Sleep is an intensified anabolic state, accentuating the growth and rejuvenation of the musculoskeletal and immune systems. Hormones such as testosterone and growth hormone are largely released during a good night of sleep. Studies demonstrate that sleep deprivation can reduce anabolic hormone secretion and elevate the catabolic hormone cortisol.2,5 In combination with protein consumption before bed, the anabolic hormones of sleep are essential players in recovery from exercise through maximized muscle protein synthesis. A study from the Netherlands demonstrated that casein ingested immediately before sleep is effectively digested and absorbed, thereby stimulating muscle protein synthesis and improving whole-body protein balance during post-exercise overnight recovery.
Athletic Performance Compromised
Sleep researchers have demonstrated a number of mechanisms by which sleep deprivation can impact athletic performance. In addition to breaking down muscle, the stress hormone cortisol makes your body resistant to glucose metabolism that is otherwise critical to recovery from exercise. Cortisol levels are elevated in a sleep-deprived state.2 Elevated cortisol levels make your body relatively insulin resistant. Insulin is essential to muscle protein synthesis and glucose storage in muscle. Thus, cortisol prevents the restorative effects of insulin on muscle recovery. Essentially, this suggests that sleep deprivation results in a condition very much like type 2 diabetes with insulin resistance. In fact, studies show that chronic sleep deprivation is a risk factor for becoming diabetic.
The weakness and fatigue that occur with sleep debt are due to both nervous system (brain) fatigue and loss of muscle recovery. When the brain is fatigued, reaction times are worsened and a given exercise results in greater perceived exertion. When neuromuscular fatigue occurs, injuries occur on the playing field or in the gym. Neuromuscular reflexes that control joint stability are critical to cutting and throwing in sports. When these reflexes are slowed in combination with muscular fatigue, there is a setup for injuries like a non-contact ACL (anterior cruciate ligament) tear or rotator cuff injury. So sleep-deprived athletes are not only failing to recover, they are putting themselves at risk for catastrophic injury.
Weakened Immune System
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