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How does sleep help recovery from exercise-induced muscle injuries?

Chennaoui, M., Vanneau, T., Trignol, A., Arnal, P., Gomez-Merino, D., Baudot, C., Perez, J., Pochettino, S., Eirale, C. and Chalabi, H., 2021. How does sleep help recovery from exercise-induced muscle injuries?. Journal of science and medicine in sport, 24(10), pp.982-987.

In today’s letter

• Overview of how sleep can affect tissue healing

• Rapid Results = During sleep our bodies go through many hormonal and anti-inflammatory processes to help our systems recover and get ready for the next day

• 3 Reads to check out to further you knowledge about sleep

• Meme of the week: Special tests yay or nay 👍👎?

Aim of study

To add up evidence demonstrating that sleep extension (either napping or increasing nighttime sleep) improved performance, pain sensitivity and hormonal responses, which may be beneficial in accelerating recovery from muscle injury

What is sleep?

• Sleep in most individuals occupies between 20% and 40% of the day, and serves multiple functions in the body and the brain through

• Sleep enhances memory recall, regulates glucose metabolism, reduces mental fatigue, and plays a crucial role in tissue repair, nervous system function, and immune-inflammatory responses.

• During slumber our processes remove toxic waste byproducts in the brain accumulated throughout the day.

• Adults are recommended to sleep for at least 7 hours (8+ is ideal) per night to promote health.

• Sleep in humans is divided into two main phases (and 2 other) :

1. non-rapid eye movement (NREM) dominates the early part of sleep, decreasing in intensity and duration across the sleep period

2. Rapid eye movement (REM) (also known as paradoxical sleep) intensifies and extends towards the end.

• Sleep stages are characterised by specific neurochemical, neurotransmitters and hormones

• Sleep triggers a significant release of:

1. Growth hormone = Regulates growth, cell repair, and metabolism throughout the body.

2. Prolactin = Supports reproductive functions

3. Melatonin = Regulates the sleep-wake cycle and is involved in various biological rhythms and functions, including the regulation of the circadian rhythm

• while downregulating the HPA axis (Neuroendocrine system involved in the body's response to stress and regulation of various physiological processes) and sympathetic nervous system, leading to reduced cortisol, epinephrine, and norepinephrine levels during the night.

• The interaction between sleep and the circadian system strongly regulates immune function, synchronising hormones with pro-inflammatory action and cytokines to initiate adaptive immune responses

• Sleep deprivation (short term or long term) disrupts the balance between catabolic (break down) and anabolic (build up) hormones and increases markers of systemic inflammation.

• Numerous studies have shown that sleep debt may negatively affect cognitive abilities, vigilance, fatigue, mood disorders, and stress, even in young healthy people.

Exercise & sleep

• It is now evident that exercise enhances sleep (if not over trained)

• A systematic review of previous meta-analyses indicates that exercise is linked to significant enhancements in the overall sleep quality, subjective sleep, and decreased time of falling asleep.

• The methodological quality of this review ranged from 36% to 64%, with the quality of evidence assessed as very low.

• The relationship between exercise and sleep is influenced by various factors, including gender, age, fitness level and exercise characteristics such as intensity, duration, time of day, and environment.

• The positive effects of exercise on sleep quality likely involve mood regulation, interactions with circadian rhythms, and physiological effects on thermoregulation, cardiac function, as well as hormonal and immune responses.

• In contrast, endurance athletes and soldiers displaying signs of overreaching/overtraining (high perceived fatigue and decreased performance) have reported a gradual decline in sleep quality, minor decreases in sleep duration, and an increase in injury and lung infections.

Sleep patterns of athletes & military personnel

• Sleep is crucial to optimise athletic performance and to aid recovery.

• Previous research suggests that elite athletes commonly experience poor sleep quality, inadequate sleep duration, and disruptions to their circadian rhythm and sleep patterns due to frequent competitions.

• A systematic review noted a high prevalence of insomnia symptoms among elite athletes, including longer sleep onset times, increased sleep fragmentation, non-restorative sleep, and excessive daytime fatigue

• Multiple sport-specific factors, such as the type of sport, training intensity, timing of training/competition, individual sleep preferences (chronotype), jet lag, and seasonal variations, as well as environmental factors such as sleep environment and use of electronic devices, contribute to the challenges associated with poor sleep

• The specific conditions of training and competition are likely the most influential factors leading to variability in sleep patterns among elite athletes

Sleep and injury risk

Circadian Rhythm = is the body's internal clock that regulates the sleep-wake cycle and other physiological processes over a roughly 24-hour period, influenced by environmental cues like light and temperature

• When the body's circadian rhythms and sleep patterns are out of sync, it can impact athletic performance and increase the risk of injuries.

• Research involving 7576 soldiers (mostly men <35 years), found a correlation between sleep duration and the occurrence of musculoskeletal injuries within the US Army

• In terms of performance, sleep deprivation has been linked to:

1. Decreased reaction time

2. Decreased cognitive function

3. Heightened fatigue levels

• Which contributes to an increase in injury risk among adolescent elite athletes.

