Some studies suggest that running can increase testosterone levels, while others indicate the opposite. To understand this better, we need to consider the intensity and duration of the running activity. Overtraining as you'd expect can depress testosterone levels, in the same way not getting enough sleep or calories can, but there's still more to it than that.
It's also important to state that there is a difference between free and total testsoterone. The short version is that Free Testosterone, is the amount your body can use, that isn't being used to simply balance out other hormones, and Total Testosterone, which is as you'd assume the complete total.
And many studies that show testosterone levels decrease after running or similar excersise have also noted that free testosterone remains similar, suggesting that the increase in cortisol balances out by suppressing other hormones as well as testosterone.
There is also a lot of suggestion that in trained and healthy populations, testosterone fluctuations as a result of excersise are relatively short lived, with the body adjusting accordingly. The increases seem to be more prevelant in men who train or run regularly.
It's also worth noting that a lot of the benefits of running to testosterone may simply not apply straight away, there is a lot of evidence that when it comes to overweight individuals, excersise oddly has a deflating effect on testosterone in the short term. Particularly for endurance running. That said losing weight (which of course excersise will help with) will raise testosterone in the long term. This is important to note when it comes to reading studies on running and testosterone, as a lot were conducted on sedentary men.
There isn't a very simple answer unfortunately, and as simple as we can make the answer is: yes running can raise testosterone, but only shortly after finishing a high intensity work out for a brief amount of time, longer depresses testosterone. And there are a number of factors that can impact the overall increase. There are also factors such as weight and age which seem to greatly impact testosterone levels. The largest testosterone increases were also seen in men who train regularly, although these were again short lived, lasting less than an hour after excersise.
And there's still more to it than that, unfrotunately the relationship between excersise and testosterone, particularly running isn't a simple one.
High-Intensity Running and Testosterone
Research has shown that high-intensity running, such as sprinting or interval training, can significantly increase testosterone levels. A study involving handball players who performed four 250-meter sprints at 80% of their maximum speed with rest intervals in between showed a significant increase in testosterone levels. This type of exercise, known as High-Intensity Interval Training (HIIT), creates an anabolic state similar to weightlifting, promoting muscle growth and potentially increasing testosterone production. 
Further studies have shown that higher-intensity endurance exercises, such as running at maximum intensity or near-maximum intensity, can lead to significant increases in testosterone levels immediately after exercise. For example, a study by Galbo et al. (year) found that young healthy men experienced a significant increase in testosterone levels (~31%) after 40 minutes of maximum intensity treadmill running. 
And this seems to apply to trained individuals as well with further studies showing that testosterone levels increase only after a certain duration or intensity threshold is reached. For instance, Kraemer et al. (year) reported that in well-trained runners, testosterone levels increased only after 5 minutes of running at 90% of their maximum oxygen uptake (VO2max). This suggests that both intensity and duration are important factors in eliciting a testosterone response to endurance exercise. 
Being Overweight, Running and Testosterone
Some studies suggest that exercise may have a blunted effect on testosterone levels in overweight and obese individuals compared to lean individuals. For example, Rubin et al. (year) found that although both lean and obese individuals experienced an increase in testosterone levels after resistance exercise, the increase was lower in obese men. It is possible that factors such as adiposity, inflammation, and impaired vasodilation in the testes may contribute to the altered hormonal response in overweight and obese individuals. 
Endurance Running and Testosterone
On the other hand, endurance running at a steady pace for longer durations may slightly decrease testosterone levels. Prolonged endurance workouts can lead to an increase in cortisol, a hormone released in response to stress.  Higher cortisol levels have been associated with decreased testosterone production. Therefore, it is important for endurance athletes to monitor their testosterone levels and ensure adequate rest and recovery to maintain hormonal balance.
The Study Showing Endurance Training Decreases Serum Testosterone Levels in Men
Another study conducted by Wheeler et al. (1991) aimed to determine how endurance training, specifically running, affects androgen levels in previously sedentary males. Over a period of six months, 15 sedentary men underwent endurance training and increased their weekly running mileage to an average of 56 km per week.  The results of the study showed a significant decrease in serum total testosterone and free androgen index levels. Prolactin (PRL) and cortisol, two hormones associated with stress, also decreased, while LH (luteinizing hormone) and FSH (follicle-stimulating hormone) remained unchanged. Interestingly, the decrease in testosterone levels was not related to changes in LH pulsatile release, weight, or increased cortisol levels. There have been further studies which have shown similar results.
How Long is Testosterone Raised After Running
While Running can acutely increase testosterone levels, the sustainability of this increase is an important consideration. Several studies have shown that the increase in testosterone levels after exercise is not sustained beyond a certain period.
For example, Manesh et al. (year) found that the increase in testosterone levels after endurance exercise was not sustained at 20 minutes into the recovery period.  Daly et al. (year) also reported a significant decrease in testosterone levels 90 minutes after endurance running,  despite rapid increases immediately after exercise. These findings suggest that the acute increase in testosterone levels may be transient and short-lived.
Think about how you feel after completing a good hard workout, that feeling of accomplishment could partially be linked to a testosterone spike.
Optimizing Testosterone Levels through Running
While the relationship between running and testosterone levels may be complex, there are strategies you can implement to optimize testosterone production while incorporating running into your fitness routine.
Incorporate High-Intensity Interval Training (HIIT)
To stimulate testosterone production, incorporate high-intensity interval training into your running routine. This involves alternating between short bursts of intense effort and periods of rest or lower intensity. For example, you can perform sprints at maximum effort for 30 seconds, followed by a 1-minute recovery period. Repeat this cycle for several rounds. HIIT not only boosts testosterone levels but also helps improve cardiovascular fitness and burn calories. This has also been shown to be the case in sedendary men. 
