In my recent posts I have examined the evidence that there are two closely related sweet spots that matter to athletes: the sweet spot at which the training load is just right to produce peak performance and the sweet spot at which training load is optimal to maximize longevity of both general health and running performance. In those posts I also examined the question of the possible close relationship between these two sweet spots – a relationship suggested by the evidence that similar or even identical processes are responsible for both the effect of training on performance and the effect of training on health. The processes common to both effects come under the general heading of inflammation – the complex set of biochemical processes by which damage to body tissues mobilizes either repair and strengthening; or, if opportunity for recovery is inadequate, leads to chronic inflammation, deterioration in performance and perhaps even to sustained ill health.
Although our genes might play a part in determining the training loads at which these sweet spots are to be found, there is good reason to believe that both of these sweet spots can be moved to a higher level (that is, to a higher training load) thereby improving peak performance and improving health. However to do this we need to understand more about the mechanism of the training effect and about the nature of inflammatory processes. We also need to understand more about monitoring recovery. I touched on these issues last week and will return to them in the future, but meanwhile, it is crucial to consider a third sweet spot: the sweet spot in the mind.
Any exploration of what distinguishes an Olympic gold medal winner from the finalists who did not reach the podium usually comes up against the evidence that there is remarkably little difference in physiology – in measurements such as VO2max or anaerobic threshold or muscle strength or blood hemoglobin levels. We know that all of these peripheral physiological measurements are relevant to athletic performance, but it is difficult to escape the conclusion that the distinction between the champion and the other finalists is more subtle. It is probably to be found in that most subtle and complex of all the components that make up a human being: the human mind.
Recognition of the role of the mind in elite performance has provided a powerful boost for the discipline of sport psychology, but I am afraid that I am almost always disappointed by the writings of sports psychologists. In comparison with the subtle wisdom of a good coach, the simplistic wisdom of many sports psychologists is about as impressive as the simplistic notions of a scientist who tries to explain human behavior on the basis of observation of lab rats, in comparison with the illumination of the human mind provided by a great novelist or playwright. The mind is far too complex to be reduced to simplistic notions such as the power of positive self-talk – despite the fact that there is indeed a grain of truth supporting the power of self-talk. Positive self talk is directed at enhancing self-belief but for many of us, something more subtle than positive self-talk is required to establish strong self-belief.
However, just because the mechanisms of the mind are too complex to be reduced to a few simple principles does not mean that we can safely ignore it. In fact the power of the mind matters not only for the aspiring Olympic champion, but for any competitive athlete and indeed for any recreational runner who simply runs for enjoyment and good health. One of the most intriguing hypotheses regarding the role of the mind of the athlete is Tim Noakes theory of the central governor: a mechanism within the mind (or the brain, since mind and brain are two sides of one coin) that acts to limit physical output so as to limit the risk of damage to the heart and other muscles. While the details of the nature and role of the central governor remains a topic for debate, the core idea that the mind sets limits to exercise tolerance seems to me to be established beyond dispute.
Mind over muscle
A simple but graphic confirmation was provided in a recent study by Macora and Staiano from Bangor University: ‘The limit to exercise tolerance in humans: mind over muscle’ (Eur J Appl Physiol. 2010 Mar 11. [Epub ahead of print]). They required a group of fit young men to cycle at 90% of VO2max (an average power output of 242 watts) until the point of exhaustion; the point at which they could no longer maintain that power output. This point was reached typically after about 10 minutes. They then asked the young men to attempt immediately to produce the maximum power output possible in a five second burst. The peak power achieved during this five second burst was 731 watts, which is more than three times as large as the power output during the sustained test to exhaustion. This of course is no surprise to anyone who has ever sprinted at the end of a marathon, but it clearly documents the fact that our mind sets limits on the power output our body can achieve, according to the expected duration of the demand for effort.
There are many strands of evidence linking the mind to the benefits and harms of training. As I mentioned a few weeks ago, the fitness and health benefit of exercise can be influenced by what you believe about the potential benefits. But perhaps even more relevant to the notion of the sweet spot in the mind is the observation that serial measurements of maximum power during an anaerobic test might be a fairly reliable measure of over-training.
Tests of anaerobic capacity and of the state of mind
The Wingate test is a well recognized test of anaerobic capacity. The participant is required to produce maximum possible power output on a stationary bicycle during a 30 second burst. A power output of 690 watts is typical for the average male and 450 watts for the average female. A very fit male athlete might achieve a value over 1000 watts. This value is usually regarded as a measure of the anaerobic capacity: the ability to produce energy from the ATP and phosphocreatine energy systems. In an over-trained athlete, peak output in the Wingate test falls. For example , former medical director of the British Olympic Association, Dr Richard Budgett reports a study in which the peak power achieved during the Wingate test was reduced from around 1150 watts to 850 watts in over-trained athletes (BMJ 1994;309:465-8). While it is perhaps possible that the loss of peak anaerobic capacity in the overtrained athletes was a direct reflection of loss of biochemical capacity of the muscles, the evidence from Macora and Staiano’s study of the influence of the mind over muscle in which the limit on peak power was set by the mind, makes it far more likely that the decreased anaerobic capacity recorded in over-trained athletes is actually due the protective role of the mind.
Thus if we are to be effective in finding the sweet spot on the crest of the inverted U at which training load is just right for maximum performance and/or health, we also need to understand something about the sweet spot in the mind.
