The General Adaptation Syndrome (GAS)
Proposed by Hans Selye in 1936, the GAS describes the "fight-or-flight" reaction to stress. The 3 stages of this GAS include the alarm, the adaptation, and the exhaustion phases. Understanding how these stages affect us during our training is important in designing periodized training programs.
The concept of the GAS is probably familiar to those who participate in heavy resistance training, since it is the basis for the 'overloading' principle. With adaptation to each weight load, there must be a heavier load to stress the muscles for further adaptation to take place.
Exercise And Non-Exercise Stressors
The stress response is the result of circulating adrenaline (epinephrine), which prepares the body for 'fight-or-flight,' characterized by increased arousal, enhanced cardiac output, regulation of blood flow, increased energy substrate mobility and availability, and increased skeletal muscle force production (4). In other words, during the stress response, the body is preparing to move - in a hurry - which is why the line blurs between exercise and non-exercise stress.
The problem with the stress response is that the body sometimes doesn't seem to make a distinction between fleeing from an axe-wielding homicidal maniac, and a job interview.
But it does distinguish between exercise stress and other types. The stress that occurs at the onset of exercise is followed by healthy adaptations. However, this increased 'relaxation response' (increased vagal tone) that occurs after physical exertion does not occur after anxiety (the job interview) or sympathomimetic stimulation (like stimulants; 12).
With exercise, the body gets better at handling stress. With ephedra, it doesn't. That's why you're more likely to experience sympathetic burnout from stimulant intake than from exercise training.
Interestingly though, stress responses differ between individuals. Not everyone experiences terror when public speaking, for example. For those who do, they've got an intact stress response. For those that don't, they probably have an intact stress response too ? they're just not afraid of speaking in public.
But maybe not. If they're suffering from sympathetic burn-out (or parasympathetic overtraining), they might be feeling calm because their body is trying to get "stressed" but can't. Same thing goes for exercise stress or drinking caffeine all day long. If the sympathetic system is tapped out, all the coffee in the world isn't gonna get you stimulated.
Makes sense, right. But I must admit, this is definitely just a hypothesis. Some researchers think it's the case. But others think some people are just more sensitive to the effects of cortisol while others are more sensitive to effects of other stress hormones like epinephrine/norepinephrine.
Either way, since there is no uniform response to stress, research in this field can be sketchy. But, each type of stress does have its own distinctive neurochemical identity.
It has been suggested that the selective processes of so many different stressors may be initiated by transcriptional factors and perhaps by the ratio of release between two neuropeptide/releasing factors (CRF and AVP), which ultimately define the response to any particular stressor (14).
Besides exercise there are a number of personality and lifestyle factors that play a role in the stress response. Some people ("hot responders") experience exaggerated HR and BP response to stressful situations and this has been linked to an increased risk of cardiovascular events (JB studied this at the University of Pittsburgh with a world-renowned Behavorial Medicine laboratory).
Other psychosocial factors, such as a lack of social support can disturb normal autonomic tone and are also associated with an increased risk of cardiovascular events. On the positive side, cardio protective lifestyle factors include marriage, faith, social connection - including dog ownership - are associated with less stress and parasympathetic nervous system activation (12). Here's a handy little chart.
(Curtis, O'Keefe, 2002)
Congestive Heart Failure
Abuse of stimulants
So there are a lot of stressors around us. Interestingly, a well-designed study has demonstrated that those who suffer emotional stress are more likely to experience physical stress and vice versa (13).
Normal peaks and troughs in heart rate variability and cortisol secretion are a sign of a robust response to stress and, more importantly, recovery of that stress response. However, if we accumulate too many stressors, the body may fail to terminate the physiological response once the threat has passed.
This can lead to chronic stress that is accompanied by persistent and inappropriate elevations in cortisol secretion. This leads to immunosuppression, which is associated with the subsequent infection, illness, and even potential long-term psychiatric complications (14).
Eventually this may lead to no stress response. The body's just too tapped out to mount an attack. Alternatively, the system might be producing so many stress hormones chronically that when there's an additional challenge, it can't produce more. The gas pedal is already to the floor.
Overtraining And Mood
Some researchers even believe that chronic stress may eventually lead to "adrenal exhaustion syndrome" (7). This is that inability to mount an adequate stress response we just talked about.
Some of the health complications that occur due to a blunted stress response and altered heart rate variability include higher levels of phobic anxiety and/or panic, depression, and an increased risk of cardiac death (11,15,16). A closer look at overtraining and mood disorder reveals a strong connection between the two syndromes.
A review by Raglin (17) mentioned that aerobic exercise has been found beneficial for anxiety, but after a bout of weight training exercise, anxiety may not be reduced. This may be due to the chronic sympathetic activation that occurs with the sympathetic form of overtraining.
