Sleep is suggested to be one of the most effective recovery strategies available to athletes.
Muscle growth and recovery:
- Involves an inflammatory response to clear away damaged proteins.
- Hormonal signals to activate the replenishment of metabolic substrates (glycogen storage), activate muscle stem cells (satellite cells) to repair damaged fibres, and the synthesis of new proteins.
The main hormones involved in muscle recovery and formation of new proteins are testosterone, growth hormone, and insulin-like growth factor 1. These hormones are mainly released during sleep.
Role of Sleep in Muscle Recovery & Growth
Stages of Sleep
- There are five distinct stages of sleep, nonREM sleep (stages 1-4), and REM sleep (stage 5).
- Metabolic activity is at its lowest point (slowed breathing, low heart rate & blood pressure) during nonREM sleep.
- During nonREM sleep there is an increase in blood flow to muscles which brings oxygen and nutrients to help muscle recovery and a release of hormones.
Muscle Growth & Hormones
Significant molecular changes are required to allow damaged cells to recover or be replaced by new cells involving steps that depend on proliferation, fusion, and differentiation of satellite cells.
Hormonal signals must be accompanied by a signal of muscle hypertrophy because the cells need to increase in volume until the muscle fibres reach their ideal size. Such growth depends on the activation of syntheses pathways and inhibition of protein degradation pathways. Testosterone, growth hormone, and insulin-like growth factor increase the activity of protein synthesis through protein kinase pathways. Thus, are muscle building hormones.
Testosterone released during nonREM sleep works to increase the muscle cross-sectional area of muscle fibres, muscle strength, power, and endurance through an up-regulation in protein synthesis and increased glucose uptake and glycogen synthesis. Testosterone also decreases protein degradation. Other androgens increase satellite cell activation, proliferation, mobilisation, differentiation, and incorporation into skeletal muscles.
Insulin-like growth factor 1 and growth hormone increase protein synthesis, reduces the inflammatory response, and activate satellite cells which after differentiation fuse with hypertrophying muscle fibres. Therefore, driving the overall balance of metabolic pathways to protein synthesis and away from protein breakdown.
Growth hormone is necessary for body restoration and plays an important role in muscle growth and repair. It has been reported that 95% of the daily production of growth hormone is released from pituitary gland in the endocrine system during non-REM sleep.
The Effects of Sleep Deprivation
Studies show that sleep debit favours an increase in body mass due to an increase in hunger and appetite. Studies have shown that extensive and sleep deprivation negatively affects physical recovery and performance. In humans total sleep deprivation is associated with increased secretion of catabolic (muscle breakdown) hormones such as cortisol and changes in secretion of anabolic (muscle building) hormones such as testosterone.
Maintenance of muscle mass reflects a balance between rates of protein synthesis and degradation. The increase in cortisol during sleep deprivation tips the balance towards protein degradation.
Cortisol increases protein degradation pathways and inhibits insulin-like growth factor-1 production. Therefore, sleep debt may modify body composition and potentially impair skeletal muscle health. Detrimental effects of sleep disturbance on exercise recovery include inhibition of muscle glycogen re-synthesis, muscle damage increase and impairment of muscle damage repair.
It is thought that sleep deprivation leads to greater amount of exercise induced damage or that there is an impaired rate of repair after an exercise bout. Due to reductions in insulin-like growth factor-1, testosterone and increases in cortisol promoting protein degradation. Also, can result in an increase in generalised body pain. Hypothesised that disturbed sleep impairs the rate of repair after exercise.
Sleep-deprived individuals may crave unhealthy food and show impairments in glucose sensitivity which may impair glycogen repletion.
Overall, impaired sleep negatively affects growth hormone and cortisol secretion. Sleep deprivation increases pro-inflammatory cytokines which impairs immune system function, impedes muscle recovery and repair. Effects of sleep deprivation include decreased performance, decreased muscle glycogen, reduced maximal strength, reduced time to exhaustion
Most adults require 7-9 hours of sleep per night some professional athletes may need more due to intensive exercise (8-10 hours).
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