Athletes who are involved in endurance exercise such as marathons, triathlons, cycling and race walking are subject to tremendous stress due to the volume, frequency, and intensity of training. This can result in non-positive physiological responses, particularly in the neuroendocrine system which is extremely sensitive to stress - not just exercise-related stress, but work, financial, and family stresses as well.
For male athletes, chronic exposure to endurance exercise training could produce alterations such as low basal resting testosterone concentrations. Some men exhibit testosterone concentrations at the extreme low end of normal range that could technically be considered as “normal” concentrations, but they are 40-75% that of normal, healthy, age-matched sedentary men. Clinically this low concentration is expressed as low libido and fertility issues. Muscular mass usually is not affected by this low concentration.
Other important body system alterations associated with chronic exposure to endurance exercise is low bone density expressed frequently as stress fractures or non-logical fractures resulting from mild running or bikes crashes.
X-ray of a 30-year old professional triathlete after a 5 mph bike crash, he has history of previous foot stress fracture. The x-ray shows important low bone density at cortical and trabecular bone.
Alterations in mood, sleep, recovery and appetite have also been associated with this, creating a vicious cycle.
Often, laboratory findings in men with exercise-hypogonadal male condition show low concentrations of Luteinizing Hormone -LH- and high levels of Prolactin and Cortisol. It is well established that low levels of LH and high levels of prolactin and cortisol affect the concentration of testosterone as result of a dysfunction of the hypothalamic-pituitary-testicular regulatory axis.
In my experience as doctor, coach, athlete, husband and father, and supported by research, I would say this condition is a multifactorial condition, with endurance exercise as only a fraction (an important one but not the only one) of the etiologic factors.
Here are other important etiologic factors that can potentially affect the testosterone levels:
Stress
We know that pressures related to work, family, health, social and economic conditions are capable of producing high levels of cortisol and prolactin in sedentary people and these directly impact the regulation of testosterone secretion. For professional and age group athletes, these stresses are additive to that of the chronic endurance exercise, increasing the probability that the regulation of testosterone secretion is affected.
Medication
Antihistaminic, antidepressive, hypertensive and antifungal medications are typically used long-term: antidepresive medication at least 6 months, antifungal and antihistaminic a mean of 3-6 months, and hypertensives for even longer. These medications affect, in different ways, plasmatic testosterone concentration and similarly to stress, could add, synergized or potentiate the effect of exercise in producing a dysfunction of the hypothalamic-pituitary-testicular regulatory axis resulting in lower testosterone plasmatic concentration.
High Altitude
One of the endocrine effects of physical performance at high altitudes – such as high altitude training camps or living at high altitude - included an increase in prolactin and progesterone and decrease in testosterone levels as result of the hypoxic condition. This effect is further increased if the exercise is performed at high intensity.
As you can see, male athletes are exposed to multiple conditions that could affect testosterone regulation resulting in low testosterone concentration. This low concentration can have negative effects on the athlete’s health and social/family life.
In the next article I will review the diagnosis and treatment of this condition.