In terms of depression, perhaps chronically elevated concentrations of cortisol lead to the "adrenal exhaustion syndrome" and depression described by Armstrong & VanHeest (7). Some studies have suggested that depression can be triggered by chronic exposure to high circulating concentrations of cortisol.
Surprisingly, some athletes with overtraining exhibit the same stress dysfunction as depressed patients, and there may be a similar dose-response relationship between stressful events and depression as well as between stressful events and overtraining syndrome (7).
To make things more confusing, overtraining can also produce physiological symptoms that mimic depression, like decreased libido and psychomotor retardation (18). Raglin (17) suggests a positive correlation between increased training and elevations in mood disturbances, such that mood disturbance becomes progressively worse as training is increased and mood improves when training is tapered.
However this may only hold true if training is reduced early on in the overtraining syndrome (sympathetic type) since recovery may take as long as a year if training is not reduced before the parasympathetic type kicks in.
If this happens in an elite athlete, it could signal the end of a career. Therefore, because of this potential (and since the signs and symptoms of depression and overtraining share striking similarities) it has been suggested that some of the future pharmacological therapies for overtraining may involve antidepressant medications in order to restore performance (7).
At this point, it's important to note that over training stress and mood disorders are so closely related that the list of stress system dysregulation disorders below could also be a list of the symptoms of sympathetic and parasympathetic types of overtraining.
Of course, full-blown panic and anorexia aren't necessarily going to be associated with overtraining. But I wouldn't be surprised if sympathetic overtraining led to mild panic (i.e. ever gone without eating for a while?) or a reduced appetite (many athletes report reduced appetite when suffering sympathetic overtraining).
(Chrousos & Gold, 1992)
Increased Stress System Activity
Severe Chronic Disease
Chronic Active Alcoholism
Alcohol and Narcotic Withdrawal
Chronic Excessive Exercise
Premenstrual Tension Syndrome
Vulnerability to Addiction
Decreased Stress System Activity
Chronic Fatigue Syndrome
Obesity (hyposerotonergic forms)
Posttraumatic Stress Disorder
Vulnerability to inflammatory Diseases
Several authors propose the idea that both acute stress and melancholic depression are associated with a hyperactive stress response (increased stress hormones, CRH, cortisol and catecholamines, adrenaline and noradrenaline), which results in the consequent inhibition of the thyroid, reproductive (sex hormone) and growth hormone pathways, as well as suppression of the immune system.
Hans Selye described that excessive and chronic stress system activation could cause a state of severe chronic disease (19).
So the question remains, are those who are overtrained just as vulnerable to the serious health issues as those who are just plain chronically stressed? Maybe. If overtraining can result in the deleterious physiological and psychological symptoms that are associated with chronic disease, it could happen.
The only difference, however, is that athletes have a gauge of this stress ? athletic performance. As a result, they must decrease their stress in order to regain form. Those who live with a lifetime of chronic stress may not recognize it until too late. In addition, athletes and those who are physically fit most likely benefit from healthy adaptations from exercise and gain a protective effect against morbidity that the non-fit don't ever get.
However, in terms of mood disorder, unless more research is done in this area, we may never know the numbers of those athletes who have or major mood disorder, some type of mental illness, or disorders associated with stress system burn-out, and the duration of symptoms.
To summarize the connection between overtraining and mood, the concept that the endocrine, immune, and nervous systems are seen as one large system serving integrated functions seems to go largely unrecognized with health professionals. Perhaps we live in a world of "specialization" resulting in experts that are limited to their field of expertise, unintentionally neglecting to treat the body as a highly integrated collection of systems.
For some reason, it is not widely recognized that overtraining syndrome and (major) clinical depression involve very similar signs and symptoms, brain structures, neurotransmitters, endocrine pathways, and immune responses (7). It seems as though most psychologists are unaware of the roles that components of the immune system (cytokines), or intense physical activity, have on the central nervous system.
Likewise, physiologists, coaches, and trainers are unaware of the dynamics between the hormonal and immune systems and how these imbalances create alterations in mood states, potentially affecting the "mental toughness" of their athletes. This point underscores the importance of a strong physiology and psychology background for trainers and coaches.
This week we've covered stress in general, discussed the difference between exercise and non-exercise stress, and talked about some very interesting connections between mood and training status. Next week - what to do about overtraining.
Click here for part three!
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About The Author
Tammy Thomas is a registered dietitian and a certified strength and conditioning specialist (CSCS) who holds a Master's degree in Exercise Science focusing on Nutritional and Exercise Biochemistry. Currently she does training and nutrition writing and consulting for individuals with rheumatoid arthritis and other autoimmune diseases at www.proactivitysupport.com. She can be reached at firstname.lastname@example.org.
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