• Experimental studies involving approximately 30 hours of sleep deprivation in team-sport athletes have shown various negative effects, including slowed pacing strategies, reduced intermittent-sprint performance, decreased muscle glycogen levels, diminished peak voluntary force and activation, and increased perceptual strain.

• Sleep disturbances have been found to hinder the recovery process, particularly in elite soccer players post-match, leading to impaired muscle glycogen replenishment, delayed muscle damage repair, altered cognitive function, and increased mental fatigue

Injury description

• Numerous intrinsic and extrinsic factors contribute to the occurrence of muscle injuries, particularly in football (soccer) players, these include:

1. Chronological age

2. Previous injury history

3. Poor flexibility

4. Decreased muscle strength or imbalances

• Genetic differences, such as those in the ACTN3 gene encoding the α-actinin-3 protein, as well as variations in proinflammatory cytokines like TNF-α and IL-6, may influence individual responses to exercise-induced muscle damage.

• Certain genetic variations may offer protection against muscle injuries by reducing muscle stiffness.

• Muscle injuries are common in sports, accounting for 30–50% of all injuries in professional football.

• There is a lack of consensus in the literature regarding the classification of indirect muscle injuries

• Typically, Muscle injuries are classified into different grades, with grade 0 lesions showing no alteration of muscle fibre, while grades I, II, and III involve progressively more extensive fibre damage, with grade III resulting in complete rupture

• The recovery time for muscle injuries varies, ranging from a few days for grade 0 injuries to a whole year for grade 3 injuries.

• Diagnosis of muscle injuries relies primarily on clinical assessment but is often supported by radiological examinations.

Muscle regeneration

The language can get a bit complex so I will do my best to simplify, but at the same time give a comprehensive outlook 🤞 😃 

• The regenerative process of skeletal muscles primarily relies on muscle stem cells, known as satellite cells, found in a specific between fibre cell membranes and the basement membrane.

• Following injury, muscle repair progresses through interconnected phases:

1. Fibre necrosis (tissue death *sounds cary but its really normal) and early inflammation

2. Restorative phase

3. Tissue remodeling and maturation.

• Satellite cells are activated by the muscle injury, undergo significant proliferation to generate other cells that help, and ultimately fuse to form new fibres.

• The immune response has many steps, with neutrophils being the initial invaders of the injured area, secreting cytokines to establish a sterile inflammatory environment and recruit additional immune cells, notably circulating monocytes that can change into macrophages

• Other infiltrating cells, including eosinophils and regulatory T cells, also contribute to new muscle fibre creation.

• The resolution of inflammation is an active process involving various mediators such as cytokines and growth factors, particularly IGF-I produced locally by multiple cell types

• The effectiveness of muscle regeneration depends on the type of injury, with alterations in extracellular matrix structure, the inflammatory response, re-vascularization (new blood vessels), and re-innervation (new nerve endings) impacting the process.

• The skeletal muscle, similar to most bodily cells, operates on circadian rhythms, with emerging research suggesting that disruptions in these rhythms can be detrimental to skeletal muscle health.

• A pivotal regulator of the body's internal clock, BMAL1 (a protein), has been identified to help muscle stem cell expansion, thereby influencing muscle regeneration.

• For elite and military tactical athletes, quick and efficient biological responses are crucial for the repair muscle injuries. Sleep and circadian systems serve as vital regulators of hormonal and immune functions, thus potentially playing a huge role in muscle repair.

• While scientific evidence regarding the relationship between sleep and muscle injury recovery remains limited, research in rodent models has showed impaired muscle regeneration following 96 hours of sleep deprivation

• In humans, studies have shown the potential benefits of sleep interventions in promoting an anabolic hormonal activity, increased by sleep extension (napping or increasing the amount of sleep per day) increasing circulating IGF-1 concentrations, even during total sleep deprivation in young healthy men.

• Regarding the impact of sleep interventions on inflammation induced by various environmental stressors, such as sleep deprivation or muscle injuries post-exercise, data in healthy humans remains limited.

• Moreover, studies have highlighted the positive effects of sleep extension or napping on pain sensitivity, which is crucial for recovery from muscle injuries.

• A reciprocal relationship exists between sleep and pain, with pain disrupting sleep and sleep disturbances exacerbating pain, potentially delaying muscle repair by impeding early muscle mobilisation and affecting sleep quality.

• Pain reduction through sleep, along with their additional beneficial effects on alertness, motivation, and mood, may assist people in adhering to rehab post-injury, indirectly helping the recovery process.

Top 3 resources to check out

To learn more about sleep & recovery

1. Optimal sleeping tips from Matthew Walker

   https://www.sleepdiplomat.com/what-is-good-sleep

2. An article about sleep and cognitive impact by yours truly

   https://www.linkedin.com/pulse/can-having-good-night-sleep-make-you-rich-justas-muzikevicius/?trackingId=JLpJmE2VTMOSuvK2uEiCIQ%3D%3D

3. How sleep affects soft tissues (VIDEO)

   https://www.youtube.com/watch?v=pUZvynhxYb4

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