This is one of many joint strengthening exercises I've used with clients. An exercise as simple as this can work wonders in building strength. Often smaller areas are overlooked in fitness training, but when you think about it your ankle joint takes a lot of stress over a typical day!
This exercise is a way of specifically targeting the ankle, and this was an exercise I'd used to aid the recovery of a client who had suffered a pilon fracture. This is a light resistance band with a resistance of up to 16 kilo's depending on the tension you apply. Resistance bands are not exact in resistance measurements, but have proven themselves time and time again in fitness training to be very useful.
This flexion and extension movement is just one direction, as I also incorporated reps to the left and right also. You can do this with both ankles at a time too. The position of the band can be altered on the sole of the foot for varying resistance patterns.
Remember as with all resistance bands, use safely! Avoid any banded exercise that pull towards your face in case of any mishaps or breakages. Resistance bands take a lot of punishment and do wear out. Make sure if you use one, that it is in good condition.