Exercise. Fitness. Health. Wellness. Sex. Now do I have your attention?
But, now that I have your attention, and if you’re a teenage male, you might be “at attention” but calm yourself down. This article isn’t about positions, tantric techniques, or some cosmopolitan magazine write-up. This article is about how men’s sex lives are being impacted by exercise or lack thereof. The only position you’ll need for this is “chair position” meaning, sit back, relax, and read. Then when you’re done reading, go exercise so you get the benefits for those other positions later.
Let’s start with something that will continue to keep your attention: Research indicates men’s fitness levels significantly improve the perception of sexual performance and sexual desirability.  Meaning, if a male exercises, he tends to believe that he’s better between the sheets and he is more attractive to a mate. Usually we hear about the benefits of exercise in regard to weight management, cholesterol, diabetes, cardiovascular diseases, chronic diseases, etc. How about this for a change up: Exercise improves your sex life, or at least the perception of it.
But wait, there’s more: another study found that objective measures of the quality of women’s sexual partners such as: men’s attractiveness and masculinity rated based on facial images, significantly predicted women’s orgasms.  How about that for a “Whoa!” moment. Didn’t I tell you there was more?
The Sire Choice Hypothesis, which describes the evolutionary benefits of a woman’s orgasm being related to an increase in probability of fertilization from high quality male partners. The mechanisms of action for the Sire Choice Hypothesis are based on evidence that orgasm in a woman serves as a mysterious post intercourse choice potentially based on a surge of the hormone oxytocin, released during female orgasm which facilitates uterine contractions responsible for sperm transportation to the reproductive tract. If this signal is correct, female orgasm would increase the likelihood of conception.  In other words, women tend to orgasm more frequently when having intercourse with an attractive, masculine male who fits certain criteria (see below) and one byproduct of orgasm is increased oxytocin which causes uterine contractions. The uterine contractions then lead to an increase in the likelihood that sperm will travel to the reproductive tract where conception can occur.
Briefly before moving on, I wanted to spend a quick minute defining “masculine” based on the two studies previously cited. In the first study cited , masculine was defined strictly based on facial imaging where women used a seven point scale: 1=very feminine, 7=very masculine. In the second study referenced  orgasm intensity and frequency were related to having a partner that was expressive and nurturing, giving of time (intensity only, not frequency), sexually proceptive, monetarily investing, and physically protective. These qualities were assessed by the Partner Specific Investment Inventory which is a 62 item questionnaire using a 5 point Likert scale with potential responses ranging from “Strongly Disagree” to “Strongly Agree”. In case you want to cover your bases, below are examples of the questions for each of the significantly related categories.
- Expressive/Nurturing – “He/she shares his/her feelings with me”
- Tolerant/Permissive/Agreeable – “He/she doesn’t become jealous when I spend my time with other people”
- Future-Oriented – “When he/she talks about the future, I’m always in it.”
- Giving of Time – “He/she spends a lot of time with me.”
- Sexually Proceptive – “He/she wants to have sex with me.”
- Monetarily Investing – “He/she pays for our evening entertainment”
- Honest – “He/she tries to deceive me”
- Physically Protective – “He/she makes sure I don’t have to go out alone at night”
- Socially Attentive – “He/she deserts me at parties”
- Good Relationship with Partner’s Family – “He/she enjoys my family gathers”
- Not Sexualizing of Others – “He/she talks about the attractiveness of other women/men in my presence”
|Variable||Orgasm intensity||Orgasm frequency||Fake orgasm frequency|
|Giving of Time||.26**||.15||-.11|
|Good Relationship with Partner’s Familya||.06||.01||.01|
|Not Sexualizing of Othersa||.06||-.04||.05|
Ellsworth, R. M., & Bailey, D. H. (2013). Human female orgasm as evolved signal: A test of two hypotheses. Archives of Sexual Behavior, 42(8), 1545-1554.
So far so good. But it’s not all sunshine and rainbows because there’s a few problems.
