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Our bodies are designed to receive roughly six to eight hours of quality sleep per night, and skimping on those hours cannot only negatively affect your mood, energy level and alertness, it can also negatively affect your weight-loss results.

While you sleep, your body works to repair muscles that were damaged during your workouts. Exercise, especially weight lifting, puts stress on the muscles, which causes the muscle fibers to tear.

Just like when broken bones heal, muscles becomes stronger than before, which is why you see improved strength over time. (They also heal more tightly and compactly, which is why stretching is important).

Workouts are when you damage your muscles; sleep is when they heal and become stronger.

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During sleep, the body releases hormones that regulate major functions. When you do not get enough sleep, the secretion of these hormones is changed.

Lack of sleep increases the production of cortisol, known as the stress hormone, which is responsible for your “fight or flight” reaction to all stressors: mental, physical and emotional.

Since it is a survival hormone, cortisol stimulates glucose production and triggers a hunger response in the brain, while at the same time signaling cells to store as much fat as possible — a double whammy for weight loss.

Lack of sleep also lowers leptin levels, which control appetite. The less leptin in your system, the more revved your appetite will become.

When the body lacks sleep, it also has a difficult time metabolizing carbohydrates. This results in high blood-sugar levels, which then increases insulin production. That increase in insulin is a signal to your body to store unused energy as fat.

This increase in appetite at the very least can test your willpower, but most often it causes you to consume excess calories. These calories, combined with your hormones telling your body to store as much fat as possible, are a recipe for weight gain.

People in a state of sleep deprivation over long periods of time not only have a higher risk of obesity, they also have increased chances of diabetes, hypertension and memory loss.

While sleep helps improve the effectiveness of your workouts, the quality of your sleep is improved by the quality of your workouts.

Working out is great for reducing stress, which can cause you to lie awake with racing thoughts. Exercise also releases dopamine, which helps relax the body. According to research, exercise can actually increase the amount of time that you spend in the deepest stages of sleep, which is when your body grows, repairs muscles and tissues, and boosts your immune system.

For best results, don’t work out within three hours of going to sleep. Exercise produces an immediate endorphin rush that can keep you awake, if too close to bedtime.

Kelly Turner is a fitness expert and freelance writer. Contact her on Twitter: @KellyTurnerFit, and Instagram: @KellyTurner26

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