In order to maintain (or improve) tendon strength and flexibility, the tendon must be exposed to loads greater than what the tendon routinely experiences. Anytime you stand, you are loading the Achilles tendon (AT)—but only in a narrow range of it’s total movement. Walking loads the AT in a greater range (ankle bends about 40 degrees each time you take a step), and running not only loads it through a greater range (60 degrees), but also at a higher intensity. (Standing is 50-100% of body weight (BW), walking 100%, and running 200-300% of BW).
For AT exercises to be effective, you must stretch through a greater range than 60 degrees, and strengthen at loads higher than 3 times BW. These are the exercises I recommend:
1) Deep squat-hold for 1 minute. Stretches AT through full range of functional use.
2) Elevated Single Leg Heel Raise-lift heel all the way up and down 20 times, each leg.
3) Heel Bounces-small bounces at end range for 1 minute.