There is spontaneous rupture of the Achilles tendon in an 18 year old male. It is most likely to be due to excess stress beyond -

ACHILLES TENDON RUPTURE: A ripping or popping sensation is felt, and often heard, at the back of the heel. This most commonly occurs in spos requiring an explosive push-off: squash, badminton, football, tennis, netball. The patient will often repo having looked round to see who had hit them over the back of the heel, the pain and collapse are so sudden.The typical site for rupture is at the vascular watershed about 4 cm above the tendon inseion onto the calcaneum. The condition is often associated with poor muscle strength and flexibility, failure to warm up and stretch before spo, previous injury or tendinitis and coicosteroid injection. REF:Apley&;s system of ohopaedics - 9th edn - pg no 615.