A small but unfortunate percentage of people who tear their Achilles tendon on one side will go on to tear the opposite side. The authors of this study evaluated medical records of 181 patients presenting with Achilles tendon ruptures to identify which specific risk factors were associated with contralateral Achilles tendon tears. The authors looked at all potential factors that might be associated with contralateral tearing including age, body mass index, occupation, blood type, underlying comorbidities, history of alcohol intake or smoking, injury mechanism, and even the use of fluroquinolone antibiotics and/or steroids.

The authors also considered the effect of occupational stress by evaluating individuals working in jobs requiring heavy physical labor. Of the 181 people studied, 5.5% went on to rupture the opposite Achilles tendon. Surprisingly, there was little correlation between alcohol intake, smoking, body mass index and/or age and the individuals most likely to tear the opposite Achilles tendon possessed type O blood, and/or were involved in occupations requiring excessive physical labor. People with type O blood were between 3 and 4 times more likely to tear the opposite Achilles tendon and individuals with physically stressful jobs were more than 5 times more likely to tear their opposite Achilles tendon. The connection between type O blood and tendon injuries is not as unusual as you might expect. In 1989 researchers from Finland (1) evaluated 749 patients presenting with 832 tendon ruptures (including 292 Achilles tendon ruptures) and found that people with type O blood sustained 71% of all tendon ruptures and reruptures. Keep in mind that only 43% of the population has this blood type and to this day no one understands the exact mechanism explaining why type O blood correlates so strongly with tendon ruptures. My take home from this research is that if you have blood type O and/or are exposed to heavy occupational stresses, you should consider doing preventive Achilles exercises, such as the long-duration, high-force isometric contractions described in the prior article, as this might decrease your potential for both injury and/or reinjury.

1. Jozsa L, et al, The role of recreational sport activity in Achilles tendon rupture: A clinical, pathoanatomical, and sociological study of 292 cases. Am J Sports Med 1989.