The calf stretch is important if the knee has been held in flexion for some time, perhaps after a long spell on crutches.



In case you cannot see the video, here is a still sequence -

calf stretch Stand opposite a wall, with your fingers supporting you on the wall.
calf stretch Step back on the one leg. Lean forward, stretching the back of the rear leg's calf and ankle. Hold for 20 seconds. Repeat five times.