Written by Ben Carlisle
Last updated on: Sep 18, 2022
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The incredibly successful bodybuilder turned actor and politician, Arnold Schwarzenegger, claimed six hours of sleep every night is enough to build muscle. But is this true? This article investigates whether science supports this claim.
“I've always figured out that there 24 hours a day. You sleep six hours and have 18 hours left.... Well, then, just sleep faster, I would recommend.” - Arnold Schwarzenegger
Six hours sleep is not enough to build muscle because it can hinder muscle protein synthesis, which requires rest. It also increases muscle degradation and could therefore result in losing muscle mass. At least seven hours sleep is required for adults to gain muscle.
So, if one of the most famous bodybuilders of all time says he can get by on just six hours sleep, does this apply to everybody, or is he just an exceptional athlete? We take a look at the scientific studies which support or refute the idea six hours of sleep is enough to build muscle.
The CDC recommends adults get at least 7 hours sleep for adequate rest to get through the day ahead. For teenagers they advise sleeping between 8 and 10 hours (1).
What does this mean for muscle growth? The process can be split into three phases: stimulus, recovery, and adaptation. Stimulus refers to the training process, such as resistance exercise. Recovery refers to sleep, rest, and nutrition, while adaption refers to muscle growth (2).
And, because sleep forms part of the recovery process, it impacts and influences both the stimulus and the adaption phases of muscle growth (2). Therefore, there is a strong correlation between quality of sleep and muscle growth or degradation. This means better sleep results in better muscle gains. And poor sleep results in more muscle degradation.
Sleep deficit is an important concept to understand. Sleep deficit (or sleep debt) refers to the discrepancy between the sleep you need and the sleep you get (2). A sleep debt will result in a decrease in muscle protein synthesis and increased muscle degradation. This hinders both the muscle building process and muscle recovery. This increases the likelihood of muscle atrophy (the loss of muscle).
Sleep plays a critical role in any organism’s cellular, systemic, and organic functions. One study showed the response of muscle protein synthesis has a profound effect on muscle hypertrophy (3). Further research investigating the impact of sleep deprivation on muscle growth found acute sleep deprivation reduced muscle protein synthesis by 18% (4). Research has also revealed a link between sleep and the growth of lean muscle . Muscle building depends on sleep. To maximize muscle growth you must get enough sleep (5).
Another study into muscle regeneration in rats found muscular Insulin-like Growth Factor 1 (IGF-1) was reduced when the rats were sleep-deprived (6). IGF-1 is a hormone which helps manage human growth hormone. Increased muscle expression of IGF-I has been found to enhance the effects of training in animals and the results suggest it has a hypertrophic effect (16).
At the same time, sleep recovery restored it to its base levels. The research also found a minimum of seven hours sleep was required to avoid a sleep deficit. This research suggests seven to eight hours sleep is a good minimum target for those who want maximum muscle gains.
Research has found a lack of quality sleep can cause an 18% reduction in muscle protein synthesis, a 21% increase in plasma cortisol and a 24% decrease in plasma testosterone. The study demonstrated even a single night without proper sleep could induce anabolic resistance and promoted a catabolic environment. However, the most important takeaway was, once again, sleeping for a minimum of seven hours was required to avoid these adverse effects (7).
Sleep is also critical for cellular, organic, and systemic functions. Its absence is potentially harmful to health. It changes feeding behaviour, glucose regulation, blood pressure, cognitive processes, and some hormonal axes (8). Further research has found a lack of sleep promotes weight gain and decreases lean muscle mass (9). Daytime testosterone levels are also decreased by between 10 and 15% after a week of only 5 hours sleep per night in young men (10).
One effective strategy to maintain good sleeping patterns is to increase your exposure to bright light during the day, which has led to a 77.5% to 90% improvement in sleep quality (11).
You can also reduce your exposure to blue light in the evenings. The reason for this because exposure to light at night can have the opposite effect of what it can have in the daytime. Light can affect the hormone melatonin, which regulates sleep cycles. This can make it difficult to fall asleep.
Exposure to room light before bedtime was found to delay melatonin release in 99% of individuals in a study on the effects of light exposure in the evening (12). Low levels of light do, however, disrupt the timing of food intake and other metabolic signals, which can cause weight gain (13, 14).
Finally, you should avoid caffeine intake anywhere between 6 and 8 hours before sleep. Research found that caffeine intake three or six hours before bedtime had significant effects on sleep disturbance. If caffeine is taking in the 6 to 8 hour window before bedtime it is likely to make it difficult to fall asleep (15).
It is clear from the research more sleep than six is needed to stimulate muscle growth. Resistance exercise, nutrition, and sleep play a critical role in building muscle mass. Failing to hit your targets in any of these areas will hinder muscle growth. And getting at least seven hours of sleep is important to prevent muscle breakdown and encourage the growth of new muscle tissue.