Tendons are viscoelastic anatomical links between muscles and bones; Their primary role is the transmission of contractile force onto a joint, to enable movement. To fulfill this role, tendons must be sufficiently stiff. Mechanical stiffness is important when considering the role of either tendon or aponeurosis on the mechanical output of muscle contraction (1). It has previous been shown that the Vastus Lateralis aponeurosis stiffness is positively correlated to the rate of torque development (RTD) (2), however it is also important to consider the in series patellar tendon, since it is this tendon which is distally attached to the tibia, thus enabling knee extension movement . In addition it is known that tendons adapt to the mechanical loading they habitually undergo, by becoming stiffer or more compliant when chronic loading increases or decreases, respectively (1). The research has investigated the relationship between: 1) patellar tendon stiffness and rate knee extension torque development ,(RTD) and 2): patellar tendon stiffness and knee extension maximal voluntary contraction (MVC). Eight healthy young males (24±5yrs, 174±4cm, 72.38±10kg) were recruited for an 8 week training study. Baseline measures of patellar tendon stiffness derived from combining dynamometry and ultrasound scanning in vivo, knee extension MVC and RTD were obtained at 90° knee joint angle. RTD was assessed at 3 time variables 0 – 50ms, 0 – 200ms and 0 – 2/3 maximal force (F2/3). Pearson’s correlation was applied to the variables with a significance level of P<0.05. Patellar tendon stiffness, assessed at both maximal force and the highest common force to all participants, was significantly correlated to RTD obtained at 0-50ms (r2=0.75 and 0.58 respectively). However, this correlation was absent at either of the later time points, 0-200ms or 0-F2/3, when compared to patellar tendon stiffness at maximal or highest common force. Nonetheless, patellar tendon stiffness at maximal force and highest common force was also significantly correlated to MVC (r2=0.70 and 0.69 respectively). The above results indicate that tendon stiffness is an important contributing factor in the early stages of force transmission (50ms), which indicates that after the first 50ms as the tendon is pulled by the muscle, the tendon becomes an effective mechanical link for contractile force transmission and joint movement. Additionally, the high correlation between tendon stiffness and MVC indicates that differences in tendon stiffness largely reflect the differences in the maximum tensile force applied by the in-series muscle, despite maximum muscle forces not being applied often in daily activities. It is of interest to establish whether the proportionality between stiffness and MVC also applies between tendon and muscle dimensions.