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“Saving Swimmers” - the effects of training, mechanical stress and
performance-enhancing drugs on male fertility
Dr Jon Patricios, Sports Physician
The last 2 decades have seen significant changes in exercising patterns amongst
both professional and recreational athletes. Endurance running and mass cycling
events, many of them multi-stage, have increased in popularity whilst triathlon
has become one of the fastest-growing sports.
As much as these levels of
exercise participation may be viewed as positive, negative trends have also
emerged including an increasing use of anabolic steroids especially in
recreational athletes, many of them young. Over the same period there has been
an increasing incidence of infertility (described as the inability to achieve a
successful pregnancy after 12 months of regular unprotected intercourse). Is
there a link between exercise trends and male infertility and should men be
more proactive to improve their chances of producing offspring?
Intense exercise – stifling sperm
Exercise is accepted as being healthy for all aspects of our physical and mental
wellbeing. Testicular function is no exception. Animal and human models have
demonstrated slower rates of age-related decline in testicular function reflected
by higher levels of circulating testosterone, higher concentration of sperm in
semen and better sperm motility than in non-exercised animals. However,
intense exercise may have more deleterious effects on semen and fertility. There
is growing evidence and concern that exercise, when excessively practiced, may
lead to adverse effects on the reproductive system and fertility. This occurs when
exercise, itself a stress on the body, is increased in duration and or intensity and
challenges the body’s ability to maintain homeostasis (its sense of physiological
There appears to be a volume threshold for the effect of training on sperm
parameters and hormones. In other words, the beneficial effects of exercise on
the male reproductive system are only produced to a certain intensity of
exercise. Such a threshold has been observed both in running and in cycling.
Running dry and pedaling poor
High mileage runners (greater than 95km/week) have been found to have far
poorer parameters of sperm health including sperm that are lower in number,
more abnormal-looking, less motile and less effective at penetrating mucus, and
a volume of 300km/week in cycling correlates with potential fertility
impairment from a sperm morphology point of view
When endurance-trained and resistance-trained athletes were compared with
sedentary controls, sperm density, motility, morphology and sperm penetration
of standard cervical mucus were significantly altered only in the endurancetrained runners. Training volume (expressed as km/week), was significantly
correlated to sperm motility and density.
In another study, in which 286 exercising subjects were divided into moderateintensity exercise (60% of VO2max) and high-intensity exercise (80% of
VO2max) groups, midway through the running- phase the subjects in the highintensity exercise group showed a significant decline in semen parameters
compared to those athletes exercising at moderate intensity. The changes
reversed during recovery but the researchers correctly point out that the
deleterious effects may not be reversible if athletes have been training for longer
periods of time (years) or had started training around puberty.
It is important to place these findings in perspective. Almost all studies have
found that changes tend to be temporary, correcting within days to weeks.
Moreover, even a below-average sperm count doesn’t necessarily make that
individual infertile. However, little information is available on athletes who
regularly engage in high mileage training week in and week out. This may be a
group at higher risk of chronic low sperm count and abnormal morphology.
Cycling – sacrificing swimmers
Professional cyclists have been shown to consistently have higher testosterone
levels than most sportsmen. However, their sperm motility and morphology
(shape) appears to be worse than average especially during competition.
Postulated reasons include the increased testicular temperatures and the
psychological stress associated with competition. One function of the scrotum is
to keep the testes outside of the body and at a lower temperature to the core.
Testicular temperature must be maintained at approximately 2.5°C below core
body temperature for normal spermatogenesis. The regulatory role of the
scrotum in sustaining this lowered testicular temperature is achieved through
the combined function of the cremasteric and dartos muscles (by moving the
testicles closer or further away from the body) as well as the venous plexus of
the spermatic cord (acting as a counter-current heat exchanger). Cycling
counters this with tight-fitting shorts and a saddle that compress the testes close
to the body. In other forms of exercise vascular shunting away from the scrotum
combined with increased air circulation around the scrotum actually decreases
scrotal temperature during exercise.
A study on mountain bikers found 96% to have scrotal abnormalities as
compared to 48% of road cyclists and 16% of controls. Testicular calcifications,
hydroceles (small, fluid-filled sacks) and varicoceles (enlarged, twisted scrotal
veins) were all more common. All these abnormalities could affect reproductive
health. Again, this does not necessarily correlate with infertility but is a
reflection of the potential effects of repetitive microtrauma.
In summary, as with most areas of human physiology, testicular health is
enhanced by regular low to moderate intensity exercise but there is evidence
from both animal and human studies that suggests that long-duration and
intense exercise may compromise hormonal status and adversely affect sperm
production and morphology. Cycling in particular, because of raised testicular
temperatures and repetitive microtrauma, may predispose to poor sperm health.
