title: The time course of in vivo recovery of transverse strain in high-stress tendons following exercise.
abstract: OBJECTIVE
  To evaluate the time course of the recovery of transverse strain in the Achilles and patellar tendon following a bout of resistance exercise.
  
  
  METHODS
  Seventeen healthy adults underwent sonographic examination of the right patellar (n=9) and Achilles (n=8) tendons immediately prior to and following 90 repetitions of weight-bearing quadriceps and gastrocnemius-resistance exercise performed against an effective resistance of 175% and 250% body weight, respectively. Sagittal tendon thickness was determined 20 mm from the enthesis and transverse strain, as defined by the stretch ratio, was repeatedly monitored over a 24 h recovery period.
  
  
  RESULTS
  Resistance exercise resulted in an immediate decrease in Achilles (t7=10.6, p<0.01) and patellar (t8=8.9, p<0.01) tendon thickness, resulting in an average transverse stretch ratio of 0.86±0.04 and 0.82±0.05, which was not significantly different between tendons. The magnitude of the immediate transverse strain response, however, was reduced with advancing age (r=0.63, p<0.01). Recovery in transverse strain was prolonged compared with the duration of loading and exponential in nature. The average primary recovery time was not significantly different between the Achilles (6.5±3.2 h) and patellar (7.1±3.2 h) tendons. Body weight accounted for 62% and 64% of the variation in recovery time, respectively.
  
  
  CONCLUSIONS
  Despite structural and biochemical differences between the Achilles and patellar tendon, the mechanisms underlying transverse creep recovery in vivo appear similar and are highly time dependent. These novel findings have important implications concerning the time required for the mechanical recovery of high-stress tendons following an acute bout of exercise.
authors.affiliation: Faculty of Health Sciences and Medicine, Bond University, , Gold Coast, Queensland, Australia.
authors.forename: Scott C
authors.initials: SC
authors.lastname: Wearing
authors.forename: James E
authors.initials: JE
authors.lastname: Smeathers
authors.forename: Sue L
authors.initials: SL
authors.lastname: Hooper
authors.forename: Simon
authors.initials: S
authors.lastname: Locke
authors.forename: Craig
authors.initials: C
authors.lastname: Purdam
authors.forename: Jill L
authors.initials: JL
authors.lastname: Cook
mesh_terms: D000125:Achilles Tendon / Q000293:injuries* / Q000648:ultrastructure; D000328:Adult; D012090:Cumulative Trauma Disorders / Q000000981:diagnostic imaging / Q000534:rehabilitation; D015444:Exercise / Q000502:physiology; D064368:Healthy Volunteers; D006801:Humans; D018482:Muscle, Skeletal / Q000502:physiology; D017847:Patellar Ligament / Q000293:injuries* / Q000648:ultrastructure; D020127:Recovery of Function / Q000502:physiology; D055070:Resistance Training / Q000379:methods*; D013180:Sprains and Strains / Q000000981:diagnostic imaging / Q000534:rehabilitation*; D014463:Ultrasonography; D016474:Weight-Bearing / Q000502:physiology