We examined the relationships between morphology and muscle-tendon dynamics of the quadriceps femoris muscle (QF) of 11 males using velocity-encoded phase-contrast MRI. Thigh muscle EMG and joint range of motion were first measured outside the MRI scanner during knee extension-flexion tasks that were performed at a rate of 40 times/minute with elastic bands providing peak resistance of 5.2 kp (SD 0.4) to the extension. The same movement was repeated inside the MRI scanner bore where tissue velocities and muscle morphology were recorded. The average displacement in the proximal and distal halves of the rectus femoris and vastus intermedius aponeuroses was different (p=0.049) reflecting shortening (1.6 %), but the tensile strain along the length of the aponeuroses was uniform. The aponeurosis behaviour varied among individuals and these individual patterns were best explained by the differences in relative cross-sectional area of RF to vastus muscles (r = 0.71, p = 0.014). During dynamic contraction considerable deformation of muscles in the axial plane caused an anatomic measure such as muscle thickness to change differently (decrease or increase) in different sites of measurement. For example, when analyzed from the axial images, the vastus lateralis thickness did not change (p = 0.946) in the frontal plane through femur but increased in a 45° oblique plane between the frontal and sagittal planes (p = 0.004). The present observations of the heterogeneity and individual behaviour emphasize the fact that single-point measurements do not always reflect the overall behaviour of muscle-tendon unit.