How does endurance sport affect male fertility

There is a growing body of evidence that exercise affects reproductive function. Most obviously, the effect of excessive exercising on fertility in women is in the form of an absence of a menstrual cycle. In men, however, the effect of overexercising is not immediately noticeable. The first signs usually include changes in morning erection or decreased libido.

Fertility is defined as the ability to reproduce. Duh. Let’s imagine fertility as a spectrum: infertility on one side and optimal fertility on the other. Lifestyle adjustments, better nutrition and less psychological stress, can lead to better fertility, while poor lifestyle, poor nutrition and inability to cope with psychological stressors lead to lower fertility. In men, spermatozoa (sperm cells) are responsible for the fertilisation of the oocyte (the egg). Male fertility is determined by sperm analysis. It includes evaluation of semen volume, sperm concentration, total number and motility of sperm, its vitality and motility etc. 

Spermatogenesis or sperm development of spermatozoa is controlled by hormones produced in the hypothalamic-pituitary-testicular (HPT) axis. Testosterone, along with other hormones, plays a key role in sperm development. The normal function of the HPT axis is critical for sperm development and is sensitive to internal and external factors. It responds to temperature fluctuations, daylight exposure, hunger/food availability and physiological stress factors. 

Physical activity falls under the physiological stressors and therefore could affect the axis, hormone levels and consequently fertility. The extent of the effect of physical activity is highly dependent on the type, intensity, duration and level of physical fitness of the individual. What I am saying is that in most cases trained individuals are better able to handle the stress of physical activity. 

Sedentary life and fertility

Sedentary habits, such as sitting all day at work, or in front of the TV or computer and not engaging in regular physical activity, are not only associated with a general decline in health, but also affect fertility and the offsprings. Weight gain, often associated with a sedentary lifestyle, is an independent risk factor for infertility. It is known that obese men produce sperm of lower quality (lower sperm concentration, poor mobility, DNA damage,…), which can reduce the chances of successful conception. The negative consequences of both a sedentary lifestyle and weight gain can be reversed through physical activity. 

Training and fertility

So far, the link between physical activity and fertility is still unclear. Surprised?  The effect of physical activity on fertility presents an ⌢-curve. Studies reporting moderate levels of physical activity, outdoor activities and weight lifting reported improvements in erectile dysfunction, sperm quality and sperm characteristics. On the other hand, studies of athletes reported deterioration in sperm quality and sperm characteristics. While the majority of the population is in the normal range of physical activity, very enthusiastic individuals might take training to the next level. This is common with endurance sports such as cycling, running and triathlon.

Endurance athletes often experience alterations in the HPT axis, which is primarily expressed as a reduction in testosterone levels, especially when the volume and intensity of training are high. In the study of De Souza, runners with high mileage workloads were compared to the runners with moderate mileage workloads and sedentary controls. High mileage runners (average 108 km/week) had lower total and free testosterone levels and lower sperm quality compared to moderate mileage runners (average ~60 km/week) and sedentary control subjects. Interestingly, only physical activity volume was assessed and the study did not consider energy intake/expenditure. Low food intake or Relative energy deficiency in sport (REDs) may exacerbate the influence of exercise load on fertility. Consequently, they contribute to low testosterone levels and sperm quality, which have the potential to negatively affect fertility capacity. 

High levels of exercise stress can clearly have a  detrimental effect on fertility. The threshold of exercise stress at which the consequences become apparent is highly individual. Trained individuals tolerate higher loads better than untrained individuals, but only in case if their energy intake is adequate. Therefore, we recommend that individuals who have a high endurance training load and wish to preserve their fertility change their training schedule and have training and diet carefully monitored by professionals. Want to know more? Contact us! On the other hand, overweight and sedentary individuals may benefit greatly from moderate activity. In particular, outdoor activities and weight lifting seem to be of great importance for semen quality and could increase the chances of conception

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