Exercise is beneficial up to a certain point. When you train your body and subject it to controlled stress, it adapts in a way that makes you stronger, in the case of strength training, or increases your stamina in the case of aerobic exercise. Yet you can push yourself so hard that you exceed your body’s ability to recover. If you do that long enough, it can lead to a syndrome called the overtraining syndrome, a serious manifestation of training too hard.
Overtraining is a bit misunderstood. Most fatigue and lack of motivation that comes from working out too much is overreaching: you push your body too hard and experience fatigue, lack of motivation, and mood changes. However, the effects of overreaching are short-term. Once you rest for a week or so, you will likely recover.
Overtraining is a more extreme form of overreaching where the symptoms are more severe, and recovery is slower. In fact, it may take months to recover from overtraining. In this case, the fatigue is more extreme, and you experience physiological disruptions that trigger extreme fatigue, reduced performance, insomnia, significant mood changes, loss of appetite, and even metabolic disruptions.
It’s not clear what causes overtraining but too much exercise and too little recovery are factors, but what’s happening “under the hood” that causes these extreme changes? Let’s look at some of the theories about what causes overtraining.
Muscle Damage
One possible explanation for what triggers the phenomenon of overtraining is muscle damage. When you work your muscles harder than they’re accustomed to, you break down muscle fibers. With adequate rest, muscles repair the damage, rebuild, and you emerge a bit stronger. But if you keep breaking down muscle fibers without giving your muscles enough recovery time, you get cumulative damage that weakens the muscles and reduces performance. However, this isn’t the full explanation, as it only explains the muscle weakness and reduced performance that happens with overtraining. It doesn’t explain the mood changes and metabolic disruptions that some people experience.
Inflammation
Inflammation gets a lot of airtime these days, as low-grade inflammation contributes to a number of chronic health problems. Could it also be a driving force behind overtraining? As in the previous example, when you overwork your muscles and break down muscle fibers, immune cells rush to the site and release inflammatory chemicals called cytokines. However, these cytokines may have more far-reaching effects on the body. Low-grade inflammation can cause a number of symptoms, including mood disturbances and depression. However, scientists aren’t convinced that the amount of cytokine release correlates well with the symptoms of overtraining. So, it’s probably not the overriding cause but is likely still a factor.
Depletion of Muscle Glycogen
Glycogen is stored carbohydrates that muscles use for energy, especially during high-intensity exercise. Your muscles have a limited capacity to store glycogen and once it’s depleted, muscles fatigue and have a reduced capacity to generate force. Repletion comes in the form of carbohydrates that you take in through diet. If you train aggressively and don’t replenish glycogen adequately between workouts, muscles may experience sustained fatigue and a reduced ability to generate force. However, studies fail to show that aggressively replenishing carbohydrates prevents overtraining. Plus, this theory still doesn’t explain the profound mood changes and fatigue that some people who overtrain experience.
Oxidative Stress
Exercise creates a certain amount of oxidative stress since metabolic processes run at a faster rate during a workout. A certain amount of oxidative stress aids muscle performance and maximizes a muscle’s ability to contract but there is a tipping point where oxidative stress becomes a detriment and muscle performance decreases. The theory is that training too hard increases oxidative stress to the point that it harms muscle function, thereby explaining declines in performance and fatigue.
In support of this idea, some studies show that athletes with symptoms of overtraining have higher levels of markers of oxidative stress. In fact, a 2010 study showed that oxidative stress likely does play a role in the physiological changes associated with overtraining syndrome. Some studies even suggest that markers of oxidative stress might be useful in making the diagnosis of overtraining.
If oxidative stress plays a key role in overtraining, you might wonder whether taking antioxidants would be beneficial since they would reduce the amount of oxidative stress. The downside is some research suggests that taking antioxidants around the time of a workout interferes with some of the positive adaptations to exercise. This applies more to antioxidant supplements than it does antioxidants in dietary form. So, it’s best to get your antioxidants from fruit, vegetables, green tea, and spices instead.
Overtraining and the Central Fatigue Hypothesis
If you over-exercise, your muscles become exhausted, but with prolonged exercise, your central nervous system fatigues too, a phenomenon known as central fatigue. One reason this occurs is that free tryptophan levels in the bloodstream rise and are able to cross the blood-brain barrier in greater quantities during exercise. When tryptophan enters the brain, it causes fatigue and reduces motivation. It also decreases the force of muscle contraction. This is one reason you become fatigued and have to slow down during a workout. However, overtraining can lead to more sustained central fatigue. This hypothesis is attractive because it explains some of the mood changes that people with overtraining syndrome experience.
The Bottom Line
It’s not clear which of these mechanisms play the biggest role in overtraining syndrome. It may be a combination of any or all of these. One thing is clear though. Overtraining can have far-reaching effects on the body and take a long time to recover from. The best approach is to prevent it from happening and that means monitoring for signs such as excessive fatigue, mood changes, a drop in motivation, decreased performance, increased rates of injury, insomnia, and loss of appetite. Training is a healthy kind of stress but only if you do it in moderation and give your body enough time to recover between sessions. Train smart!
References:
- J Sports Sci. 2010 Feb;28(3):309-17. doi: 10.1080/02640410903473844.
- Free Radic Biol Med. 2007 Sep 15;43(6):901-10. doi: 10.1016/j.freeradbiomed.2007.05.022. Epub 2007 May 23.
- com. “4 Theories About Overtraining”
- Sports Health. 2012 Mar; 4(2): 128–138.doi: 10.1177/1941738111434406.
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How Your Body Adapts to the Stress of Exercise & the Importance of Not Overtraining
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