Adapted from Du Plessis S et al. Is There a Link between Exercise and Male
Factor Infertility? The Open Reproductive Science Journal, 2011, 3, 105-113
Destructive doping
Testosterone was first isolated as a substance in 1935 and, since then, the use of
testosterone-derived anabolic androgenic steroids (“steroids”) has been
described in body builders and sports cheats for decades, starting with Russian
weightlifters in the 1950’s. However, the use of steroids has extended to
recreational athletes and even schoolchildren. In the USA steroid use is
estimated to be 3 million with two thirds being recreational users principally for
aesthetic purposes. Moreover, commercially available supplements have a
steroid contamination rate of 15-20%. Exposure to these drugs at a young age
may result in them having significant effects on a developing body and longer
use may result in an exponential increase in side effects.
One of these effects is infertility. Up to 50% of cases of infertility are accounted
for by the male. The “underground” culture of steroid use and abuse results in
little interaction between users and medical professionals often until infertility is
eventually diagnosed.
There is a considerable body of scientific evidence that the use of steroids
negatively affects male fertility. The effects of the testosterone-derived steroids
results in testicular atrophy (shrinking testes), oligospermia (fewer sperm) and
azoospermia (deformed sperm). Simply put, using anabolic steroids not only
reduces the number of sperm but affects their quality.
These effects result from a dampening effect that steroids have on the areas of
the brain that regulate hormone production as well as a direct toxic effect on the
testes. Therefore, somewhat ironically, although blood levels of testosteronederived steroids are high, the small, inefficient testes produce fewer healthy
sperm. In one study, sperm counts fell by 73% and in three individuals
azoospermia (complete absence of sperm) was present when high doses of
anabolic steroids were taken chronically. Even in those individuals with sperms
present, there was a 10% increase in the number of immotile sperm and a 30%
decrease in the number of motile sperms. Thus, fertility was severely reduced in
males, which provides confirmation of many clinical reports of the same
phenomena. In another study conducted on bodybuilders in Parma, Italy, the two
most enduring effects of 2 years of steroid use were elevated cholesterol and
reduced altered sperm count and morphology resulting in a lower fertility index.
In addition, low levels of the body’s own (endogenous) testosterone result in low
libido and erectile dysfunction further diminishing the prospects for
Abnormalities in sperm parameters may correct in 4-12 months but much longer
effects have been documented particularly where high doses, multiple steroids
(“stacking”) and long-duration use have taken place. There are documented
cases of the testosterone-producing Leydig cells, never recovering.
Treatment of steroid-induced infertility takes several forms. A passive approach
is to wait for correction of the hormonal status and for normal sperm production
to resume. This may take months to years. A more proactive intervention
involves stimulation with a group of drugs known as gonadotropin analogues
including human chorionic gonadotropin (hCG), recombinant menopausal
gonadotropin (rMG) and follicular stimulating hormone (FSH). Some steroid
users are now proactively using hCG as part of their drug regimen especially
after a steroids cycle to try and mitigate the effects of steroids on sperm. Cases of
sperm correction have been noted but most often the sperm abnormal in
morphology and hypomobile (“slow”). In other words, using hCG concomitantly
with steroids may help to maintain sperm count but the quality of sperm
remains poor. The steroid abuser is still left with “bad swimmers”.
Differing patterns in steroid use, types of drug, doses, regimens as well as
individual tolerance of these drugs makes predicting their effects very difficult.
There is, however, a substantial enough body of evidence to illustrate the
deleterious effects that anabolic steroid use has on male fertility. Sporting and
recreational users who wish to have children should consider pro-active steps
including regular monitoring by a urologist and fertility clinic and preserving
sperm before embarking on the use of such drugs.
A Solution – “Saving the swimmers”
The sporting public, many of whom are in their reproductive years, should be
aware that high intensity exercise may have an effect on sperm count and quality
through systemic hormonal changes, local unfavourable temperatures and
microtrauma. High load training and steroid use should form part of any
modern-day medical history.
The fertility consequences of both training and steroid use may be short or
longer-term and vary between individuals. Banking sperm whilst still healthy
has been used proactively by men for many reasons including before undergoing
cancer treatments, prostate surgery or vasectomy and also for those entering
high-risk occupations which expose them to extremes of heat, radiation and
chemicals. With Netcells Biosciences he cost is under R5 000 which includes a
year’s storage but sperm may be stored indefinitely for a small annual storage
fee. Once needed, insemination can take place at any fertility clinic of your
choice. This knowledge, together with an appreciation of the much greater
financial and emotional costs of infertility treatment, make self-donation and
preservation of sperm in a sperm bank appear to be a logical and cost-effective
means of preserving reproductive potential. “Saving swimmers” may yet salvage
a sportsman’s seed.