Abstract
PURPOSE: This study aimed to assess the influence of knee joint cooling on the in vivo mechanical properties of the patellar tendon. METHODS: Twenty young, healthy women volunteered for the study. B-mode ultrasonography was used to record patellar tendon elongation during isometric ramp contraction of the knee extensors (5-7 s, 90° knee angle) and calculate tendon stiffness. Skin temperature was measured by infrared thermometry. Data were acquired before and after 30 min of local icing of the knee joint and compared by paired samples t-tests. RESULTS: After cold exposure, skin temperature as measured over the patellar tendon dropped by 16.8 ± 2.0 °C. Tendon stiffness increased from 2189 ± 551 to 2705 ± 902 N mm(-1) (+25 %, p = 0.007). Tendon strain decreased by 9 % (p = 0.004). A small, albeit significant reduction in maximum tendon force was observed (-3.3 %, p = 0.03). CONCLUSIONS: Knee cooling is associated with a significant increase in patellar tendon stiffness. The observed tendon stiffening may influence the operating range of sarcomeres, possibly limiting the maximal force generation capacity of knee extensor muscles. In addition, a stiffer tendon might benefit rate of force development, thus countering the loss in explosiveness typically described for cold muscles.