Include Strength Training
In addition to running, incorporating strength training exercises can further enhance testosterone production. Strength training exercises, such as weightlifting or bodyweight exercises, stimulate muscle growth and can lead to increased testosterone levels. Focus on compound exercises that target multiple muscle groups, such as squats, deadlifts, and bench presses. Research has shown that acute resistance exercise can cause an increase in testosterone levels immediately after exercise. For example, a study by Wheeler et al. (year) found that men who performed heavy resistance exercises experienced a significant increase in testosterone levels post-exercise. The magnitude of the increase may depend on factors such as the muscle mass involved and the intensity of the exercise. Involvement of larger muscle masses and higher exercise intensities tend to elicit greater testosterone responses. 
Prioritize Rest and Recovery
To maintain optimal testosterone levels, it is crucial to prioritize rest and recovery. Overtraining and excessive exercise can lead to increased cortisol levels and decreased testosterone production. Make sure to include rest days in your training schedule and listen to your body's signals for adequate recovery. Quality sleep, stress management techniques like mindfulness and deep breathing, and a balanced diet are also essential for hormonal balance and overall well-being. 
Maintain a Healthy Lifestyle
While running can contribute to testosterone production, it is important to support your body's overall health through a balanced lifestyle. This includes consuming a nutritious diet that includes foods rich in essential nutrients like protein, healthy fats, vitamins, and minerals. Adequate hydration is also important for optimal hormone function. Avoid excessive alcohol consumption and prioritize stress management techniques to keep cortisol levels in check. [12,13]
The Evidence That The Testosterone Increase After Excersise Doesn't Stick Around
In a study conducted by Hawkins et al. (2011), the effects of long-term aerobic exercise on serum sex hormones in middle-aged to older men were examined. The study involved 102 sedentary men aged 40-75 years who were randomly assigned to either an exercise intervention or a control group. 
The exercise intervention consisted of a 12-month program that included moderate to vigorous-intensity aerobic activity for 60 minutes per day, six days per week. The results of the study showed that DHT (dihydrotestosterone), a potent form of testosterone, increased significantly in the exercisers compared to the controls. Additionally, sex hormone-binding globulin (SHBG), a protein that binds to testosterone, also increased in the exercisers. However, there were no significant differences in total testosterone, free testosterone, or other androgens between the two groups.
Possible Mechanisms: Why Running May Boost Testosterone
While the studies mentioned above indicate that running may not directly increase testosterone levels in men, there are several possible mechanisms through which running can still have a positive impact on testosterone production and overall hormonal balance.
Weight Loss and Body Composition - Running is a high-calorie burning exercise that can contribute to weight loss and improved body composition. Excess body fat is associated with lower testosterone levels in men, as adipose tissue can convert testosterone into estrogen. By reducing body fat through running, men may experience a relative increase in testosterone levels.
Reduced Stress and Cortisol Levels - Chronic stress and elevated cortisol levels can negatively impact testosterone production. Running, like any form of exercise, can help reduce stress and promote the release of endorphins, which are known as "feel-good" hormones. By managing stress and cortisol levels, running may indirectly support healthy testosterone production.
Enhanced Overall Health and Well-being - Regular running and exercise contribute to overall health and well-being. It improves cardiovascular health, enhances insulin sensitivity, and reduces the risk of chronic diseases such as obesity, diabetes, and heart disease. Optimal health and physical fitness are often associated with balanced hormone levels, including testosterone.
Reasons Why Running May Not Boost Testosterone
While running offers numerous health benefits, it's important to note that the impact on testosterone levels may vary among individuals. Here are a few reasons why running may not directly increase testosterone in some men:
Individual Variations - Individual variations in hormonal response to exercise exist. Some men may experience a more substantial increase in testosterone levels from running, while others may not see a significant change. Factors such as genetics, age, baseline hormone levels, and overall health can influence the individual response.
Duration and Intensity of Running - The duration and intensity of running may play a role in testosterone response. Short bursts of intense running, such as sprints or high-intensity interval training (HIIT), may have a more potent impact on testosterone compared to long-distance endurance running. However, more research is needed to fully understand the relationship between running intensity and testosterone levels.
Recovery and Rest - Proper recovery and rest are crucial for hormone balance. Overtraining, undernourishment (particularly if you miss out on certain vitamins like zincor magnesium whilst dieting) or inadequate rest periods between running sessions can lead to elevated cortisol levels and potential hormonal imbalances. It's essential to listen to your body, incorporate rest days, and prioritize recovery to optimize testosterone production.
Does Running Increase Testosterone?
In conclusion, the relationship between running and testosterone levels is complex and depends on various factors such as intensity, duration, and individual physiology. High-intensity running, such as sprinting or HIIT, can increase testosterone levels briefly. However, prolonged endurance running may slightly decrease testosterone levels due to increased cortisol production. In reality any long term improvements to testosteorne are likely to be in relation to improved body composition. 
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2 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7739287/
3 - https://pubmed.ncbi.nlm.nih.gov/32158429/
4 - https://pubmed.ncbi.nlm.nih.gov/10192824
5 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8555925/
6 - https://pubmed.ncbi.nlm.nih.gov/1899423/
7 - https://pubmed.ncbi.nlm.nih.gov/17006802
8 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9312330/
9 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5510446/
10 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4870831/
11 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7005256/
12 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6761906/
13 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6266690/
14 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3040039/
15 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3667256/