With age, it is natural to lose testosterone as a man. I’m sure you’ve seen or at least heard of hormone replacement therapy through commercials or otherwise, as it’s become quite a popular treatment. For men, testosterone is a key hormone. Low-serum testosterone has been associated with many age-related adverse health conditions including abdominal obesity, diabetes and prediabetic states, dyslipidemia, low bone and muscle mass, depressed mood, decreased quality of life, and finally, impaired sexual function. 
A study published in 2007 by Travison et al., measured the magnitude of change at a population level in serum testosterone concentrations and to what degree these changes are explained by lifestyle factors such as body weight. The study observed men of a similar age at three different time points. See chart below for details.
|Study Wave||Observation years||Age range(yr)||n||**TT (ng/dl)
|**Bioavailable T (ng/dl)
|**Bioavailable T (ng/dl)
Travison, T. G., Morley, J. E., Araujo, A. B., O’Donnell, A. B., & McKinlay, J. B. (2006). The relationship between libido and testosterone levels in aging men. The Journal of Clinical Endocrinology & Metabolism, 91(7), 2509-2513.
As you can see from the chart, testosterone bioavailability lessens over time and according to the authors, there appears to be no clear reason why. The authors note that although there were noticeable increases in the proportion of subjects who were overweight or obese, it did not appear to explain the observed age-matched trends in testosterone.
However, other research may help to give a clearer picture. A study  examining 70 men between the ages of 20 and 62 years of age found obese men had a significantly lower testosterone concentration than other groups and showed a negative correlation with BMI, waist circumference, and insulin levels.
Osuna C, J. A., Gomez-Perez, R., Arata-Bellabarba, G., & Villaroel, V. (2006). Relationship between BMI, total testosterone, sex hormone-binding-globulin, leptin, insulin and insulin resistance in obese men. Archives of andrology, 52(5), 355-361.
In men, there appears to be an association between testosterone and libido. As testosterone increases, libido increases; as testosterone decreases, libido decreases.  And as previously noted, testosterone tends to impact mood, quality of life and sexual function.
So, what can you or someone you know do to increase testosterone and get that libido going again to change your sex life for the better?
If you’re like most guys who go to the gym, you might think lifting weights would increase testosterone more so than other forms of exercise. Maybe, but the act of weight lifting might not be the sole reason why. While there is a short-term endocrine response which increases free and total testosterone immediately following a post workout pump, testosterone levels return to baseline within about 30 minutes. And long-term strength training does not appear to change resting total and free testosterone concentrations in response to high or moderate volume. 
However, moderate exercise of any form might do just what you’re looking for. A study  of over 500 members of the Fifty Plus Fitness Association, an organization of older persons who are bonded by the pursuit of a physically active lifestyle, found that fitness levels are positively associated with frequency of sexual intimacy. 46%, 60%, and 63% of males reported one or more bouts of sexual intimacy per week for the least, middle, and most fit groups, respectively. Improved fitness also showed a strong positive correlation with the level of satisfaction in men. The activities performed in this study were wide ranging but most commonly included jogging, biking, and walking.
But be careful, there is strong evidence that there is an endurance exercise volume threshold, which when surpassed can take you from increased sexual intimacy and function to reducing sexual function and all things male fertility. A study by Vaamonde et al. showed that a cycling volume of 300km/week correlates with serious fertility impairment in the form of sperm morphology and may lead to serious impairment of male fertility. 
Another study by De Souza and co-workers reported that high mileage runners, approximately 110 km/week (68 miles/week), had significantly lower levels of total testosterone and free testosterone compared to moderate-mileage runners (approximately 54 km/week) and sedentary control groups of a similar age. In addition, sperm concentration and total number of motile sperm were significantly lower in high-mileage runners compared to sedentary controls. 
And finally, Safarinejad et. al. randomly assigned 286 subjects to two exercise groups: moderate intensity exercise (60% of VO2max) and high intensity (80% of VO2max). Both groups exercised for 60 weeks performing treadmill running for 120 minutes, 5 sessions per week followed by a 36-week low intensity recovery period. The authors note that starting in week 12 onward, serum and free testosterone began to decrease and subjects in the high intensity exercise group showed a significant decline in semen parameters compared to subjects in the moderate intensity group. But important to note, is that all of the parameters returned to their pre-exercise levels during the recovery period. 
