1

In {1}, a physician mentions that testosterone injections increase the risk of tendon rupture. The controlled study {2}, based on medical histories from 142 experienced male bodybuilders age 35–55, concluded:

AAS (Anabolic-Androgenic Steroid) abusers, as compared to otherwise similar bodybuilders, showed a markedly increased risk of tendon ruptures, particularly upper body tendon rupture.

In the discussion section, {2} hypothesized that testosterone injection increase the risk of tendon rupture because "causes massive hypertrophy of muscles without causing any corresponding strengthening of the associated tendons":

The causes of AAS-associated tendon rupture are still incompletely understood. Two alternative (and not mutually exclusive) hypotheses should be considered. One possibility is that AAS use has little or no deleterious effect on tendons themselves, but merely causes massive hypertrophy of muscles without causing any corresponding strengthening of the associated tendons. Thus, the muscle may simply become too strong for its tendon, increasing the possibility of rupture in response to a sudden stress. Alternatively, it is possible that high doses of AAS, perhaps in conjunction with intense muscular exercise, may damage the structure of the tendons themselves, making them more vulnerable to rupture even in the absence of excessive stress. Evidence favoring the latter hypothesis comes from various animal studies, which have typically found that AAS exposure, usually in conjunction with exercise, led to collagen dysplasia, causing tendons to become stiffer and less flexible, with an increased crimp angle and earlier liability to failure.14, 21, 30–32, 34–39, 52 However, one human study using electron microscopy found no evidence of collagen fibril ultrastructural abnormalities in the ruptured tendons of two AAS users as compared to two non-AAS-using controls.9 Another recent study found no significant difference in maximal strain and toe limit strain in the patellar tendons of 8 long-term AAS users as compared to 8 experienced weightlifters reporting no AAS use, also arguing against the hypothesis of changes in collagen crimp pattern associated with AAS use.47 Thus the evidence for a direct toxic effect of AAS on human tendons remains somewhat inconclusive.

Although our study provides no direct evidence on the above issues, it is notable that we found a markedly increased risk of upper body tendon ruptures in AAS users versus non-using weightlifters, whereas the risk of lower body tendon ruptures was only modestly and non-significantly increased among AAS users. If indeed AAS use causes damage to human tendon architecture, one might predict that our AAS users, with histories of very extensive exposure to very high doses of AAS, would show a uniformly elevated prevalence of all types of tendon rupture throughout the body, rather than primarily an elevated risk of upper-body tendon ruptures. Therefore, our findings might be taken to weigh to at least some degree against a hypothesis of direct tendon damage, and might weigh more in favor of the simple theory that hypertrophied muscles can more easily break their tendons. In favor of the latter possibility, it is notable that AAS users are particularly prone to increase upper body musculature, leading to massively hypertrophied pectoralis, biceps brachii, and triceps brachii muscles, while often showing less of an effect on lower body musculature.43 Thus, it is conceivable that muscle hypertrophy alone might account for our findings without postulating an additional mechanism of AAS-induced tendon damage.

Since this study has been published, has there been any progress on the understanding of AAS-associated tendon ruptures?


References:

  • {1} https://youtu.be/qELlhoe9Nb8?t=4m10s ; VICE - Juiced Up - The Consequences of Steroids: SWOLE Ep. 3.
  • {2} Kanayama, Gen, James DeLuca, William P. Meehan III, James I. Hudson, Stephanie Isaacs, Aaron Baggish, Rory Weiner, Lyle Micheli, and Harrison G. Pope Jr. "Ruptured tendons in anabolic-androgenic steroid users: a cross-sectional cohort study." The American journal of sports medicine 43, no. 11 (2015): 2638-2644. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5206906/
2

I found a 2017 article pointing specifically to a case of AAS usage associated with a Bilateral Patellar Tendon Rupture, which mentions:

we suppose that combined AAS and exercise can increase tendon stiffness, predisposing to the rupture

Additionally, one of this paper's sources references a 2016 study in which they point out that:

Bilateral patellar tendon ruptures are rare. The majority of case reports describing bilateral patellar tendon ruptures have occurred in patients with predisposing factors to tendinopathy...

...careful history taking and physical examination is integral in ensuring a diagnosis is achieved for early primary repair.

So it seems that there is still not enough information and research done to fully determine why, but this is the theory developing as scientists examine more cases. A caveat is that both of the studies were case-studies of single individual men (ages 44 and 45 respectively), so there may be other factors that were not analyzed, considered, or observed.

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