What Really Happens to Your Body When You Work Out Too Much

Whether you're shopping for new clothes or adding a spicy seasoning to your meal, a little goes a long way. And when exercise is concerned, that's usually the case, too.

It's no secret that exercise releases endorphins, relieves stress, boosts your energy and just generally makes you feel good. But there is a point of diminishing returns — and it's called overtraining.

Overtraining is a condition that occurs when you exercise so much or at such a high intensity so consistently that your body can't recover from that stress. There are different stages of excessive training: overreaching and overtraining syndrome (OTS), according to the Hospital for Special Surgery (HSS).

Overreaching is an early stage of OTS that's easier to reverse, per the HSS, and usually happens when you experience muscle soreness from doing intense back-to-back workouts without sufficient recovery.

If you ignore the symptoms of overreaching and continue to train, you may develop OTS, which can cause more serious symptoms (more on that below). Oftentimes, athletes will misinterpret overtraining symptoms as signs they're simply out of shape, leading them to train longer and harder.

Overreaching and OTS are both associated with symptoms of fatigue, decreased performance, altered mood and/or trouble sleeping. However, overtraining syndrome goes a step further, affecting a variety of your bodily systems.

Unlike the flu or a stomach virus, overtraining syndrome is extremely difficult to diagnose, as there's no one set of criteria used to define OTS, explains Jereme Schumacher, PT, DPT, physical therapist at Bespoke Treatments in San Diego. But there are some common symptoms to look out for.

Here's what really happens when you work out too much.

If you overtrain, you may develop chronic muscle fatigue, according to the American Council on Exercise (ACE). Your muscles and limbs may feel heavy, your heart rate may take longer to recover during training and you may lose agility and speed.

When you continue to push your body to its max workout after workout and when you don't properly refuel, you have what's called low energy availability, per the ACE, which means your body is consistently pulling from its own energy stores (your carbs, proteins and fat) to keep you moving.

As your body pulls from its own nutrient stores, you can't respond productively to the exercise-induced stress. Muscles are broken down during exercise, becoming stronger and more resilient when they repair, Schumacher explains. But without enough fuel or recovery time, there's no way for your muscles to strengthen.

"If you are exercising too much or with poor programming, your body will be unable to properly recover and adapt to the physical stress of working out," Schumacher says.

While it's rare, overexertion may also develop into rhabdomyolysis, a condition that results from the breakdown of muscle fibers, which leak into your blood, according to the American Academy of Family Physicians. If this goes unaddressed, rhabdomyolysis can cause heart issues and even kidney failure.

Exercising frequently throughout the week is totally OK, but make sure you're taking recovery into account, too. Split training (working different muscle groups on different days) is one way you can avoid overexertion, according to the ACE. Mix up your exercise intensity, length and frequency, too.

Even when you do supply your body with some recovery time, OTS makes it difficult to get adequate sleep. Insomnia or restless sleep are common symptoms of overtraining, making it all the more difficult for your body to heal.

Sleep is one of the most important factors in building strength and muscle. While you sleep, your body produces muscle-building hormones, like human growth hormone (HGH), according to the National Sleep Foundation (NSF).

During slow-wave sleep your body also increases blood flow to your muscles, stimulating recovery. In fact, many of the restorative processes for your body occur mostly, or exclusively, during sleep, per the NSF. So, losing a few hours of sleep each night can take a big toll on your body's ability to repair.

OTS and sleep loss can become a vicious cycle. The more you train, the less your body is able to sleep and recover, which ultimately worsens your condition. However, a moderate amount of vigorous exercise each week can actually improve sleep quality, according to the NSF — just make sure you're taking enough days off and fueling properly.

Although research hasn't totally proven that exercising too close to bed will keep you up at night, it's probably smart to keep your heart-spiking workouts a few hours before bedtime, too.

To make matters even worse, OTS can take a toll on your hormones. In general, exercise is calming and helps reduce your levels of cortisol and adrenaline, which are hormones released in times of stress, according to Harvard Health Publishing.