When it comes to exercise, remember to “stimulate, not annihilate”. Tiredness and fatigue from surpassing a volume threshold of exercise and intensity may result in reduced sexual desire, libido, and even the ability to get an erection. 
And as far as testosterone and nutrition goes, there appears to be a few things to be cautious about, especially if you practice any sort of food restrictions. Let’s take a look at a couple examples:
A case study of a 19-year-old male with a history of type 1 diabetes reported complete loss of libido and erectile dysfunction that had begun 12 months prior. The male was reported to previously be in good health and was sexually active with sufficient libido. There was no history of androgen abuse or any hormonal medication and had a BMI of 22. On the first assessment, he showed low free and total testosterone. A normal range of free testosterone is between 50-210 pg/mL and total testosterone between 260-1000 ng/DL, while this subject presented a free testosterone level of 35.5 pg/mL and total testosterone level of 339 ng/dL. The cause appeared to be nutrition related, stating that he recently started a vegan diet consuming a large amount of soy products equaling 360 mg of isoflavones per day over the course of one year. To put this in perspective, the average dietary isoflavone intake in Western countries is as low as 2 mg/day. Upon the cessation of the vegan diet, the subject returned to normal ranges of free and total testosterone. 
Siepmann, T., Roofeh, J., Kiefer, F. W., & Edelson, D. G. (2011). Hypogonadism and erectile dysfunction associated with soy product consumption. Nutrition, 27(7-8), 859-862.
Interesting enough, poorly planned vegetarian diets are commonly found to be low in zinc.  Zinc is primarily found in meat, fish, and poultry in the adult omnivorous diet, however vegetarians typically obtain zinc from foods such as cereal, grains, legumes, nuts, and seeds. The problem is that their bioavailability is much poorer when obtained from plant-derived foods compared to animal foods. This may require strict vegetarians to consume as much as 50% more zinc than individuals consuming an omnivorous diet. In fact, a recent meta-analysis found that vegetarians were overall found to have lower dietary zinc intakes and serum zinc concentrations compared to their nonvegetarian control groups. 
So why am I talking about vegetarians and zinc? Well, without careful nutritional planning, vegetarians, like our case study example, may present low zinc status which has been shown to have a negative impact on testosterone. 
In a cross-sectional study of forty men between the ages of 20 and 80 years old, researchers set out to measure the relationship between cellular zinc and serum testosterone. To do this, subjects received a diet of, you guessed it, soy products such as soy chicken and soy hamburgers to induce a zinc deficiency. The diet supplied all other essential nutrients according to the RDA except zinc. This resulted in a significant decrease in serum testosterone concentrations after 20 weeks of zinc restriction. Additionally, the study examined the effects of zinc supplementation of marginally zinc-deficient elderly men for six months which resulted in nearly doubling the serum testosterone levels from 8.3 + 6.3 nmol/L to 16.0 + 4.4 nmol/L. 
A zinc deficient diet is not the only example of nutrition playing a role in low testosterone levels. A case study  examined a 22-year-old man with lack of libido and erectile dysfunction. The subject engaged in regular bodybuilding exercises and had an excellent medical history, however, an analysis of his diet revealed the subject was eating less than 20 grams of fat per day. After a three month trial of increasing his fat intake to 30% of total calories, the subject went from a bioavailable testosterone level of 0.16 ng/mL to 1.02 ng/mL. In addition, his libido and ED was resolved.
Other research will back up this case study. A study  performed in Eastern Finland studied 30 healthy, non-obese men between the ages of 40-49 years old to determine what effect dietary fat had on serum sex hormones in men. The study had three phases, baseline or the subjects’ normal current diet, an intervention protocol, and a return to the baseline diet. The baseline diet was tracked for two weeks, the intervention protocol was performed for six weeks, and then a transfer back to normal diet for six weeks. During the intervention protocol, there was a reduction in dietary fat which was replaced by low fat options, however, the researchers attempted to keep the diets isocaloric and estimate they did so within 5%. During the low-fat intervention period, the daily fat intake was reduced from a mean of 147g fat/day to 76g fat/day or a reduction of approximately 40% of total energy intake to 25%. The data show a change in dietary fat resulted in a mean decrease of 15% in serum testosterone concentrations.
