Aug;63(8):1117-1134. doi: 10.1007/s00484-019-01717-x. Epub 2019 Apr 18. PMID: 31001682.
21. Wilson, Robert S., et al. “Cognitive Activity and the Cognitive Morbidity of Alzheimer Disease.” Neurology, vol. 81, no. 4, 2013, pp. 314–321.
22. Stanovich, Keith E., and Anne E. Cunningham. “What Reading Does for the Mind.” American Educator, vol. 22, no. 1, 1998, pp. 8–15.
23. https://pmc.ncbi.nlm.nih.gov/articles/PMC6814154/