But if you have OTS, you're chronically under stress, with constantly elevated cortisol and adrenaline. Over time, this can cause adrenal insufficiency and depletion, which compromises your body's ability to produce and regulate hormone levels, according to a February 2013 review of research in runners in the ​Journal of Novel Physiotherapies​.

Cortisol serves plenty of functions in the body, helping balance the effects of insulin in breaking down glucose for energy, per the review. Cortisol makes your muscle and fat cells resistant to insulin, causing your liver produce more glucose.

Consistently elevated cortisol levels can lead to insulin resistance over time, according to the University of California, San Francisco. When your cells become more insulin-resistant, your blood will have too much glucose, which your body stores as fat, typically around the abdomen.

For people with periods, this hormonal balance can also disrupt your menstrual cycle. But in the short term, imbalanced hormones can cause agitation and mood swings, according to the ACE. Others may experience unusual irritability or an inability to concentrate.

When you exercise too much, your body may also have trouble getting the energy and nutrition it needs, leading to nutrient deficiencies and medical complications, according to the ACE.

Nutrient deficiency is both a common side effect and cause of OTS, according to the HSS. When you don't fuel your body with enough high-quality carbs, proteins and fats, you can start to experience fatigue, depleted glycogen stores and poor muscle repair, all of which contribute to the chronic exhaustion of overtraining.

Over time, a nutrient deficiency can cause a pretty wide array of symptoms (depending on which nutrients you're lacking), including hair loss, slower healing, bone pain and even altered vision, according to Rush University Medical Center.

Ideally, athletes should get at least 55 percent of their daily calories from carbohydrates with at least 6 to 12 ounces of protein each day, the HSS recommends. However, your specific needs will vary depending on your exercise habits.

Consulting a doctor or dietitian is your best bet when nutrition is concerned. A trained professional can help you establish an ideal meal plan that's suited to your physical activity, while ensuring you're getting all the vitamins and minerals you need to stay healthy.

Chronic overtraining can compromise the immune system, increasing your risk of illness, according to a May 2017 study in the ​Journal of Applied Physiology​. When you overtrain, your body focuses on repairing the damage done by your training, so your overall immunity drops.

After you exercise, your body experiences a window of immunodepression, according to the ​Journal of Applied Physiology​ study, leaving you more vulnerable to infection. If you train again while your immune system is still in this depressed state, you widen the window of potential infection.

It's crucial to prioritize the health of your immune system — for your workouts and beyond. Getting plenty of sleep and rest after exercise is the best way to restore your immune function after training, according to the above-mentioned study.

Ultimately, overtraining doesn't look one way. What causes OTS symptoms in one person may not affect another as strongly, according to Mathew Forzaglia, certified personal trainer.

"Certain types of athletes train two times a day. Some people can handle that volume," he says. "If someone is new to working out or only has been at it a year or so, I would say they are more prone to overtraining. People want to do too much too soon, thinking it will help them faster, but when it comes to working out, less is more."

Even athletes who train more than once per day will typically either alternate between muscle groups or between strength, cardio and mobility sessions to give their body a break. Usually each session will be a quick one, too, rather than two hours-long workouts.

Generally, overtraining occurs when you increase your training frequency or intensity too quickly. Or, if you exercise with too much resistance for prolonged periods of time, according to the University of New Mexico.

Varying workout intensity can help you avoid overtraining, says Carolina Araujo, certified personal trainer. While you may love your HIIT sessions, alternating with more gentle forms of exercise, like yoga or walking, is wise. You can also incorporate activities that promote recovery, including stretching and foam rolling.

You should also take a closer look at your training regimen and make sure you're including recovery days, especially between intense workouts.

Although there's no set number of rest days everyone needs, Araujo recommends taking one recovery or rest day for every three exercise days. Ideally, these exercise days will vary in intensity and modality, too. Those newer to exercise should go for a rest day every two training days to ensure proper recovery.

Working with a trainer or coach is another great way to prevent OTS, Forzaglia says. A trained professional will know how to vary intensity from one day to the next and may also be qualified to give you some nutritional insight.

If you think you may be experiencing overtraining syndrome, ease off your workout routine and consult a doctor to find out what steps you can take to repair and recover.