Hormones: long range messengers linking mind and body
As described in last week’s post, it is likely that the key to understanding both the over-training syndrome and the health risks of excessive training is an understanding of the mechanism of inflammation. In addition to the various local chemical messengers such as the molecules known as cytokines that act at the site of muscle damage to mobilize the inflammatory response, two of the body’s major long distance chemical messenger systems play a crucial role in adjusting the overall reaction of the body (and mind) to the stress of heavy training. These two hormone systems are the hypothalamo-pituitary-adrenal system (known for short as the HPA axis) which regulates the release of the hormone cortisol from the cortex of the adrenal gland, and the adrenergic system which regulates the release of adrenaline from the adrenal medulla. The adrenergic system is a part of the autonomic nervous system which plays a crucial role in regulating many visceral functions including the heart rate, as well as engaging in reciprocal interactions with the mind. The HPA axis also regulates many body systems, especially the immune system, and it too engages in important reciprocal interactions with the mind. One of the manifestations of the interaction with the mind is the phenomenon of depression.
Perhaps depression is to the mind what inflammation is to body. It is a response to stress or trauma that mobilizes repair, but it can get out of hand and become a chronic disabling illness. In part this is an analogy, but the overlap is not purely analogy: both the adrenergic nervous system and cortisol play an important role in the response to stress, and both are involved in inflammation and in depression. Depression is associated with increased levels of cortisol and with a failure of the normal feedback mechanism by which the brain regulates the release of cortisol from the adrenal cortex. The interaction between cortisol and depression is reciprocal: the fact that synthetic corticosteroids used to treatment many immune system disorders can cause depression, and that diseases such as Cushing’s disease in which the adrenal gland produces too much cortisol, can result in depression, confirms that corticosteroids can cause depression. However, depression arising from other more overtly psychological causes results in elevated cortical and impaired HPA axis function, illustrating that the arrow of causality can point in either direction.
So it is plausible that depression has evolved, alongside inflammation, as a component of an integrated mechanism for dealing with stress and/or trauma. Neither acute inflammation or depression are pleasant experiences, but provided that they do not get out of hand they are both potentially beneficial. How might depression be beneficial? Perhaps the most direct way is via the inhibition of unnecessary activity. Depression produces slowness and lethargy of both mind and body. For the athlete this scarcely seems a benefit, but as we discussed last week, the most important requirement for obtaining benefit from training is ensuring adequate recovery. A mechanism whereby heavy training induces a state of reduced activity is in fact exactly what is required. Post-training lethargy only becomes a problem when it is excessive and prolonged –it is probably the earliest and perhaps most reliable indicator of the onset of over-training.
Depression has other features: in the early stages there is self-questioning and re-appraisal. Like inflammation, it is associated with increased musculo-skeletal soreness – another early sign of over-training. Humans are social creatures and it is probable that depression serves social roles as well, roles such as the facilitation of empathy and bonding. These various beneficial roles of depression reflect the adaptive side of the condition. Like the manifestations of inflammation, these benign influences can rapidly turn malignant once depression crosses the boundary separating a transient adaptive response from an entrenched illness. The self-questioning is replaced by loss of self-confidence, guilty feelings and pessimism. There is loss of enthusiasm and enjoyment; poor appetite and disturbed sleep. It then becomes a clinical problem requiring treatment.
Profile of Mood States
However, it is the intermediate zone, between the benign adaptive response and overt clinical illness that is of especial relevance to athletes. There is quite good evidence that sub-clinical features of depression are among the earliest and most sensitive indicators of over-training. Lack of enthusiasm for training, lack of competitive edge, lethargy, anxiety, irritability, poor appetite and sleep, and disproportionate soreness in the muscles, are among the most sensitive indicators of over-training. Several studies have shown that the a questionnaire entitled Profile of Mood States (POMS) is valuable in the early diagnosis of over-training – revealing changes in mood that appear well before the deterioration in performance that is the definitive manifestation of the condition. (Budgett R., ‘The overtraining syndrome’, BMJ 1994;309:465-8)
The POMS assessment assigns scores to six aspects of the mental state: Tension, Depression, Anger, Vigour, Fatigue and Confusion. These scores are usually represented with the scores for the six items arranged horizontally across a chart. A healthy fit athlete usually has a marked peak for Vigour and low scores for the other five items, apart perhaps from a mild elevation of tension. So the chart has the appearance of a single iceberg protruding above a fairly calm sea. However, as the over-training syndrome develops the sea becomes more choppy and eventually a ‘reversed iceberg’ appears, with two pronounced peaks corresponding to Depression and Fatigue while Vigour has descended into a trough.
I do not think it is appropriate for an athlete in training to perform regular POMS self-assessments (the full version of the scale has 65 items), but I think it is important to be alert to the emergence of the sub-clinical features of depression Of course, like all physiological markers for over-training, features of depression must be evaluated in light of other circumstances and the individual’s usual state – it is changes from usual that matter. Furthermore, the mind is quite capable of self deception: obsessional determination to complete every planned item in the training program in the face of evidence of accumulating fatigue can be just as dangerous a marker as a lack of enthusiasm for training.
In summary, in avoiding over-training, perhaps listening to the mind is even more important than listening to the body. However, the mind is capable of all sorts of devious tricks by which we can fool ourselves, so listening to the mind is only a reliable guide if we develop the ability to appraise our own mental state accurately.