Sleep Loss, Effects on Athletic Performance

Circadian Rhythms

Circadian rhythms, or biological rhythms, are physiological parameters that fluctuate in specific [Page 1348]ways over a 24-hour cycle. Sleep and wakefulness are among those rhythms. Circadian rhythms are genetically and environmentally determined in humans. Each athlete has a preferred sleep schedule that best suits his or her circadian phase. If a circadian preference and sleep schedule are not harmonized, or get out of phase, it will affect the amount and quality of sleep of the athlete.

Overview of Stages of Sleep

The American Academy of Sleep Medicine (AASM) uses a standardized method for describing sleep. This was revised in 2007. The modified stages of sleep and general outline include the following:

• Sleep is analyzed in 20- to 30-second epochs, with each epoch being assigned a single sleep stage.
• Sleep is subdivided into two general states: rapid eye movement (REM) sleep and nonrapid eye movement (NREM) sleep. NREM sleep is further subdivided into four stages.
  • REM: Electroencephalogram (EEG) findings show rapid, low voltage, similar to an active, awake EEG pattern. High-frequency beta waves occur with frequent bursts of REM. Most vivid dreaming occurs during this stage.
  • NREM: This accounts for up to 80% of total sleep time in human adults.
    • Stage 1: In this stage, the brain transitions from wakefulness to sleep or from alpha waves to theta waves. The muscle tone is lost, and the person loses awareness of the external environment. This stage lasts for only minutes, before the person moves on to the next stage.
    • Stage 2: EEG findings are characterized by higher “sleep or theta spindles” and “k-complexes,” which are thought to be associated with arousal. This stage accounts for up to 55% of total sleep and lasts only a few minutes.
    • Stages 3 and 4: (the new AASM guidelines combine Stages 3 and 4). These are characterized by “deep sleep” or “slow-wave sleep.” Delta waves are more pronounced. This is the last and deepest of the sleep stages before REM sleep. If a person is deprived of this stage of sleep, it rebounds once sleep is allowed again, suggesting that this stage is essential to the sleep process.

The true function of REM sleep is uncertain, although some data suggest an important role in memory consolidation. Some data indicate that NREM sleep has an association with the restorative functions of sleep, that is, restoration of alertness and energy. The data indicate that deep sleep is increased in athletes after significant physical effort.

...