So incorrect training can damage your fertility

Sport is healthy. Sport makes you happy, no question. But too much sport can also lead to the desire for children remaining unfulfilled. According to a recent study by the Norwegian University of Science and Technology in Trondheim, women who are very active in sports have a more than three times higher risk of becoming infertile than those who exercise moderately.

“Among all the women, there were two groups who had the most difficulties getting pregnant,” reports study director Sigridur Lara Gudmundsdottir. “These were the women who exercised almost daily and those who did sports to exhaustion.”

In Gudmundsdottir’s study, every fourth woman who exercised to exhaustion was infertile and every tenth woman who exercised daily was infertile. The effect was most noticeable among female athletes under 30 years of age. But even recreational athletes who do not feel at risk should know: Even those who do intensive sports for more than 4 hours a week have a 40 percent lower chance of having children.

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Those who train hard and eat little risk fertility

One reason for this is that a body that is trained too intensively does not have enough energy to prepare for pregnancy at the same time. The other factor for lack of fertility is that many women not only train too hard, but at the same time (whether consciously or unconsciously) eat less and thus do not cover their energy requirements. Keyword: energy availability.

Just 4 hours of intensive sport per week can reduce the chance of pregnancy by up to 40 percent. © Jacob Lund /

“The energy availability is calculated from the energy intake with food minus the energy consumption through training and should normally be around 45 calories per kilogram of fat-free mass per day,” explains Dr. Ulrike Korsten-Reck, nutritionist and head of the Freiburg Obesity Academy.

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In emergency situations the body prevents pregnancy

So if you do a lot of sport and also restrict your diet, you run the risk of not giving your body enough energy. Relative lack of energy in sports means that among experts or even briefly RED-S .

Whenever the energy supply is restricted – whether by excessive exercise, insufficient food intake or, in the worst case, both – the body perceives this as a dangerous condition, switches to survival mode and first shuts down all processes that are secondary to survival so that the heart and brain have enough energy to keep the body alive.

Since pregnancy in this emergency situation would be a danger to the body for mother and child, the body of its own accord ensures that it cannot come to this in the first place: The so-called luteinizing hormone that triggers ovulation is no longer produced and the ovaries neither release an egg nor do they release estrogen or progesterone.

The body switches to “survival mode” when it is under a lot of strain from sport, which impairs fertility. © Jacob Lund /

The permanent absence of menstruation, also known medically as amenorrhoea, is then no longer a sign of pregnancy, but a warning signal that fertility has been affected. And not only that.

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Not only competitive athletes become pregnant less often

“Depending on the duration of this restriction, the normal hormonal regulation weakens,” said Korsten-Reck. Since the low oestrogen level not only makes it difficult to get pregnant, but is also essential for healthy bone metabolism, many women who train too hard also suffer from bone density problems. This also happens because the body uses its own reserves when too little food is supplied to it from outside.

Then it falls back on fat reserves, muscles and unfortunately also on the bone substance.

Several studies show that female athletes with amenorrhea have 10 to 20 percent less bone density than women with a normal menstrual cycle. Although the return of menstruation can cause an increase in bone density, permanent normalisation can never be achieved.

That only applies to competitive athletes, you think? “Not at all”, warns Korsten-Reck. “Of course, in top-class sport the focus is on top performance. But also every woman who does popular sports is at risk.”

It is not only competitive female athletes who strain their fertility, this is also a topic in popular sports. © Jacob Lund /

A too low body fat percentage hinders fertility

So there are many good reasons to supply the body with sufficient energy. Because calorie restriction can be even more dangerous than the hardest training. Even a single month of significant calorie restriction can upset the menstrual cycle. When losing weight, it is therefore all the more important to know what to watch out for.

Alone on BMI because you shouldn’t be orienting yourself. Above all, the body fat percentage is also decisive. Biologist Rose Frisch from the Harvard School of Public Health was the first to link low body fat with infertility and found that women should have a body fat percentage of at least 17 percent in order to be able to become pregnant without any problems. A statement that is still considered relevant worldwide today.

In addition, competitive female athletes have the expertise of a coach or team doctor at their disposal, who warns them in good time before health problems of this kind can occur. Something that amateur sportswomen usually have to do without – and are therefore sometimes even more at risk, simply because they don’t know any better.

Intensive training is one thing, but if the diet does not support the physical effort and the associated energy consumption, the body fat percentage will decrease considerably and cause the problems in question.

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Carbohydrate-rich food promotes ovulation

But there is also good news: Even if it affects you, there’s a way back. Regaining a normal, healthy menstrual cycle is fortunately more food science than rocket science. The International Olympic Committee recommends that athletes take an energy-rich dietary supplement of 300 to 600 calories per day plus at least one day of rest per week.

For intensive training, it is generally advisable to consider what should be added to the diet plan – not what you could eliminate. The quality of the diet is also important. Those who cover their calorie requirements with baked goods and sweets can still have problems. Expert Korsten-Reck advises adequate protein and carbohydrate intake to build up liver glycogen and thus facilitate the pulsation of the luteinising hormone that triggers ovulation.

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Both too much and too little sport leads to infertility

But basically the whole thing is a very reversible system. So if you don’t get your period, you don’t have to worry about not being able to have children. Nevertheless, at the first signs you should act directly and take preventive measures to ensure that the hormonal downregulation does not become chronic.

Don’t worry: moderate sport and fertility go together very well! © Jacob Lund /

The fact that fertility can also return if you cut back on your training and eat a sensible diet is also proven by the large-scale study from Norway cited at the beginning. Most of the women who took part in the study had children in the end despite temporary infertility. On average, even more than the other subjects who had only done moderate sport during the study period.

Study leader Gudmundsdottir: “We assume that both too much and too little physical activity has a negative effect on fertility. Correctly dosed, sport seems to bring benefits”. So it’s like so many things in life: It all depends on the right dose.

3 instant tips for better fertility

  • More sports more calories If you consume less than 2000 calories and do endurance sports, your energy intake is most likely insufficient. Even less than 2250 calories in a day of 2 hours of exercise will increase the risk of missed periods.
  • Pay attention to quality Compare muddy asparagus shortly before the expiry date with a fresh bunch. Not only does the former look bad, it also doesn’t provide you with much energy anymore. With fresh food you do something good for the intestinal flora.
  • Carbohydrates are not enemies In favour of proteins, do not give up carbohydrates. The primary goal of the body is to obtain fuel. If these carbohydrates are lacking, the body forms them from proteins, which are then not available for muscle repair and building. On hard training days, it is essential to think about foods containing starch and sugar!

Sport and pregnancy are not mutually exclusive – if you follow a few rules. Eat enough and not too one-sided, and keep an eye on your energy balance. Then you might soon be pushing a baby jogger in front of you when you run.