In a prospective study of risk factors for Achilles tendinopathy among four induction cycles of infantry recruits, 95 out of 1405 recruits, (6.8%) were found to suffer from Achilles tendinopathy. In more than 94% of the cases, the tendinopathy was considered to be paratendinitis. Training season had a statistically significant effect on the incidence of Achilles paratendinitis with 3.6% suffering in the summer and 9.4% in the winter (p = .001). This increased risk for Achilles paratendinitis in cold weather outdoor training can be explained by a fall in temperature of the Achilles paratenon whose membranes are rich in mucopolysaccharides and serve as a lubricant for gliding of the tendon and epitenon. Decreased temperature may increase the viscosity of the lubricant and thereby increases friction and risk for Achilles paratendinitis. This same relationship illustrates why "warming up" before exercising may be important in lowering the incidence of Achilles paratendinitis.