Final answer:
Fibroblasts are located in the connective tissue proper of the Achilles tendon, where they produce collagen fibers to strengthen the tendon.
Step-by-step explanation:
Fibroblasts are a type of cell found throughout connective tissue proper, including the Achilles tendon. In the Achilles tendon, which is a fibrous connective tissue, fibroblasts are primarily responsible for producing the collagen fibers that give the tendon its strength and flexibility.
The Achilles tendon serves as a critical attachment between the plantaris, gastrocnemius, and soleus muscles and the calcaneus bone, facilitating movement of the ankle. Strands of collagen fibers in the tendon are aligned in parallel, which enables it to withstand the forces exerted during muscle contraction and movement, especially during activities like running and jumping.