If the center of gravity leans forward (1st image), the Achilles tendon is placed in a lengthened position, where the pressure from the heel bone becomes more severe with increased tension. Furthermore, the hip muscles are naturally displaced from their neutral position, making it difficult for them to fully function at their necessary potential. As a result, the muscles below the glutes such as the hamstrings or calf muscles have to compensate by working more (which will lead to overload on these particular muscles), making them tight. Tight calf muscles tend to pull on the Achilles tendon and the increased tension and compression of the heel increases the likelihood of developing tendon issues. (See the video below from 03:55)

What happens to the Achilles tendon if the center of gravity is tilted to one side (2rd image)? In this woman's case, her weight is shifted to the right and the outer side of her right calf muscles can be lengthened a little more. Similarly, the inner part of the calf muscles on the left side will be stretched out. Long-term exposure to the increased tension can actually make them tight as these muscles do not like to be stretched too much and cannot elongate endlessly. Tight calf muscles, in turn, start to pull on the Achilles tendon and this can increase its tension and compression by the heel bone.

Finally, the third physical feature that can put stress on the Achilles tendon is pelvis rotation (3rd image). This man's pelvis tends to rotate to the right when he is completely relaxed. This pelvic rotation also creates a similar rotational force in the lower limbs, which can act to twist/distort the Achilles tendon.

These body features mentioned above appear in combination rather than just one, and can stress the Achilles tendon, so make sure to do a program that balances your whole body.