"Compared to Ranger school, combat was easy..."

The United States Department of Defense, at Defense Secretary Pete Hegseth's direction, recently announced a controversial plan to begin mandatory testosterone testing for all male service members age 30 years and older.  Secretary Hegseth has previously stated that he believes that screening troops for "testosterone deficiency" is necessary to keep them operating at their "absolute best".  Sean Parnell, a spokesperson for the Pentagon said that "by proactively identifying and treating suboptimal hormone levels," we will "invest in the health of its warfighters, strengthen their performance, and maximize force readiness."  The plan for the moment excludes female members in the military.

The Pentagon's plan is controversial because (1) medical professionals currently do not recommend universally screening testosterone levels in men (testing is recommended only for those individuals who report signs and symptoms of decreased testosterone, including low libido and depressed mood) and (2) there is limited, if any, evidence to suggest that replacing testosterone has any appreciable effect on energy, vitality, physical function, or cognition (testosterone replacement can, however, improve sexual function and bone density).  Importantly, the Pentagon's plan does acknowledge the limited medical benefits of testosterone replacement, and the new policy does not make testosterone replacement mandatory.

As I was reading about this new Pentagon policy, I couldn't help but think of a study that I read a few weeks ago showing that men and women respond differently to arduous physical training.  In addition, there is evidence to suggest that certain high stress military environments can deplete the body's normal testosterone levels, at least in men.  For example, consider what participating in the Ranger Training Course (RTC) does to a soldier's body.  RTC (also known as "Ranger School") is a rigorous 62 day small unit tactics and leadership course designed to push soldiers to their absolute extremes.  The mixed martial artist and Ranger Tim Kennedy reportedly once described RTC as "a place that starves you and denies you sleep for over two months."  Colonel Robert "Tex" Turner claimed that he once woke up from a dream while serving in Vietnam and said, "I woke up in my foxhole in a cold sweat. I had a nightmare that I was still in Ranger School. Thank God that I was in Vietnam. Compared to Ranger School, combat was easy."  Several studies have shown that soldiers have progressively lower levels of testosterone and growth hormone during RTC, and by the end of their training (if they make it to the end - only about 50% of soldiers complete the entire training course), most soldiers have testosterone levels that are consistent with a medical diagnosis of secondary hypogonadism (if you are interested, the links to these scientific studies are here, here, and here).

Historically, female soldiers were not allowed to complete the Ranger Training Course.  However, since the first two women - Kristen Griest and Shaye Haver - graduated from RTC in 2015, approximately 175 female soldiers have completed the training to become eligible to wear the Ranger Tab on their left upper shoulder.  Accordingly, Samantha Goldenstein and colleagues conducted a study to determine if females would experience a similar decrease in metabolic, growth, and sex hormones during RTC.  The results of their study were published this past year in the July issue of the Journal of Applied Physiology.

Goldenstein and her team studied 26 men and 10 women who completed RTC.  They measured body composition, resting energy expenditure, energy balance, and blood and urine levels of key metabolic, growth, and sex hormones at baseline (prior to starting RTC) and then at periodic intervals during the three different phases of training (general field, mountain, and swamp training).  Overall, as expected, energy balance was negative in all three phases, which resulted in an average loss in body mass and decreased resting energy expenditure throughout the entire course compared to baseline.  However, males experienced a larger negative energy balance in the first two phases (but not the third phase) compared to females.  

Thyroid hormone remained suppressed during all three phases in male soldiers, but only during the second phase (mountain phase) in females.  Growth hormone was suppressed in all three phases in both males and females.  Similar results have been reported in a study of females participating in a 61-day Antarctica expedition (similar decreases in body mass and resting energy expenditure, but no significant change from baseline in thyroid hormone).  Female sex hormones (estrogen, progesterone, and testosterone) only changed during phase 2 (mountain phase) of RTC compared to baseline.  Male testosterone levels were significantly lower than baseline during the first two phases (but not phase 3).  Finally, inflammatory markers did not change significantly in either males or females (this may be due to the transient nature of the increase in inflammatory markers associated with acute exercise).

Goldenstein and colleagues conclude that "Females exhibited minimal alterations of physiological status that were largely phase-specific, whereas males demonstrated consistent changes in many markers of health across the course, despite experiencing similar energy deficits."  They go on to state that "male physiology may disproportionately be affected in multistressor environments." 

So, what does all of this mean?  First, in regards to the Pentagon's new policy of measuring testosterone levels in male soldiers, marines, sailors, and airmen, the timing of when testosterone levels are measured will matter a great deal.  Measuring testosterone levels following a lengthy deployment or period of arduous training would not make sense, as testosterone levels would be expected to be lower than normal at these times.  Second, males and females clearly react differently to chronic stress, and further information is required to help support the overall health of our military members.  Third, we need to determine the impact of these changes in endocrine function on the overall health with additional studies.  To that end, this same group recently published a study on the sex differences in physical performance, sleep, and psychological response to RTC (see their follow-up study here).