Recently, at a large dance teacher's convention, I was fortunate enough to have time off from teaching to both take classes from other teachers and to observe dancers and teachers in class. One thing that struck me was the lack of focus on proper alignment in starting positions. While these often subtle differences don't usually cause an injury, they do set the body up for less than optimal movement - why would we want to prepare our students for class this way?
Since many warm ups for all ages are done sitting on the floor, I wanted to look at what happens with different body positions and cues in a commonly used position - knees bent, soles of the feet together.
It used to be quite common to see dancers holding their feet, fortunately this trend seems to be disappearing. Holding the feet will generally cause the dancer to sickle their foot and ankle in this position. As it's important to be anatomically accurate with your students, please don't tell them to hold their feet if you really meant their ankles, especially with our younger dancers just learning their body parts, this can cause a lot of confusion.
The next thing to think about is, is having the dancers hold their ankles really any better? It is for the alignment of the foot and ankle, but let's look further up the body to see what's happening. For many students, holding onto their ankles will require them to anteriorly tilt their pelvis (tipping the pelvis forward), in order to hold onto their ankles. This often has to do with the proportions of their torso, arm and leg lengths more than it does with their flexibility. When the pelvis is anteriorly tilted, the abdominal muscles (especially in the lower abdominal area in this instance) will not be actively working to support the torso. Instead, the hip flexor muscles will be shortened and possibly gripping to create and hold the position (depending on how much the hands are pulling as well). Additionally the extensor muscles of the back will also overactive to keep the body from continuing to hinge forward thanks to the pull of gravity. Counter the forward incline, we'll often see the chin lifted, indicating increased extension of the neck.
Here is the same dancer in a less obvious forward incline.
And where she is when she is holding onto her shins instead of her ankles and is able to be sitting upright with a more neutral pelvic position and her weight on her sits bones.
When we look at the body from the back we see a different set of adjustments.
One of the changes we see is the position of the scapulae (shoulder blades). When the dancer reaches her arms forward to grasp her ankles, her scapulae will protract - moving away from her spine and gliding slightly forward as the travel along the curved pathway of muscles laying atop the back of the ribcage. Since many tweens, teens and adults tend towards a shoulder line that is either protracted or rounded forward, this isn't a posture that is beneficial to encourage during warm up.
When her hands are allowed to move to where she can sit upright, we can see a better alignment of the shoulder girdle.
Starting in a neutral alignment is also beneficial to proprioception. Starting in a position where the body is aligned and balanced, allows the students to feel and begin to understand the forces that will take them off of balance or out of alignment.
Students will feel the changes in muscle tension which in turn either allows them to move into a stretching type movement or eccentric contraction; or if too extreme will trigger the stretch reflex where their body will tighten up to prevent injury.
Finding a starting place where the body is experiencing equilibrium will also teach the students the difference between active and passive positions. It is also important for them to learn that active positions have a wide range of magnitude - from a gentle and supportive activation to stronger engagement as the challenges are increased.
Passive positions rely on connective tissue structures such as joint capsules and ligaments to hold on to prevent injury. This type of movement is more apt to cause an injury than the more dynamic way of movement.
In addition to the purely physical reasons above, active positions require more mental connection between the brain and the body. The dancer needs to take self assessments about where his / her weight is, what they feel working or relaxed, if the magnitude of effort is appropriate for the movement etc. This leads to a more fully engaged dancer, more mindful practice and allows for more growth with less risk of injury.