What exercise/activity would increase circulating testosterone to the greatest degree?

The Romanian deadlift is particularly effective at increasing circulating testosterone levels due to its involvement of large muscle groups, specifically the posterior chain, which includes the hamstrings, glutes, and lower back. This exercise typically allows for higher loading and more intense effort compared to exercises that isolate smaller muscle groups.

Resistance training, especially through compound movements like the Romanian deadlift, promotes higher levels of hormonal response, including testosterone release. This is primarily because the large muscle mass engaged during these types of exercises puts significant stress on the body's systems, prompting a rise in anabolic hormones necessary for recovery and muscle growth.

Additionally, movements that involve multiple joints and greater overall loading tend to elicit a more pronounced endocrine response. Therefore, exercises like the Romanian deadlift provide an optimal environment for testosterone secretion when compared to less intense or isolated movements.