January 25, 2023 at 10:00 am EST
How Sleep Impacts Your Workouts

Sleep is a key pillar in the Target100 program and is essential for muscle repair and growth. Lack of sleep has been shown to reduce muscle growth AND increase body fat for a few different reasons we’ll explain.

Muscles contract as a result of biochemical reactions. Whether we are deadlifting heavy weights or sprinting full speed, exercise imposes stress on the body. When our muscles start to shake from being challenged, we are actually creating small tears in our muscles (which explains why exercise sometimes causes physical discomfort). Our body has an amazing ability to respond to increased exercise loads by adapting and building more muscle! But our muscles do not grow immediately as a result of exercising, rather the repair process takes 48 to 72 hours after the workout. Given that sleep is crucial for overall health, here are five reasons to prioritize sleep so you can get the most out of your workouts.

  1. As we sleep our body cycles between different stages of sleep. REM (rapid eye movement) accounts for up to 20-25% of total sleep time in adults. REM sleep provides energy to the brain and restores the mind. Non-REM Sleep, also known as slow-wave or deep sleep, accounts for 40% of total sleep time. Non-REM sleep is essential for muscle recovery and restoration, during this phase your blood pressure drops and your breathing becomes deeper and slower. Your brain is resting so there's more blood supply available to your muscles. Did you know, 95% of the body’s growth hormone is produced during this stage? Growth hormone is a key building block in muscle recovery, once released, it allows your body to ease those aches and pains and supports muscle growth. Sleeping less than 6 hours results in decline in growth hormone secretion. For some athletes, sleeping 7-8 hours is not enough, they need up to 10 hours of sleep! You read that right - you need more than 6 hours of quality sleep a night for muscle repair. The longer a period of sleep, the more time for muscle tissues to regenerate and grow. Try to schedule your workouts with your sleep as a priority.

  2. There are other key hormones that are affected by our sleeping schedule. Lack of sleep has been shown to increase hormones such as ghrelin and cortisol. When these hormone levels are higher, our bodies experience an increase in cravings especially for carbohydrate rich foods. It’s no surprise that after a night with limited sleep, we find ourselves craving sweets and we end up reaching for the pastry and sugary coffee beverage. Higher levels of ghrelin and cortisol also increased body fat storage. So even if you’re eating “clean” and exercising religiously, without sleep, it will be very difficult to reduce your body fat to your goal range.

  3. While some hormones increase due to lack of sleep, we also see reductions in other key hormones such as leptin and testosterone. Leptin is a hormone that is produced by your fat cells, it acts as an appetite suppressant by communicating to our brains when we’ve had enough to eat. While we sleep, leptin levels peak between midnight and dawn, which helps us feel less hungry. Without enough sleep, leptin levels decrease, so our brains seek more energy from food. Lack of sleep reduces testosterone, another key hormone for muscle growth. While we are sleeping, testosterone levels increase to support healing and recovery. Studies have shown that sleep deprivation can cause a significant decrease in testosterone production which can affect men and women. Many people may experience reduced energy, stamina, and strength as testosterone decreases. Paying attention to your hunger and energy levels can help you determine if your lifestyle habits are supporting balanced hormones.

  4. Another key process that occurs while we sleep is the restoration of muscle glycogen. Our muscles and liver store glycogen as a fuel source. When we are active, our muscles break down glycogen quickly to fuel muscle contractions. While you’re sleeping, your body continues to digest carbohydrates from your food and metabolizes them into glycogen. One gram of glycogen in muscle cells can hold three to four grams of water. So as glycogen is replaced, we see an increase in muscle size, and sometimes our weight might increase overnight too! This could feel really discouraging the next day, but once you understand the mechanism, weight fluctuations become less scary. Overtime, the increase in muscle mass will result in increased calorie burning and help you to maintain a healthy weight.

  5. Lastly, lack of sleep increases risk of injury. Studies have shown that you are 2.5 times more likely to sustain a workplace injury if you get less than 5 hours sleep per night, and 1.4 times more likely if you are getting between 6 -7 hours sleep. Lack of adequate rest, reduces reflex times leading to poor judgment. Does anyone remember the BP oil spill that destroyed the ocean? That happened because someone didn’t get enough sleep! When we are sleeping, our brain is removing unwanted waste. During REM sleep, we also see an increase in blood flow to brain cells, which brings more oxygen and glycogen necessary for optimal cognitive performance. So you’ll wake up feeling refreshed and ready to tackle the next day!

Most adults need more than 6 hours of sleep. Napping for 10-20 minutes can increase alertness but napping too long can disrupt nighttime sleep. Plan your workouts based on the sleep you’ll be able to get each night. Create a sleep routine to help train your brain that it’s time to rest, relax, and recover. Schedule high-intensity workouts on days when you plan to get a great night’s sleep, and plan lower-intensity workouts on days when your normal nighttime routine might be disrupted. Too much exercise and too little sleep could result in overtraining and lead to an injury that doesn’t allow you to exercise at all.

To fully harness the power of a good night’s sleep, use Target100 sleep pillar to help you reach your goals. Also up on the blog, we share 5 tips to improve your sleep here and Liz's top picks for products to support a better night's sleep.

This post was written by a fantastic dietetic intern Carmelita Lombera.

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