Muscle Tension And Rem Sleep: What's The Connection?

Sleep is an important part of our lives, and within the sleep cycle, there is a distinct stage called REM sleep, which stands for rapid eye movement sleep. During this stage, the eyes continue to move, but the rest of the body's muscles are paralysed, or in a state of reduced muscle tone, to prevent injury. This is when most dreams occur, and the brain activity is similar to that of waking hours. However, some people experience REM sleep behaviour disorder, where they act out their dreams, and their muscles are not paralysed. This can result in minor twitches or complex behaviour, which can cause injury to the sleeper or their bed partner. Understanding the mechanisms behind muscle paralysis during REM sleep is crucial for developing treatments for sleep disorders and improving overall sleep quality.

REM sleep is characterised by temporary paralysis of most of the body's muscles.

During REM sleep, the body experiences temporary paralysis of most skeletal muscles. This paralysis, known as atonia, occurs while the brain remains active and dreaming. The eyes continue to move rapidly, but the rest of the body's muscles are inactive, which may be a safety mechanism to prevent injury during sleep.

Two powerful brain chemical systems are responsible for this paralysis during REM sleep. Research has shown that the neurotransmitters gamma-aminobutyric acid (GABA) and glycine work together to cause REM sleep paralysis by "switching off" the specialised cells in the brain that enable muscle activity. This discovery challenged the previous belief that glycine alone was responsible for inhibiting motor neurons during REM sleep.

During REM sleep, the brain exhibits activity similar to that of a waking brain. Blood pressure rises, breathing becomes irregular, and the eyes move rapidly. The temporary paralysis of skeletal muscles allows us to remain still while dreaming, ensuring we sleep quietly and safely.

REM sleep behaviour disorder (RBD) is a condition where this paralysis does not occur, and individuals act out their dreams. This can range from minor movements like leg twitches to more complex and violent behaviour, such as shouting, punching, and jumping out of bed. RBD is relatively rare, affecting less than 1% of people, and usually develops after the age of 50. It is often associated with other neurological conditions, including Parkinson's disease and Lewy body dementia.

REM sleep behaviour disorder causes people to act out their dreams

During the REM stage of sleep, the body usually experiences temporary paralysis of most skeletal muscles, while the brain remains active and dreaming. This is called muscle atonia, and it allows us to dream safely, preventing us from acting out our dreams physically.

However, for individuals with REM sleep behaviour disorder (RBD), this paralysis does not occur, and they end up acting out their dreams. This can include physical movements and vocalisations during sleep, such as shouting, screaming, punching, kicking, grabbing their bed partner, and jumping out of bed. These movements can be violent and cause serious injuries to the person with RBD and those around them.

RBD is a parasomnia, a sleep disorder that involves unusual and undesirable physical events or experiences that disrupt sleep. It is a rare condition, affecting around 1% of the general US population and 2% of people aged 50 or older. It most commonly affects people over the age of 50, with an average onset age of 61. It is also more common in men, with men and people assigned male at birth being nine times more likely to be affected than women and people assigned female at birth.

The symptoms of RBD can vary in severity, and people with the disorder are often unaware of their actions during sleep. They may only find out about their condition when they wake up with an injury or when informed by a bed partner or roommate. RBD can be diagnosed through a physical and neurological exam, as well as an in-lab video sleep study or polysomnogram (PSG) that records body functions during sleep, such as breathing rate, brain wave activity, and muscle movements.

Treatment for RBD focuses on creating a safe sleeping environment to prevent injuries. This can include removing sharp objects from the bedroom, placing padding on the floor, and sleeping in a separate room if necessary. Medications such as melatonin, clonazepam, and pramipexole may also be prescribed to reduce symptoms.

Facial muscle contractions are a commonly observed feature during sleep

Facial muscle contractions (FMC) are associated with emotional expression during waking hours. FMCs are also associated with emotional dream content during sleep. Recent studies have shown that FMCs occur more frequently and with higher amplitude during REM sleep than in non-REM sleep.

During REM sleep, there is a positive correlation between the various facial muscles. However, the increased activity of these muscles is not simultaneous with REM sleep. This suggests that the higher emotional activity and dream content during REM sleep may be responsible for the increased facial muscle activity.

The findings on FMCs during sleep have implications for understanding sleep disorders such as REM sleep behaviour disorder, as well as for developing treatments for these disorders. For example, people with REM sleep disorder act out their dreams, which can cause serious injuries to themselves and those around them.

Sleep myoclonus is involuntary, nonrhythmic muscle twitching that occurs when falling asleep or during sleep

Sleep myoclonus is a type of involuntary muscle twitching that occurs when a person is falling asleep or during sleep. It is characterised by nonrhythmic and unpredictable jerks or spasms that may affect a single muscle or multiple muscle groups. These movements can include sudden jerking of the arms, legs, or torso, as well as shock-like twitches that last for a brief period. Sleep myoclonus is not a disease in itself but is rather a symptom of several underlying conditions or disorders.

There are two types of myoclonus: physiologic and pathologic. Physiologic myoclonus involves quick muscle twitches followed by relaxation and is common in healthy individuals. Examples include hiccups and "sleep starts", which are jerks that occur as a person drifts off to sleep. On the other hand, pathologic myoclonus involves contractions that begin in one part of the body and spread to other muscles. This type of myoclonus is indicative of an underlying disorder or condition affecting the brain or nerves.

The exact cause of sleep myoclonus is often unknown, but it is usually associated with problems affecting the brain or spinal cord. It can occur on its own or alongside other symptoms of nervous system disorders. In infants and children, sleep myoclonus may be caused by sleep disorders, paediatric periodic limb movement disorder (PLMD), or rhythmic movement disorder (RMD). RMD is often associated with developmental disorders such as ADHD, autism spectrum disorders, and Tourette's syndrome.

For adults, sleep myoclonus may be caused by restless leg syndrome, multiple sclerosis, Huntington's disease, Alzheimer's disease, Parkinson's disease, or Creutzfeldt-Jakob disease. Treatment options for sleep myoclonus include medications such as antiseizure and anticonvulsant drugs, sedatives, 5-hydroxytryptophan, and botulinum toxin (Botox). At-home remedies such as stretching and massaging the affected areas may also help prevent or reduce mild to moderate spasms.

REM sleep is crucial for muscle repair and growth

REM sleep is a distinct stage in the sleep cycle, characterised by rapid eye movements and vivid dreams. But beyond this, it is crucial for muscle repair and growth.

During REM sleep, the body releases growth hormones and initiates protein synthesis, which is a crucial step in repairing and building muscle tissues. These growth hormones stimulate muscle growth, repair tissues, and help the body rejuvenate. The more quality sleep you get, the more growth hormones are released, and the better your muscles recover.

REM sleep accounts for up to 20-25% of total sleep time in adults, dominating the latter half of the sleep period, especially the hours before waking. While non-REM sleep is also important for muscle recovery, it is during REM sleep that the body is able to focus on repairing and building muscle.

To maximise the benefits of REM sleep, it is recommended to get 7-9 hours of quality sleep each night, with around 25% of that time spent in the REM stage. This equates to around 2 hours of REM sleep in an 8-hour period, which is the sweet spot for muscle benefits.

The two-hour window immediately post-exercise is also critical for muscle repair and growth. Getting good quality sleep during this period will enhance muscle repair and growth, ensuring your workouts yield optimal results.

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