Changes in the mechanical properties of tendon structures in lower limbs during repetitive contractions in male long-distance runners.

The purposes of this study were to compare mechanical properties of tendon structures during single and repetitive contractions between long-distance runners (LDR) and untrained males (UTM) and to verify the relationship between changes in mechanical properties of tendon structures during repetitive contractions and running performance in LDR. Mechanical properties of tendon structures of vastus lateralis (VL) and medial gastrocnemius (MG) muscles were measured during single contraction. In addition, changes in mechanical properties of VL and MG tendon structures were measured during 20 min of repetitive contractions. During single contraction, maximal elongation of tendon structures was significantly lower in LDR than in UTM for VL, but not MG. During repetitive contractions, hysteresis of VL and MG tendon structures increased significantly for both groups. In LDR, the relative change in hysteresis of MG tendon structures, but not VL, during repetitive contractions was significantly correlated with the best official record in the 5000-m race. In conclusion, LDR exhibited lower extensibility of tendon structures for VL compared to UTM, while both LDR and UTM showed significant increases in hysteresis of VL and MG tendon structures during repetitive contractions. Furthermore, LDR with higher competitive performance showed a lower increase in hysteresis of tendon structures for MG during repetitive contractions.