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Does Triathlon Training Affect Fertility?

Everyone's got an opinion about training and fertility. We've got the facts.


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For triathletes who’ve spent years focusing on achieving athletic goals, shifting focus to a new goal, like having a baby, can be a bit jarring. That’s even more true if the athlete in question doesn’t find themselves in the family way right away. After all, triathletes are used to a simple formula: get a training plan, follow it to the letter, and execute on race day. When it comes to getting pregnant, however, the right “plan” to follow isn’t always obvious. (Well, OK, maybe some parts are obvious…)

A quick search of “fertility” on triathlon websites and in social media groups will bring up plenty of anecdotes about how changes to an athlete’s training impacted, negatively or positively, their ability to conceive. Often, these stories are presented as proof that changing a bike seat, reaching a specific body fat percentage, or sticking to a certain number of training hours is the answer to becoming a mom or dad.

But in actual fact, understanding how your training might be affecting your fertility is a little more complicated. So we went to Dr. Diana Vaamonde, co-editor of Fertility, Pregnancy, and Wellness as well as Exercise and Human Reproduction, as well as a co-author of numerous studies on the impact of exercise on male fertility, to find out what common beliefs are myths, which ones are based in facts, and, most importantly, what triathletes who want to start a family can do to improve their fertility.

Photo: Getty Images

Does cycling affect sperm count?

Cycling, specifically, has gotten a bad rap when it comes to male fertility. But what does the science say? Does cycling decrease sperm count, or otherwise decrease fertility in male triathletes who spend hours in aero?

“While sperm count is somewhat affected, other parameters related to semen quality are more affected,” Vaamonde said. Sperm morphology (the size and shape of sperm) in particular has been found to correlate to high cycling volume, she said — and that’s important since it’s a factor that’s considered in the evaluation of male fertility. She also notes that sperm DNA fragmentation, which refers to abnormal genetic material within the sperm and can also lead to trouble conceiving, has been shown to be an issue.

But why? There are a few potential reasons, Vaamonde said. A bike seat is a potential cause due to friction, which, she said, “could even also lead to erectile dysfunction and ejaculatory alterations in some cases because of altered blood flow or nerve damage.” However, this is not as widespread as is commonly believed: A 2018 study led by Mohannad Awad at the University of California-San Francisco found that even though cyclists had statistically higher odds of urethral stricture, or narrowing of the urethra, when compared to swimmers and runners, their sexual or urinary functions were no worse.

However, sexual functioning and fertility are not one and the same, and other areas of reproductive function might be affected by training. Research suggests the demands of exercise on the body have some effect on sex hormones and the balance of free radicals and antioxidants in the body, which can affect fertility. Vaamonde said that those effects include:

  • The alteration of sex steroid hormones in endurance athletes. “That, by itself, will have an impact on sperm parameters,” she said. That matters because sex steroid hormones modulate reproductive function, and changes to androgen (like testosterone) levels can affect fertility.
  • Exhaustive endurance exercise can also have a detrimental effect on the gonadal axis, the brain’s switchboard between the hypothalamus, the pituitary gland, and the gonads.
  • Energy imbalance, which can occur when we train without proper fueling and recovery. When this happens, free radicals run rampant in the body, causing a state known as oxidative stress which can damage cells—including those affecting reproductive function.
  • Thermal stress (or excessive heat) is also an issue, Vaamonde said: “An increase in heat may negatively affect sperm in the testes and epididymis.” Heat stress to the testicles—from ambient temperatures, increased core temperature while exercising, and/or constricting clothing or environments—may affect sperm count, motility, and even the sperm’s genetic material. After all, the testes are located outside the body cavity for good reason: the sperm production process requires temperatures lower than the body.
  • “Some researchers have reported increased prevalence of serious forms of varicocele [which is an enlargement of the veins that transport oxygen-depleted blood away from the testicle] in athletes, and also that sports practice seems to worsen the condition.” In severe cases, varicocele can increase scrotal temperature and affect sperm production and quality.

When it comes to men who exercise, though, you need to keep in mind that their training is not the only possible reason for infertility or subfertility. After all, nearly 1 in 7 couples will experience infertility, and they certainly aren’t all training for a triathlon, so if you and your partner have given it the old college try and still haven’t gotten pregnant, talking to a fertility specialist about other potential causes may be a wise move.

Photo: Getty Images

Training and female fertility

One thing to keep in mind is that no two bodies are exactly alike, and what worked for your training buddy when she was trying to get pregnant might not work for you—and that does not mean anything is wrong with you.

There are a lot of factors involved in female fertility, but with regard to how sport impacts it, Vaamonde said that the first thing to consider is whether your cycle is regular. “Any ovulatory disturbances would be of concern,” she said. These disturbances may or may not be related to your training—some women have pre-existing conditions that may be affecting their fertility absent of your training load.

Even if you menstruate regularly, it’s also possible to have anovulatory cycles, which are cycles where you don’t release an egg from the ovaries. Several factors can cause anovulatory cycles, like hormonal imbalances due to hormonal birth control, exercising excessively, experiencing significant stress, or being under- or overweight. The tricky thing is, Vaamonde said, “some women are not even aware, as there may be a bleeding that they mistakenly take for a real menstrual bleeding.” That’s a real problem for women trying to conceive. “If there is no ovulation, there can’t be fertilization and thus no pregnancy,” Vaamonde said. And so, even if you are seeing evidence of a regular cycle, she said it’s still appropriate to check your hormone levels and ovulation if you are having trouble conceiving.