Viagra and Cialis. We’ve heard their commercials approximately one billion times, so clearly there’s a high demand for these pharmaceuticals, potentially due to the quantitatively lower testosterone a man exhibits now than in the past. ED is defined as the inability to attain and maintain an erection sufficient to permit satisfactory sexual performance.  I guess just like “beauty is in the eye of the beholder”, “satisfactory” is also a subjective quality—so you (and your partner) be the judge if ED is affecting you or not. Even if it’s not affecting you, did you know: erectile dysfunction (ED) affects more than half of all men between the ages of 40 and 70 years old? 
Let me give you another, “did you know?” Did you know: Many studies have shown that ED shares several modifiable risk factors with cardiovascular disease such as atherosclerosis, hypertension, hyperlipidemia, diabetes mellitus, smoking, obesity, and sedentary lifestyle.  Data from studies examining patients with cardiovascular disease have shown a high prevalence (42% to 75%) of ED.  In fact, men with hypertension have a 15% chance of developing full-onset ED and that number increases to 20% if they smoke. 
Really when you think about the physiology of an erection, it makes sense that hypertension and smoking increase the odds of developing ED. Erections are nothing more than filling a chamber with blood. Arousal increases blood flow to the penis and the penis becomes erect. When arousal ceases, blood leaves the penis and the penis becomes flaccid. It’s all about the ability for blood to flow freely. By definition, atherosclerosis is a hardening or loss of elasticity of arteries making it more difficult for blood to flow.  Atherosclerosis can be caused by hypertension, hyperlipidemia, diabetes mellitus, smoking, obesity, and sedentary lifestyle.  Sound familiar?
But there’s hope. Several recent studies all come to similar conclusions: physical activities levels seem to predict the prevalence and incidence of ED.  Lifestyle changes such as weight loss and physical activity are effective methods in modifying ED in moderately obese and sedentary men. 
For instance, men with a body mass index (BMI) greater than 28.7 have a 30% higher risk for erectile dysfunction than those with a normal BMI (18.9-24.9).  In fact, as high as 79% of men who are considered overweight or obese by BMI standards report symptoms of erectile dysfunction, however vascular factors related to increased body weight may also play an important role in that number.  With that said, obesity is an independent risk factor for cardiovascular disease and is associated with low-grade inflammation which is associated with endothelial dysfunction.  The endothelium are the cells that line the inner walls of blood vessels and helps to control the elastic qualities of the vessels. Erectile dysfunction and endothelial functions may actually share some similar pathways through a defect in nitric oxide activity. For all the lifters out there, we know nitric oxide is a vasodilator used in many supplements to increase blood flow.
Lucky for us, there is a study that tested this exact hypothesis. A study by Esposito et al., 2004, performed a study on 110 obese men aged 35-55 years of age with erectile dysfunction to determine if lifestyle changes designed to obtain and sustain long-term weight reduction and an increase in physical activity positively impacted erectile and endothelial functions. Men were randomly assigned to either an intervention group or a control group. Men in the intervention group were given detailed advice about how to achieve weight loss such as caloric intake requirements, goal setting advice, and tracking food via food diaries. The intervention group also received guidance on increasing physical activity level. Men in the control group were given no specific information about diet or exercise. After two years in the program, men in the intervention group had significant decreases in body weight and BMI, blood pressure, glucose levels, insulin, total cholesterol and triglycerides, and a significant increase in HDL cholesterol while the control group had no significant changes. To top it off, erectile function score, which was measured via the International Index of Erectile Function questionnaire, improved in the intervention group while the control group experienced no changes. The researchers noted that 31% of the men in the intervention group regained sexual functioning and 68% of the variability in score changes were completely explained by the changes in BMI, physical activity, and C-reactive protein (CRP) levels, which is a marker of inflammation. The researchers also noted that endothelial function and markers of systemic vascular inflammation were associated with this improvement. 
