I saw a post in the reddit flexibility forum and had a few comments to make:
First, understand that many yogas do not involve stretching at all
Yoga simply means to yoke or join the lower self with the higher self.
Bhakti Yoga is devotional yoga
it involves prayers and chanting and perhaps some prostrations. But by no means does it involve stretching. The Hare Krishna organization might be the largest and best-known bhakti organization.
Karma Yoga is action without attachment to outcome
Instead of doing acts for self-interest, when one performs a virtuous act without attachment to outcome, that is Karma Yoga. I practice Sivananda Yoga and their entire staff does not receive one penny for their work. You read that right: they work long hours every day and have nothing in their bank account to show for it. It’s a great way to develop detachment. Although some might think it’s a great way to be financially exploited.
Jnana Yoga is knowledge Yoga
realizing “god” through rational inquiry is the way of the Jnana (pronounced gee-yana) yogi.
Kriya Yoga involves moving energy up the spine
The amount of stretching in this is none.
OK, so what yoga involves stretching?
You may research raja yoga or hatha yoga for this. Raja yoga has 8 limbs, the 3rd of which is asana, or posture. “8 limbs” is literally ashtanga (ashta = 8). There is a particular ashtanga yoga formulated by K. Pattabhi Jois that has its home in Mysore, India. These practitioners demonstrate impressive feats of strength and flexibility. If you search on Youtube for “80 year old ashtanga yogi” you will see a person demonstrating exceptional strength and flexibility through Ashtanga Yoga.
Now, do the physical yogas improve stretching?
Absolutely. As someone in the thread said, hot yoga might be the fastest way to lubricate and loosen muscles. I’ve also found that to be the case.
But never forget the purpose of yoga
The purpose of yoga is to find out who you really are. It is not about improving what you are not but releasing you from mis-identification. All original yogas have that as their ultimate goal. Oddly enough, in the west, the real meaning and intent has often been lost and it is seen as a form of holistic fitness and nothing now.