At the end of the study, testosterone blood levels in the men who had received supplements was nearly twice that of the other men. And they had a slight increase in lean body mass, which is a common motivation for taking testosterone. But for the men who did resistance training, their functional fitness, as measured by attributes such as upper- and lower-body strength and flexibility, and tests such as climbing stairs and distance covered in a six-minute walk, didn't improve any more than that of the weight-training men who didn't take testosterone.
This study supports the idea that our bodies function as an integrated whole rather than a set of distinct systems that can be precision-targeted. While declines in testosterone levels are common with aging, they can be partly offset by regular bouts of high-intensity exercises, such as sprints, hill workouts and weight training, that spur testosterone production.