In response to a couple of comments from yesterday's post- Ace has posted a great response. I have nothing to add really- his comment was perfect and he knows his stuff.
Reading your comments about stretching and yoga, I must say I agree with you. Yoga classes can be terrible places for people to work on "flexibility", especially endurance athletes.
I think the reasons for this are many but primarily come down to some personality differences between people drawn to endurance sports as a primary physical expression and those primarily drawn to yoga and the fact that very, very few yoga poses are actually stretches. At least in the traditional sense. Most poses people come to relate to yoga and stretching are merely preparations for strength and balance postures.
As a practice yoga's purpose is restore the body and clear the mind. I think you make some very good observations regarding your own body and flexibility. Given your experience training at very high levels of fitness, you already posses a body with strong muscle tissue. Strong muscles are typically flexible. So as you indicate you can put your palms on the floor in a forward fold without strain to the hamstrings.
There are several factors that allow this to happen. One of the most important and most over looked is core strength and integration. There is much going on in a forward fold but most essential for deepening the fold is engaging the core properly.
The reason for this is the forward fold is actually a handstand preparation where more and more weight is removed from the legs and placed into the palms until the hips are directly over the shoulders and the legs are lifted from the floor (you can see the same process in Olympic platform divers). The purpose isn't to "stretch" the hamstrings at all but to release them. Downward Dog works in much the same way, encouraging access to the core, releasing the hamstrings, and preparing the body for the forward fold, handstands and "floats" to seated postures or arm balances when done properly. I find this type of conditioning greatly impacts my running and cycling.
I think this is where yoga and stretching part company. Unfortunately a large number of yoga teachers fail to understand or articulate this distinction. Yoga is about creating body awareness and muscular access. These things can make you more "flexible". But this type of work is very, very different from stretching where the goal is merely to lengthen a muscle. Yoga is more about strength and coordinated muscle access.
One of the reasons I started teaching yoga classes specifically for endurance athletes is because I came to realize there are very few yoga teachers that understand what we endurance athletes are asking our bodies to do on a regular basis. The physical, emotional and mental demands are tremendous. Because of this I agree, someone going into a typical yoga class can get injured. But I'd also say that same person could injury themselves stretching as well.
Personally I have found yoga's emphasis on breath and the intelligent interaction between our bodies and our minds that is always taking place to be hugely beneficial in my training. But the benefit to which I refer has nothing to do with how "flexible" I am. The benefit I see is as simple as faster and more effortless swimming, biking, and running. But I suspect breathing and the extensive strength, core work and muscular integration that allowed this to happen came from working on things like headstands, handstands, and arm balances. I didn't really need yoga for this, but it provided a good framework to build in structure allowing me to gain access to this type of coordination.