Sleep has often been thought to be an important part of the recovery process and the need for the appropriate amount of sleep has been frequently discussed as an important part of the performance training program. It has been conferred that sleep deprivation is linked to a negative athletic performance.
Sleep deprivation has been associated with:
1) A decrease in growth hormone (GH) activity. During sleep, at later stages (stages 3 and 4) there is an increase in GH activity. GH is associated with growth and development and in the athletic performance world it is more closely associated with muscle development. These stages are where it is thought that we have our most restorative sleep during which there is more muscle relaxation, increased blood flow to the muscles, tissue growth and repair, and energy restoration.
2) Decreased glucose and glycogen storage and synthesis for energy. While we are at rest, the common thought is that our body has the ability to replenish the glycogen in the muscles and the liver improving the stores of energy to synthesize for later use during performance activities.
3) Elevated levels of cortisol (a stress hormone). Elevated cortisol levels have been linked to sleep deprivation. The explanation for this link is not often explained, but the thought is that the lack of sleep increases stress levels. Increases in stress levels and by association, increases in cortisol levels are viewed in a negative way thus contributing to a poorer athletic performance.
Even though these factors have been linked to the negative athletic performances, these physiological factors seem to have a lower impact on athletic performance than do the psychological factors associated with sleep deprivation.
Excluding pharmacological intervention, the two strongest stimuli of GH are exercise and sleep. This seems to go with the thought that appropriate sleep is needed for GH levels to work to the full potential (especially when nighttime GH levels are significantly lower when an individual is sleep deprived). What most people fail to consider is that those people that have lower nighttime GH levels due to sleep deprivation have a higher daytime level of GH activity and typically the level of GH activity over a 24 hour period is the same regardless of sleep. The GH activity during the day was increased to make up for the lack of GH activity at night.
Studies that look at the relationship between sleep and glycogen synthesis do demonstrate a link between the two factors, but are not definitive in determining a critical and direct relationship between sleep and glycogen metabolism. Evidence points toward a more direct relationship between the physiological marker of energy status (in a sense the need for energy use and storage) and glycogen synthesis, but the correlation between sleep regulation and glycogen metabolism may still need to be investigated further.
Cortisol levels are not consistent from study to study when considered in relation to sleep deprivation. It seems as though there are a number of studies that show a lower level of cortisol in those that are sleep deprived and there are a number of studies that show a higher level of cortisol in those that are sleep deprived. Understanding cortisol a little more may explain why this can show either way. Cortisol is a stress hormone that can be more active when an individual is placed under higher levels of stress. For example a higher intensity workout or an important event. One of the effects of cortisol is to heighten awareness in those situations of stress. When the cortisol levels are higher due to the higher stress levels it can be harder to fall asleep due to the heightened alertness which then leads to less sleep and potentially more stress. The cycle then continues of higher cortisol (stress levels) associated with less sleep. For those who have lower stress levels, there can be lower levels of cortisol even in stages of sleep deprivation. Other factors that may be associated with cortisol levels include cortisol’s role in immune suppression, control of metabolism, and the diurnal cycle (24 hour pattern).
Physiologically our bodies adapt to the circumstances that we put them in. Will sleep boost the body’s ability to control the physiological factors that help us improve athletic performance? Yes, but our understanding of this process and the role that sleep deprivation or adequate sleep has needs to be further investigated. For some, the physiological effects of sleep deprivation may have a more pronounced negative effect, but for many, the psychological effects may be the greater culprit of the poor athletic execution.
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