The question, "Bro, how much do you lift?" may take on a new meaning when it comes to your sex drive. Going too hard at the gym for too long can shrink your fat, and something else — your libido. Researchers at the University of North Carolina in Chapel Hill found regularly doing more high-intensity workouts and endurance training is linked to a low sex drive, and possibly infertility.

"Exposure to higher levels of chronic intense and greater durations of endurance training on a regular basis are significantly associated with ... decreased libido scores in men," wrote the researchers, in the study published in Medicine and Science in Sports and Exercise.

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We all know exercise increases energy, reduces stress, and aids in weight loss. However, too much exercise can lower the number of sex hormones in the body, diminishing sexual desire. For example, in women it's easy to spot low sex hormones; those who overtrain tend to develop irregular menstrual periods, or stop having them altogether. This is part of the “female athlete triad,” which also includes osteoporosis and disordered eating. The hormonal imbalance may be triggered by physical stress, affecting a woman's interest in sex and her fertility.

Less is known about the effects of exercise, especially high intensity, on sexual desire and fertility in men. To study the associations between endurance exercise training and male libido, researchers recruited about 1,100 men to respond to an online poll about their sex lives, such as how often they thought about sex, and how often and how intensely they worked out. Most of these men were either runners, cyclists, or ameteur endurance athletes who were contacted through trade magazines.

The researchers categorized these men based on the duration and intensity of their workouts, such as short or long, and light, moderate or intense. Sex drive was also placed under high, moderate, or low libido.

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The findings revealed there's a tipping point when exercise starts to dampen sex drive. Those who trained at the lowest intensities were approximately seven times more likely to report a normal or high libido than those who trained at higher levels of intensity. The researchers also calculated duration of chronic training — total number of hours per week trained, multiplied by years of training. They discovered that those who trained the hardest or longest had decreased libido.

Why Libido Decreases After Exercise

It's too early to determine if too much exercise actually causes low libido, but it does suggest the two are linked. Dr. Anthony Hackney, lead author of the study, and a professor of exercise physiology and nutrition at the University of North Carolina, hypothesizes both physical fatigue and low testosterone levels after high intensity workouts may play an influential role.

It's known intense exercising training can lead to the onset of exercise hypogonadal male condition. This occurs when testosterone and the luteinizing hormone are suppressed. Exercise-hypogonadal condition is limited to men who have been persistently involved in chronic endurance exercise training for an extended period of time, such as years, but it’s not highly prevalent.

Read More: Everything You Need To Know About High-Intensity Interval Training

Hackney aims to find at what point exercise might start to lower some men’s libidos. Both moderate and light physical activity were associated in this study with relatively high libidos, he points out. He and his colleagues hope to conduct experiments that directly track exercise, hormone levels and libidos to learn more about their interactions.

They also aim to learn more about whether the intensity of the workouts or duration has the greater impact on male sex drive.

In regards to its role in fertility, Hackney suggests fertility specialists should ask men, along with women, whether and how much they exercise.

It's known exercise can cause temporarily lower sperm count in men when the body regularly becomes too overheated. Body temperatures that rise above 96 degrees can increase the likelihood sperm will die. Heat damages sperm, so if the body overheats during excessive exercise then this can have the same effect as a being in a hot tub or sauna.

Hackney and his colleagues conclude: "Clinicians who treat male patients for sexual disorders and, or counsel couples on infertility issues should consider the degree of endurance exercise training a man is performing as a potential complicating factor."

Sources: Hackney AC, Lane AR, Register-Mihalik J et al. Endurance Exercise Training and Male Sexual Libido. Med Sci Sports Exerc. 2017.

See Also:

4 Exercises To Treat Erectile Dysfunction For Men Struggling With Impotence

Exercise Can Reduce Older Men’s Risk For Serious Fall, But Not Women For Some Reason