Week 64: Contract and Relax?

I've wonder for a long time about standing forward bends (Uttanasana) and it's "sister", half forward bend (Ardha Uttanasana ). Over the years, sun salutations (Surya Namaskar) have been a common and frequent sequence in my practice. Yet, I needed to know more about these two basic and fundamental poses in the sequence.

This week's practice included multiple forward and half forward bends and it got me to thinking, what is the role of these poses. Why do they both exist? Is it that the half forward bend is just for someone who has tight hamstrings or is there more to it?

As an exercise physiologist, my brain goes straight to what is happening in the body. As most sun salutations start with a standing forward bend followed by a half forward bend then back to the forward bend, my initial thought was the pairing of the two is for the purpose of stretching the hamstring. The method would be through Proprioceptive Neuromuscular Facilitation (PNF) stretching. And more specifically, through the contract and relax PNF stretch. But is this the case?

My knowledge dictates that when stretching a muscle (i.e., the hamstring) and then forcing it into a contraction via the lift into half forward bend, it will then cause the muscle to relax via the golgi tendon organ (fancy name for a proprioceptive sensory receptor organ). The second forward bend is then able to move into a greater hamstring stretch due to the neuromuscular system reacting to the force of the contracted muscle.

The challenge was that I found minimal content online or off that supports my theory.

Is this what is actually happening? Educated guess or over thinking?

Nonetheless, the benefits of standing forward bends and half bends are not only stretching the hamstrings but it elongates the spine, stimulates the belly whereby it massages internal organs, tones liver, spleen, kidneys. It is also a pose used frequently as a rest between more strenuous poses. 

So, I don't have answers to my query but interesting to dissect these poses this week.

Do you know the answer?
LW