EVIDENCE OF TIME-DEPENDENT TENSILE RESPONSE IN INTACT HUMAN TENDON
Abstract
The present study was performed to establish whether intact human tendons exhibit time-dependent tensile properties, as they do in the in vitro state. Measurements were taken in seven men and involved ultrasound-based recording of the gastrocnemius tendon elongation during three sets of five repeated isometric plantarflexion contractions elicited by tetanic electrical stimulation. The plantarflexion moment corresponding to the tendon elongation in the fifth contraction presented a pattern dependent on the voltage applied: it was approximately constant when applying 50% of maximal voltage, but it decreased curvilinearly as a function of contraction number when applying 70 and 100% of maximal voltage, reaching in the fifth contraction 84% of the plantarflexion moment corresponding to the elongation examined in the first contraction. These results suggest that, once a threshold tendon elongation is undergone, in vivo tendons may exhibit substantial viscoelasticity. The present findings have implications for muscle and joint function and need to be accounted for by musculoskeletal models.
