Stretching and muscle activity

Jules Mitchell's Yoga blog is a great resource. Go check it out!
As a biomechanist drawing directly from her experience of movement (specifically in the yoga sphere) she is questioning the common aphorisms of asana instruction and applying modern understandings of the human body in movement to this practice. Its fascinating and very useful.

Here's a little piece...click here to read the rest.

Proprioceptive Neuromuscular Facilitation (PNF) describes a stretching style that recruits muscle activation of the target muscle somewhere during the stretching process, usually right before. There are at least 9 different methods with slightly varying techniques and durations of contractions (concentric, isometric, and eccentric), holding times and subsequent relaxation/stretching procedures. A detailed review of the methods is too much for this post, so just understand the PNF involves muscle contraction followed by muscle relaxation – often referred to as “contract relax”. 

The most common method of PNF stretching that I have encountered in the world of yoga comes in the form of an “adjustment” by the teacher. For example, during a supine single leg hamstring stretch (Supta Padangusthasana or Recline Big Toe Pose) the teacher provides resistance by firmly holding the leg while the student strongly contracts her hamstring for 6 seconds, pushing leg against the direction of the stretch. The teacher then instructs the student to relax and the teacher passively stretches the student into a new and greater range of motion. Everyone is impressed by how effective the method is – the teacher is brilliant and the student is pleased by her sudden flexibility.

Unfortunately, the momentous increase in range of motion is transient. It is temporary. Within hours ROM will be what it was. The acute improvement of ROM during PNF stretching is really just an illusion. No biomechanical adaptations to the tiss ues occured instantaneously. Short tissues did not suddenly become long. So what happened?