This is great news. The data from this study clearly demonstrates that lifestyle changes such as healthy dietary habits, caloric reduction, and increased physical activity improve erectile function in obese men and resulted in one-third of men with ED regaining sexual functioning. Instead of needing to take a little blue pill every time you want to get a little hot and heavy, exercise can make you long and strong to help you get your groove on.
Esposito, K., Giugliano, F., Di Palo, C., Giugliano, G., Marfella, R., D’andrea, F., … & Giugliano, D. (2004). Effect of lifestyle changes on erectile dysfunction in obese men: a randomized controlled trial. Jama, 291(24), 2978-2984.
This is not the only study that demonstrates the benefits of physical activity on ED. In one of the largest studies on erectile dysfunction and modifiable risk factors, which surveyed 31,742 male health professionals with no known history of prostate cancer ranging in ages from 53-90 years old at the time of the survey found: 
- Men with a healthy lifestyle and no chronic disease had the lowest risk for erectile dysfunction at all ages.
- In men younger than 60 years of age who had at least one comorbid condition, the prevalence of erectile dysfunction was double that of healthy men. Comorbid conditions most strongly associated with ED excluding prostate cancer were diabetes, non-prostate cancer, and stroke. Use of beta-blockers and antidepressant medication were also significantly associated with ED.
- There was an inverse relationship between physical activity and erectile dysfunction. Frequent vigorous activity was associated with a 30% reduction in risk for erectile dysfunction compared to very little or no exercise. The authors note that younger men (<60 years old) benefited more from exercise than older men (>80 years old).
- Moderate alcohol consumption and refraining from smoking had inverse relationships with ED.
- Being overweight, watching more than 20 hours of television per week, smoking, were strongly associated with increased risk for ED in younger men.
|Increases Risk for ED||Decrease Risk for ED|
|Have at least one co-morbid condition such as diabetes, non-prostate cancer, stroke||Free of comorbid conditions|
|Very little or not physical activity per week (less than 2.7 MET hours per week)||Vigorous physical activity at least 32.6 MET hours per week (equivalent to 3 hours of running)|
|Use of beta-blockers or antidepressants||BMI: Normal|
|BMI: Overweight and/or Obese||Moderate alcohol consumption and not smoking|
|Watch >20 hours of TV per week|
Figure: Reported prevalence of erectile dysfunction in the previous 3 months according to disease status and lifestyle risk factors.
*Chronic disease includes other cancer, heart disease, hypertension, diabetes, or stroke. †Risk factors include antidepressant use, consumption of more than two alcoholic drinks per day, smoking, body mass index 25 kg/m2, exercise 21.5 metabolic equivalents per week, or television viewing 8.5 h/wk
Bacon, C. G., Mittleman, M. A., Kawachi, I., Giovannucci, E., Glasser, D. B., & Rimm, E. B. (2003). Sexual function in men older than 50 years of age: results from the health professionals follow-up study. Annals of internal medicine, 139(3), 161-168.
Not only can watching too much TV increase your chances of acquiring ED, it may also reduce the semen quality in young men. One study  measured 222 men with a median age of 19.6 years old, over half of which had a normal BMI, and over ¾ were non-smokers. The men were asked to report the number of hours watching tv as well as exercise in a mild, moderate, or vigorous fashion over the past three months. Researchers collected semen samples via masturbation after being asked to abstain from ejaculation for at least 48 hours prior to the sample collection. Results of the study show that moderate to vigorous physical activity was positively related to sperm concentration with men in the highest quartile of physical activity producing a 73% higher sperm concentration compared to the lowest quartile. Light physical activity did not produce superior levels of sperm concentrations. TV watching was inversely related to sperm concentrations. Men in the highest quartile of TV watching had a 44% lower sperm concentration than men in the lowest quartile of TV watching.
What if you watched a lot of TV and didn’t exercise at a moderate to vigorous level? You guessed it. Those subjects did the worst. Men with the highest TV watching (>14 hours/week) and lowest physical activity levels (0-4.5 hours/week) had the lowest adjusted mean sperm concentration.
Gaskins, A. J., Mendiola, J., Afeiche, M., Jørgensen, N., Swan, S. H., & Chavarro, J. E. (2015). Physical activity and television watching in relation to semen quality in young men. Br J Sports Med, 49(4), 265-270.
