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Proprioceptive Neuromuscular Facilitation

Leg stretch
This technique is used to lengthen muscles and increase range of motion immediately.

 PNF  is a set of stretching techniques commonly used in clinical environments to enhance both active and passive range of motion with the ultimate goal being to optimize motor performance and rehabilitation.
This technique is the the optimal stretching method when the aim is to increase range of motion, especially in short-term changes. 
Generally an active PNF stretch involves a shortening contraction of the opposing muscle to place the target muscle on stretch. This is followed by an isometric contraction of the target muscle.

          PNF can be used to supplement daily stretching and is employed to make quick gains in range of motion to help athletes improve performance. Aside from being safe and time efficient, the dramatic gains in range of motion seen in a short period of time may also promote compliance with the exercise and rehabilitation program.