Testosterone is a hormone that is produced in large amounts by males (and a little bit in females), in the testes and adrenal glands. High testosterone levels are associated with sexual performance, reproductive function, muscle mass, hair growth, aggressive, competitive behaviors, and other such manly things. Testosterone levels tend to peak at the age of 40, and slowly decline from there. Luckily, there are many things you can do to increase testosterone, so if you feel like your T levels could use a boost, you've come to the right place.
While the authors are justified in arguing that they found five significant results, some of their other claims are harder to defend. Smith points out that there’s a difference between a statistically significant result and a practically significant result. Two runners can have different times without one having a significant competitive advantage over the other. And while most in the track and field community would consider the two-second difference found between low-T 800 meter runners and high-T 800 meter runners to be significant, that’s only the authors’ best guess for the time difference—it could be a difference as small as a fraction of a second, or as large as four or five seconds. As Smith says, “the broader implications are unclear.”
The partition coefficient of the ester in question is important because is effects how long the drug itself stays in the system. If the testosterone transfers too quickly from the oil to the blood, the result is a sudden spike in testosterone which then rapidly drops once the dose has been used up. In the example of free testosterone injected into the muscle from a water suspension (as in Aquiviron, mentioned above), the testosterone is essentially immediately available to the bloodstream due to its low partition coefficient, and thus there is an immediate spike of testosterone which is used up quickly in the body.