A recent study conducted at Johns Hopkins University found that testosterone may play a protective key role against knee injuries, such as anterior cruciate ligament (ACL) tears. Using an animal model, the study analyzed how different levels of testosterone affect load-bearing and ligament strain. The authors found that testosterone contributes to ACL strength in males, which may suggest why ACL injury is two to 10 times more common in women.

Previously, the study author, William Romani, Ph.D., identified the correlation between high levels of circulating estrogen and weakened ACL strength in a female animal model (2). Estrogen may contribute to higher ACL injury rates due to its ability to remodel the ligament tissue and weaken the overall structure of the ligament (3). Together, this work suggests that sex hormones, such as estrogen and testosterone, exert different effects on ligament strain and stress and may explain why women have a higher rate of total knee replacement than men (4). 

In the future, the findings of this study may allow physicians, physical therapists, and athletic trainers to work together to observe cycling hormone levels to identify those who may be at greater risk of injury and could benefit from targeted strength training as a preventative measure (either in individuals with higher than normal levels of estradiol or lower than normal levels of testosterone) (1).

References:
1. Romani et al., The Knee. 2016. Epub ahead of print.
2. Romani et al., J Womens Health (Larchmt). 2003 Apr;12(3):287-98.
3. Liu et al., Am J Sports Med. 1997;25(5):704-9.
4. Centers for Disease Prevention and Control.