Flexibility in soccer, a more technical look

• muscles
• connective tissues
• joint capsule
• ligaments
• tendons
• skin
• adipose tissue (fat)

a. Stretch (myotic) reflex
The myotic reflex is a direct result of stimulation of the muscle spindle, which sends information to the central nervous system concerning the degree of stretch upon the involved muscle and the exact number of motor units needed to contract in order to overcome stretch.
When a muscle is ballistically stretched, it responds with a contraction whose amount and rate vary directly with those of the causative stretch.
When a muscle is statically stretched, this reflex is inhibited.
This inhibition is initiated by the Golgi Tendon Organ, as a protective mechanism to avoid injury.

b. Reciprocal inhibition
This is a neuromuscular function that inhibits (relaxes) one set of muscles when the antagonist (opposing muscles) are contracting (proprioceptive neuromuscular facilitation--P.N.F--is based on this function).
When this mechanism dysfunctions, with both agonists and antagonists contracting simultaneously a muscle strain (torn fibres and spasm) results.