“Sleep.. chief nourisher in life’s feast,” Macbeth.
In my blog for British Association of Sport and Exercise Medicine, I described improving sport performance by balancing the adaptive changes induced by training together with the recovery strategies to facilitate this, both in the short and long term. 
A recovery strategy which is vital in supporting both health and sport performance, during all stages of the training cycle is sleep.
Sufficient sleep is especially important in young athletes for growth and development and in order to support adaptive changes stimulated by training and to prevent injury. Amongst teenage athletes, studies have shown that a lack of sleep is associated with higher incidence of injury. This may be partly due to impaired proprioception associated with reduced sleep. Sleep is vital for consolidating neurological function and protein synthesis, for example in skeletal muscle. Sleep and exercise are both stimuli for growth hormone release from the anterior pituitary, which mediates some of these adaptive effects.
Lack of sleep can also interfere with functioning of the immune system due to disruption of the circadian rhythm of secretion in key areas of the Endocrine system. Athletes in heavy training, with high “stress” loads and associated elevated cortisol can also experience functional immunosuppression. So a combination of high training load and insufficient sleep can compound to disrupt efficient functioning of the immune system and render athletes more susceptible to illness and so inability to train, adapt and recover effectively. Lack of sleep disrupts carbohydrate metabolism and recently found to suppress expression of genes regulating cholesterol transport. In overreaching training, lack of sleep could be either a cause or a symptom of insufficient recovery. Certainly sleep deprivation impairs exercise performance capacity (especially aerobic exercise) although whether this is due to a psychological, physical or combination effect is not certain.
Sufficient sleep quality and quantity is required for cognitive function, motor learning, and memory consolidation. All skills that are important for sports performance, especially in young people where there is greater degree of neuroplasticity with potential to develop neuromuscular skills. In a fascinating recorded lecture delivered by Professor Jim Horne at the Royal Society of Medicine, the effects of prolonged wakefulness were described. Apart from slowing reaction time, the executive function of the prefrontal cortex involved in critical decision making is impaired. Important consequences not only for athletes, but for doctors, especially for those of us familiar with the on call system in hospitals back in the bad old days. Sleep pattern pre and post concussive events in teenage athletes is found to be related to degree and duration of concussive symptoms post injury. The explanation of how sleep deprivation can cause these functional effects on the brain has been suggested in a study where subtle changes in cerebral neuronal structural properties were recorded. It is not known whether these changes have long term effects.
So given that sleep is essential not only for health and fitness, but to support sports performance, what strategies to maximise this vital recovery process? Use of electronic devices shortly before bedtime suppresses secretion of melatonin (neurotransmitter and hormone), which is a situation not conducive for sleep. Tryptophan is an amino acid precursor in the synthesis of melatonin and serotonin (neurotransmitter) both of which promote sleep. Recent research demonstrates that protein intake before bed can support skeletal and muscle adaptation from exercise and also recovery from tendon injury. Conversely there is recent report that low levels of serotonin synthesis may contribute to the pathogenesis of autoimmune inflammatory disease such as rheumatoid arthritis. This highlights the subtle balance between degree of change required for positive adaptation and a negative over-response, as in inflammatory conditions. This balance is different for each individual, depending on the clinical setting. So maybe time to revisit the warm milky drink before bed? Like any recovery strategy, sleep can also be periodised to support exercise training, with well structured napping during the day as described by Dr Hannah Macleod, member of gold winning Olympic Hockey team.
In conclusion, when you are planning your training cycle, don’t forget that periodised recovery to compliment your schedule should be factored in, with sleep a priority recovery and adaptation strategy.
For further discussion on Endocrine and Metabolic aspects of SEM come to the BASEM annual conference 22/3/18: Health, Hormones and Human Performance
References
Balance of recovery and adaptation for sports performance Dr N. Keay, British Association of Sport and Exercise Medicine
Keay N. The effects of growth hormone misuse/abuse. Use and abuse of hormonal agents: Sport 1999. Vol 7, no 3, 11-12.
Wallace J, Cuneo R, Keay N, Sonksen P. Responses of markers of bone and collagen turover to exercise, growth hormone (GH) administration and GH withdrawal in trained adult males. Journal of Endocrinology and Metabolism 2000. 85 (1): 124-33.
Sleep and sporting performance
Young people: neuromuscular skills for sports performance
“Sleepiness and critical decision making”. Recorded lecture Professor Jim Horne, Royal Society of Medicine 16/11/16
What Does Sleep Deprivation Actually Do To The Brain?
Pre-Sleep Protein Ingestion to Improve the Skeletal Muscle Adaptive Response to Exercise Training
Exercise and fitness in young people – what factors contribute to long term health? Dr N. Keay, British Journal of Sports Medicine
Serotonin Synthesis Enzyme Lack Linked With Rheumatoid Arthritis
“Science in Elite Sport” Dr Hannah Macleod, University of Roehampton, 6/12/16
Dr Nicky Keay 