I’m really thrilled about how the first part of this series went over. To date, it’s the most-read article on this site, and beat the old one-day record by more than 30%.

Now, I’m not primarily happy because of the site traffic. I’m primarily happy because of how near and dear to me this topic is, so I was stoked that it got a lot of attention. There’s probably an encyclopedia’s worth of training and nutrition articles churned out every day, but sleep seems so esoteric to people. Sure, when they’re not sleeping well they’re worn down and don’t feel great, but how it tangibly affects their training goals is somewhat of a black box.

I’m sure part of the reason is simply that sleep isn’t marketable. 1000 different people can sell 1000 different diet or exercise programs, but there’s not really any way to cash in on saying “sleep more!”

Furthermore, we live in a culture that seems to resent sleep. The amount of time the average adult sleeps per night has been declining for the past few decades, and I can’t count how many times I’ve heard people say that they wish they didn’t have to sleep at all so they’d have more time in the day.

However, that attitude is self-defeating. Just to get back up to speed from the previous article, research has shown that with the same calorie deficit, you’ll lose about the same amount of weight regardless of whether you’re in bed 8.5 or 5.5 hours per night, but the make up of that weight loss is way different. With less sleep, you lose less fat and more muscle with the same amount of total weight loss because of a shift in respiratory quotient (what that means is that less fat is used at rest, so more energy has to come from stored carbohydrate and protein).

Unfortunately, not only does sleep deprivation help keep you pudgy, it also makes it much more difficult to build muscle and recover from training.

This article is pulling heavily from a 2011 review by Datillo et Al. if you’d like to follow along.

1. The anti-anabolic effects of sleep deprivation

Failing to get enough sleep is especially deleterious for your strength and hypertrophy based goals because it reduces circulating levels of two of your primary anabolic hormones – testosterone and IGF-1.

Testosterone directly increases muscle hypertrophy, binding to androgen receptors, going straight to the cell’s nucleus, and increasing transcription and protein synthesis. It also inhibits the activity of other proteins that block the mTOR pathway – the primary cellular pathway of muscle hypertrophy. The effects of testosterone levels within the physiological range on muscle hypertrophy can be overstated (i.e. injecting steroids makes a noticeable difference, but swings within normal healthy range aren’t massively important), and testosterone levels don’t paint the whole picture of someone’s ability to gain muscle in response to training, but there’s no denying that it is an important piece of the puzzle.

IFG-1 is also important for muscle hypertrophy. It also works via the mTOR pathway to increase protein synthesis, and is critical for satellite cell proliferation and recruitment – that means the potential for more nuclei for each muscle fiber, which is the major limiting factor for muscle growth.

So, with sleep deprivation, you have a reduction in muscle protein synthesis via two separate pathways. But it just keeps getting worse from here.

2. Catabolic effects of sleep deprivation

Building on the fact that sleep deprivation decreases testosterone release, testosterone inhibits the effects of myostatin. Myostatin blocks satellite cell proliferation and differentiation (opposite of IGF-1).

Lack of sleep also increases cortisol levels. Acute elevations of cortisol while training are totally normal and expected. However, chronic elevations can cause all sorts of nastiness. Cortisol blocks protein synthesis by inhibiting the activation of the mTOR pathway, and it activates pathways that lead to muscle protein breakdown.

Here’s a handy little picture from the authors summing up what’s going on here:

Worth considering

It may be useful to think of insufficient sleep being similar to the aging process when it comes to its effects on strength, size, and body composition.

1. decreased testosterone

2. decreased IGF-1 and growth hormone

3. increased catabolism

Just thinking aloud (or in text) here, but mechanistically it makes sense. Melatonin does a lot of things in your body beyond promoting sleep, including stimulating growth hormone release, which is crucially important for IGF-1. Melatonin, growth hormone, and IGF-1 all decrease with age. Decreased melatonin release with sleep deprivation could be the first domino setting off the rest of the hormonal cascade. That doesn’t explain the testosterone and cortisol effects, but decreased melatonin production has been implicated in the aging process as a whole. In fact, in mice, swapping the pineal glands (the part of the brain that makes melatonin) from young and old mice substantially prolongs life in the old mice and shortens it in the young mice. Now, don’t think I’m saying that this is absolutely the mechanism behind sleep deprivation’s effects – it’s just an interesting connection worth stewing on (and, I might add, it’s one that gerontologists – scientists studying aging – are stewing on as well). Obviously there are other things going on as well – tidy explanations rarely explain everything going in in a biological system!

So how much should you sleep? Honestly, it depends person to person. There’s no one-size-fits-all answer. Some people simply need to sleep more or less than others, and the amount of sleep you need will vary depending on how hard you’re training and how much stress you’re under. However, my one-size-fits-all answer is this: if you need to wake up to an alarm, you’re not sleeping long enough. Your goal should be to wake up naturally every morning, with an alarm reserved for rare occasions when you NEED to be up earlier or go to sleep later than normal – this should be the exception, not the rule.