RELATED: Period Tracking for Female Athletes

Vaamonde also suggests that female athletes pay close attention to their overall health and wellbeing, since the female athlete triad of energy deficiency, amenorrhea (absent or irregular periods), and osteoporosis is a concern. These factors may impact your ability to conceive, but has health implications well beyond any potential pregnancy, too.

Fertility in females is not only a matter of energy availability— here’s a brain component, too. According to a 2012 study by researchers at Boston University School of Public Health, highly vigorous exercise, done on the regular, can disrupt the information received by the corpus luteum (the part of the follicle that remains after ovulation). Since the corpus luteum produces progesterone, which is necessary for pregnancy, that can thwart your efforts.

And that’s not all. A 2022 study on female endurance athletes found that, when compared to non-athletic women, they had higher levels of androgens and corticosteroids—both of which can negatively impact the ability to conceive.

But, real talk. If you’re having trouble getting pregnant, how likely is it, really, that your exercise habits are to blame?

Around 10% of women deal with some sort of infertility, and their risk increases with age. But, while low body fat due to excessive exercise and being underweight are listed as common causes of female infertility by the Cleveland Clinic, they’re far from the only common causes. After all, plenty of lean, active women conceive without any trouble.

Researchers at the Norwegian University of Science and Technology looked into differences in fertility between women who trained almost every day and women who trained until exhaustion, based on information initially gathered about their physical activity and follow-up data on pregnancy and childbirth gathered a decade later. They found that 11% of the near-daily exercisers reported fertility problems, and a whopping 24% of those who exercised to near exhaustion did as well. That relationship between exercise and fertility was even clearer with women under 30, since age is so closely tied to fertility in women.

And the age factor is particularly noteworthy here, since women enjoying success in their athletic prime may also be more likely to put off starting a family until later in their triathlon career, and since female fertility decreases significantly by the age of 35 (and even more so at 40) a person’s trouble conceiving may be tied to age, not activity.

Photo: Getty Images

What you can do to increase the odds of conception

All of this might sound intimidating, but don’t put your bike out to pasture just yet. There are things you can do to up your chances without hanging up your kit.

But first, you need to take stock of where you land in the realm of triathlon training. Vaamonde said that it’s important to distinguish between leisure, amateur, and professional athletes. There are likely to be significant differences between their training loads and lifestyles, and those differences, as we’ve now seen, can affect fertility in men. A 2012 Boston University study found this to be generally true for women, too; lean women who reduced their exercise from vigorous to moderate improved their fertility. However, for overweight or obese women, the findings suggested that any type of physical activity, even if it was vigorous, could be beneficial to their fertility.

So, what does that really mean?

“To reduce the risk of infertility/subfertility, keeping training load at a healthy level would be a must,” Vaamonde said. A “healthy level” is different from one athlete to the next, but in general, your training should be in balance with your recovery. Many of the symptoms of overtraining, the Female Athlete Triad/Male Athlete Triad, and low energy availability overlap to indicate an imbalance between training and recovery, and training should be scaled back. These symptoms include:

  • Trouble sleeping
  • Reduced sex drive
  • Lack of appetite
  • Mood changes
  • Decreased motivation
  • Frequent injuries

Of course, when it comes to professional athletes, she acknowledges that this may not always be an option. After all, training to win is their job, and it’s one thing for a female pro to scale back while pregnant and postpartum, but doing so prior to conception may be a hard sell.

Still, there are important steps athletes can take. “I would recommend that if fertility is their concern, they contact a fertility specialist and check their fertility,” she said. Getting a baseline on your fertility and continuing to check it with a professional is important, according to Vaamonde, because many athletes begin training at a young age — often, in prepubescent years — and that can make it hard to see the connection between exercise and any reproductive disturbances. “Performing regular reproductive checks may help the person assess their reproductive potential and whether or not this is being altered, so early screening is paramount,” Vaamonde said. When it comes to testing your fertility, there are a variety of options. Women can get their anti-Mullerian hormone (AMH) levels tested at their doctor’s office, lab, or with an at-home kit, while blood tests can measure levels of follicle-stimulating hormone (FSH). Other tests, ranging from blood and urine tests, x-rays of the uterus and fallopian tubes, and, for men, a semen sample, may also be recommended, but talking to your doctor about your concerns and asking about available tests is always a great place to begin. He or she may then refer you to other specialists if needed.

Whether you’re a professional, a newbie, or somewhere in between, Vaamonde believes having energy availability that matches energy expenditure may be an appropriate strategy, especially for female athletes who are experiencing irregular or absent cycles.

RELATED: The Right Way to Calculate Calories Burned in Training

And supplements could be an option in some cases, she said. “Oxidative stress, aka the imbalance between free radicals, and most importantly reactive oxygen species, and antioxidants, can be suspected. Therefore proper antioxidant supplementation may also help,” Vaamonde said. Compounds like vitamin C, resveratrol, N-acetylscysteine, and Coenzyme Q10 are good examples. But that can be an issue for professionals, as she notes some compounds may interfere with performance or show up in a doping screening; both the compound and the dosage can be a factor here.

Steps to take

The bottom line is, if you’re concerned about your fertility, there are a few steps you can take to boost your odds of making a baby:

It’s also important to note that you don’t have to figure this out yourself. Said Vaamonde: “These assessments require a good understanding and working between professionals, ideally in multidisciplinary teams—sport coaches, nutritionists, OB GYN physicians, and andrologists.”