In another study examining over 26,000 couples planned pregnancies found that infertility was significantly related to men’s BMI.  This information may be helpful considering approximately 9% of men and 11% of women of reproductive age in the US have experienced fertility problems and 12-15% of couples are unable to conceive after one year of having unprotected sex. 
Recap of Key Points
- Research indicates men’s fitness levels significantly improve the perception of sexual performance and sexual desirability 
- For men, testosterone is a key hormone. Low-serum testosterone has been associated with many age-related adverse health conditions including abdominal obesity, diabetes and prediabetic states, dyslipidemia, low bone and muscle mass, depressed mood, decreased quality of life, and impaired sexual function.  Unfortunately, the bioavailability testosterone has been significantly reduced over time.
- Obese men tend to have a significantly lower testosterone concentration than other groups and showed a negative correlation with BMI, waist circumference, and insulin levels.
- Moderate exercise has been shown to increase the number of bouts of sexual intimacy per week and improved fitness also showed a strong positive correlation with the level of satisfaction in men. 
- There is strong evidence that there is an endurance exercise volume threshold, which when surpassed can take you from increased sexual intimacy and function to reducing sexual function and all things male fertility.   
- Poorly planned diets have potential to cause negative effects on the male sex life.     
- Erectile dysfunction (ED) affects more than half of all men between the ages of 40 and 70 years old? 
- Having cardiovascular disease, hypertension, and smoking all increase the risk of erectile dysfunction however, physical activities levels seem to predict the prevalence and incidence of ED. Lifestyle changes such as weight loss and physical activity are effective methods in modifying ED in moderately obese and sedentary men. 
- Men with the highest TV watching (>14 hours/week) and lowest physical activity levels (0-4.5 hours/week) had the lowest adjusted mean sperm concentration. 
When I started writing this article, I thought it might be a fun and light-hearted topic about how exercise frequency led to having more sex and more satisfying sex. Little did I know, I opened a can of worms that took me all over the place searching for more and more research. Every time I read research and wrote about it, I had more questions and more topics to look up. As someone who has taught sexual education at the high school level and has been trained to do so through college degrees in health and physical education and exercise science and health promotion, I am shocked at the lack of time these topics are given and discussed given what I know now. For most of us, sexual functioning and health is a huge factor in a satisfying life, and I cannot imagine the frustration it must cause those who experience it. I hope that this article sheds light on a few reasons why someone might be experiencing lack of sexual functioning and give ideas to investigate the cause. The more I learn, the more it appears true no other activity I’ve come across can even come close to the impact that exercise and nutrition have on the entire human body and all of its workings.
- Penhollow, T. M., & Young, M. (2004). Sexual desirability and sexual performance: does exercise and fitness really matter?. Electronic Journal of Human Sexuality, 7.
- Puts, D. A., Welling, L. L., Burriss, R. P., & Dawood, K. (2012). Men’s masculinity and attractiveness predict their female partners’ reported orgasm frequency and timing. Evolution and Human Behavior, 33(1), 1-9.
- Ellsworth, R. M., & Bailey, D. H. (2013). Human female orgasm as evolved signal: A test of two hypotheses. Archives of Sexual Behavior, 42(8), 1545-1554.
- Travison, T. G., Araujo, A. B., O’donnell, A. B., Kupelian, V., & McKinlay, J. B. (2007). A population-level decline in serum testosterone levels in American men. The Journal of Clinical Endocrinology & Metabolism, 92(1), 196-202.
- Osuna C, J. A., Gomez-Perez, R., Arata-Bellabarba, G., & Villaroel, V. (2006). Relationship between BMI, total testosterone, sex hormone-binding-globulin, leptin, insulin and insulin resistance in obese men. Archives of andrology, 52(5), 355-361.
- Travison, T. G., Morley, J. E., Araujo, A. B., O’Donnell, A. B., & McKinlay, J. B. (2006). The relationship between libido and testosterone levels in aging men. The Journal of Clinical Endocrinology & Metabolism, 91(7), 2509-2513.
