You’ve seen this motto since you were in high school. You may have even perfected the training and eating part, but what about sleep? How can it affect your body? How many hours do you need?

In the past few years, a drop in the duration of sleep time has become evident in the population, especially in colleges and among those ages 18 – 39. Whether this is from an increase in video games or a boost in online television streaming, it doesn’t really matter. What does matter is that this sleep deprivation leads to impaired cognitive, metabolic, and hormonal functions.

Stop destroying your body by not sleeping enough.

From a metabolic view, almost all human studies show that sleep deprivation favors an increase in body mass. Not the good kind of mass either – rather, an increase in fat mass. These studies show that this is caused by an increase in appetite. You would think that it would be the opposite, since you’re awake more you burn more calories. However, this isn’t the case.  Short sleepers have more time to overeat and also show a preference for fatty foods.

The two hormones that control appetite are leptin and ghrelin. Ghrelin works to stimulate appetite and increases with less sleep.  Leptin works in the opposite way, inhibiting appetite and it is decreased with sleep debt. This causes a ravaging system that actually makes you want to eat more. That’s not the whole story though.

Other hormonal changes induced by a lack of sleep occur in the Hypothalamic-Pituitary-Adrenal axis. This leads to two distinct outcomes: increased secretion of cortisol and significant changes to anabolic hormones. As you probably remember, cortisol causes muscle breakdown, fat deposition and even decreased immune function. To optimize muscle growth and performance you want to reduce your overall levels of cortisol. Now, it’s as simple as sleeping.


Insulin resistance has been reported in young people with sleep deprivation. Furthermore, IGF-1 is rapidly reduced under conditions of sleep deprivation. This creates a catabolic atmosphere. One study showed that subjects on a 14-day diet had similar reductions in body mass as those who slept 5.5 hours per night. However, the subjects who slept 5.5 hours had a much higher loss of muscle mass, as much as 60%. This tells us that muscle mass is regulated by a distinct pattern of hormones and requires sleep to maintain itself.

Sleep plays an important role in muscle recovery, whether the damaged is caused by exercise or injury. Sleep debt damages the muscle by an increase in protein degradation (muscle mass) which helps muscles to shrink, not grow.


The Muscle Clock

Muscle, much like every other tissue in the body, has circadian rhythms. Circadian rhythms are oscillations in biological processes over a 24 hour period. These oscillations are important because they allow you to anticipate changes in the environment.

These rhythms modulate the expression of a huge number of genes in skeletal muscle, many of which aid in muscle recovery and protein synthesis. The rhythms may be synced by cues such as light, time of feeding, and time of activity. However, if the rhythms are disrupted or asynchronous, it can cause major problems. This leads us back to not sleeping enough. When you shift your biological clock by going to bed at 2am instead of the normal 11pm, your body tries to adjust. Now, if you were to continue that pattern it would adjust normally within a week or two, but if you have a sporadic sleep schedule the body can’t resynchronize. It’s like having jet lag all the time. Basically, you’ll feel like shit.

The expression of genes involved in metabolism has been shown to oscillate in muscle. In fact, one of the largest groups of oscillatory genes consists of those in substrate metabolism. Since muscle is a key metabolic tissue, it is important that these be properly synchronized for normal metabolic function.

Testosterone levels follow a circadian rhythm, which bottoms out in late evening and starts to ascend during sleep with a peak in the morning around 8am. Though there appears to be a limit at which sleep duration does not accumulate more testosterone. This limit appears to be 9.9 hours. Importantly, sleep duration and disturbances affect testosterone levels as well as muscle mass and performance. This indicates that sleep plays an active role in the regulation of sex hormone function.

Changes to the circadian rhythm are set once you’re an adult, but during the teen years it undergoes significant changes. This occurs when most teens experience a sleep phase delay. This shift causes teens to feel alert later at night, making it difficult for them to fall asleep at a decent hour. Compounding this problem, most teens start school early which can make it difficult to for them to get the sleep they need, an average of 9.25 hours.

So how many hours do you need? Contrary to what some people believe, you need 7-8 hours of sleep. People may say they only need 5-6, but this just means they aren’t functioning at their full potential. Plus, they will eventually have to make-up that sleep debt or suffer an increased risk of chronic diseases.

There are many sleep-deprived people due to demanding lifestyles or medical conditions (shift-workers, insomnia, and other sleep disorders) or even just being a teenager. Don’t let sleep be the limiting factor for your performance and cognitive goals.

  1. Dattilo, M., H. K. M. Antunes, A. Medeiros, M. Mônico Neto, H. S. Souza, S. Tufik, and M. T. de Mello. “Sleep and Muscle Recovery: Endocrinological and Molecular Basis for a New and Promising Hypothesis.” Medical Hypotheses 77, no. 2 (August 2011): 220–22. doi:10.1016/j.mehy.2011.04.017.
  2. Taheri, Shahrad, Ling Lin, Diane Austin, Terry Young, and Emmanuel Mignot. “Short Sleep Duration Is Associated with Reduced Leptin, Elevated Ghrelin, and Increased Body Mass Index.” PLoS Med 1, no. 3 (December 7, 2004): e62. doi:10.1371/journal.pmed.0010062.
  3. Harfmann, Brianna D., Elizabeth A. Schroder, and Karyn A. Esser. “Circadian Rhythms, the Molecular Clock, and Skeletal Muscle.” Journal of Biological Rhythms 30, no. 2 (April 2015): 84–94. doi:10.1177/0748730414561638.
  4. Sauleda, Jaume, Francisco José García-Palmer, Salvador Tarraga, Andreu Maimó, Andreu Palou, and Alvar G. N. Agustí. “Skeletal Muscle Changes in Patients with Obstructive Sleep Apnoea Syndrome.” Respiratory Medicine 97, no. 7 (July 2003): 804–10.

Brandon Roberts  (@brob21, is a doctoral student in Muscle Biology at the University of Florida. He has worked as a personal trainer for the past 5 years and is part of the Strength and Conditioning staff at the University of Florida.