Cortisol, known as the regulator of immune response, is a hormone controlled by the adrenal cortex. This powerful hormone is also known as an adrenalcorticol hormone, a glucocorticoid and hydrocortisone or simply cortisone. Cortisol has a catabolic (muscle breakdown) effect on tissue and is associated with a decrease in anabolic (muscle growth) hormones like IGF-1 and GH. Thus reducing levels of cortisol is ideal for an athlete to achieve tissue growth and positive adaptations to exercise training. Playing many different roles in your body, cortisol can have a negative impact on sleep, mood, sex drive, bone health, ligament health, cardiovascular health and athletic performance, potentially causing fatigue and inflammation. Its primary functions are to increase protein breakdown, inhibit glucose uptake and increase lipolysis (the breakdown of fats). While these effects are undesirable for endurance athletes, they do serve to elevate serum glucose so the brain has fuel to operate during times of physical and emotional stress.
What does an increase cortisol level mean to me?
While cortisol in normal amounts is necessary for proper metabolic function, a chronic elevated cortisol level has adverse effects on your health, mood, body composition and performance. Here's the cycle: elevated cortisol secretion from physical or mental stress causes fat, protein and carbohydrates to be rapidly mobilized in order for you to take action against the stressor. This is sometimes referred to as the 'fight or flight' response. The mobilization of these nutrients in addition to epinephrine and a number of other endocrine hormones allows you to take quick action when presented with stress. During this mobilization, cortisol and adrenaline increase while DHEA (Dehydroepiandrosterone) and testosterone decrease. A chronic elevated cortisol level causes your body to enter a state of constant muscle breakdown and suppressed immune function, increasing your risk of illness and injury while reducing muscle.
How do I know if my cortisol levels are high?
Mood swings, lack of motivation to train, loss of muscle and loss of appetite are all symptoms of an elevated cortisol level. Sound familiar? That's right, overtraining syndrome. If you are not taking steps to modulate your cortisol, you are breaking down your muscle, storing fat and getting sick, all of which don't make for a fast racing season. A more scientific approach is to have your testosterone/cortisol or IGF-1/cortisol levels tested. A suppressed ratio of either IGF or testosterone over cortisol is a sure sign of decreased exercise capacity and overtraining. There is also strong evidence that athletes exercising in a carbohydrate-depleted state experience greater increases in cortisol. Decreased frequency of menstrual periods in women (amenorrhea) has been linked to insufficient energy availability which triggers a stress hormone response and suppresses estrogen and progesterone.
What affects cortisol secretion?
Stress, which includes trauma, infection, disease and exercise, is the primary factor that dramatically raises cortisol levels. Wait a minute, exercise is a stressor? High intensity exercise and prolonged exercise both increase cortisol levels, which remain elevated for about 2 hours following the exercise bout. Repeated exercise without appropriate rest results in chronic elevated cortisol. Additionally, poor diet, inadequate supplementation and lack of rest also play key roles in cortisol secretion.
How does cortisol affect my endurance performance?
It is only with chronic elevated cortisol levels that your performance will suffer, but the effect is dramatic. Excess cortisol suppresses your immune system, producing a greater risk of upper respiratory infections. On top of that, your body will be in a catabolic state -- breaking down muscle and storing fat. In addition to reducing your muscle and getting sick, suppressed testosterone means suppressed recovery. Aerobic and anaerobic muscle fibers need time to repair and recover from hard workouts to improve their capacity to exercise. Elevated cortisol and suppressed testosterone do not allow you to maximize your recovery, leading to slower performance gains. A Swiss study of elite male cyclists suggested that ratios of anabolic to catabolic hormones (ie. testosterone/cortisol or IGF-1/cortisol) may be useful markers for the detection of overtraining. In fact, scientists use this Free Testosterone/Cortisol ratio to evaluate an athlete's training state. They showed a strong relationship between elevated cortisol and decreased testosterone that was most dramatic 30 minutes after endurance exercise to exhaustion. A ratio where cortisol is elevated indicates overtraining, so the modulation of this ratio can be key for those athletes who are susceptible to overtraining. Additionally, amenorrhea in women and low testosterone in men may increase risk for stress fractures.
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