- Vingren, J. L., Kraemer, W. J., Ratamess, N. A., Anderson, J. M., Volek, J. S., & Maresh, C. M. (2010). Testosterone physiology in resistance exercise and training. Sports medicine, 40(12), 1037-1053.
- Bortz 2nd, W. M., & Wallace, D. H. (1999). Physical fitness, aging, and sexuality. Western Journal of Medicine, 170(3), 167.
- Vaamonde, D., Da Silva-Grigoletto, M. E., García-Manso, J. M., Cunha-Filho, J. S., & Vaamonde-Lemos, R. (2009). Sperm morphology normalcy is inversely correlated to cycling kilometers in elite triathletes. Revista Andaluza de Medicina del Deporte, 2(2).
- De Souza, M. J., Arce, J. C., Pescatello, L. S., Scherzer, H. S., & Luciano, A. A. (1994). Gonadal hormones and semen quality in male runners. International journal of sports medicine, 15(07), 383-391.
- Safarinejad, M. R., Azma, K., & Kolahi, A. A. (2009). The effects of intensive, long-term treadmill running on reproductive hormones, hypothalamus–pituitary–testis axis, and semen quality: a randomized controlled study. Journal of Endocrinology, 200(3), 259-271.
- Du Plessis, S. S., Kashou, A., Vaamonde, D., & Agarwal, A. (2011). Is there a link between exercise and male factor infertility. Open Reprod Sci J, 3, 105-13.
- Siepmann, T., Roofeh, J., Kiefer, F. W., & Edelson, D. G. (2011). Hypogonadism and erectile dysfunction associated with soy product consumption. Nutrition, 27(7-8), 859-862.
- Foster, M., & Samman, S. (2015). Vegetarian diets across the lifecycle: Impact on zinc intake and status. In Advances in food and nutrition research (Vol. 74, pp. 93-131). Academic Press.
- Prasad, A. S., Mantzoros, C. S., Beck, F. W., Hess, J. W., & Brewer, G. J. (1996). Zinc status and serum testosterone levels of healthy adults. Nutrition, 12(5), 344-348.
- Shemesh, A., Endevelt, R., & Levy, Y. (2011). Reversible Nutritional Hypogonadism in a 22-Year-Old Man. The American journal of medicine, 124(12), e1-e2.
- Hämäläinen, E., Adlercreutz, H., Puska, P., & Pietinen, P. (1984). Diet and serum sex hormones in healthy men. Journal of steroid biochemistry, 20(1), 459-464.
- Lamina, S., Okoye, C. G., & Dagogo, T. T. (2009). Therapeutic effect of an interval exercise training program in the management of erectile dysfunction in hypertensive patients. The Journal of Clinical Hypertension, 11(3), 125-129.
- Arteriosclerosis / atherosclerosis. (2018, April 24). Retrieved February 13, 2019, from https://www.mayoclinic.org/diseases-conditions/arteriosclerosis-atherosclerosis/symptoms-causes/syc-20350569
- Esposito, K., Giugliano, F., Di Palo, C., Giugliano, G., Marfella, R., D’andrea, F., … & Giugliano, D. (2004). Effect of lifestyle changes on erectile dysfunction in obese men: a randomized controlled trial. Jama, 291(24), 2978-2984.
- Bacon, C. G., Mittleman, M. A., Kawachi, I., Giovannucci, E., Glasser, D. B., & Rimm, E. B. (2003). Sexual function in men older than 50 years of age: results from the health professionals follow-up study. Annals of internal medicine, 139(3), 161-168.
- Gaskins, A. J., Mendiola, J., Afeiche, M., Jørgensen, N., Swan, S. H., & Chavarro, J. E. (2015). Physical activity and television watching in relation to semen quality in young men. Br J Sports Med, 49(4), 265-270.
- Nguyen, R. H., Wilcox, A. J., Skjærven, R., & Baird, D. D. (2007). Men’s body mass index and infertility. Human Reproduction, 22(9), 2488-2493.
- How common is infertility? (n.d.). Retrieved February 25, 2019, from https://www.nichd.nih.gov/health/topics/infertility/conditioninfo/common