Strong ligaments and tendons are necessary for any activity that involves stress on the joints. Repeated muscle contractions stimulate ligaments and tendons to grow stronger and thicker. Connective tissue does not adapt to increased loading as quickly as muscle tissue, so patience and careful load selection are of paramount importance when training these structures.
To reduce the chance of injury during your workout make sure to warm up for 10 minutes with a mix of light cardio and low-intensity resistance training. If you are recovering from an injury, consult a physiotherapist or medical professional before starting any strength programme.
To strengthen the Achilles tendon, there are 3 key areas to focus on:
Basic strength training will help to build the Achilles tendon and calf muscles in tandem. Try using 3 sets of 10-15 repetitions of these movements
The lowering phase of a lift involves lengthening muscles and tendons while under stress. This is known as eccentric training, and it has been heavily studied for its beneficial effects on growth factor release in tendons, helping them to become thicker.
The eccentric phase of a calf raise can be emphasised for the Achilles tendon by raising yourself on two legs and lowering on only one. This is known as an eccentric calf raise. These can be challenging at first, so it's best to start with your body weight and build up from there. These can also be performed on a step in a smith machine.
If your sport or activity of choice involves using the Achilles dynamically, then it is important to condition the tendons for the specific stresses they will encounter. One example of how to do this for a running based activity is ankle hops. If your sport involves lots of directional change, include more variety such as lateral ankle hops.