Gravity can be defined as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped. In the context of yoga, gravity provides the medium in which we can exert force, generate strength, and root against to form poses. By understanding the basic principle of ‘lines’ of gravity, we can be more effective in our approach to alignment, exertion, and pose formation.
Mountain Pose is a great example to begin with – in simple standing posture, we can feel the lines of gravity going vertically down through the crown, spine, and feet. If we take the same mountain pose position and turn it horizontally (ie on our belly), we feel the lines completely different: coming from the back body through to the front body. When comparing both positions, the body is technically in the same alignment form, but this simple change in orientation creates a different effect with gravity.
Taking this concept a bit deeper comparing Cobra versus Upward Facing Dog pose. In Cobra pose, the aim of the posture is to generate a back arch utilizing primarily the back extensors and some secondary assistance from the arms (depending on one’s approach and level of flexibility in the spine). The back extensors and tricep muscles engage exerting against the vertical line of gravity. The abdominal muscles engage as well, but as a protective mechanism for the lower spine (pelvic tilt to avoid lumbar compression).
Now, how about Upward Facing Dog. We could assume since the spine/torso are in a relatively similar back arch as Cobra that the same muscle groups are engaging in the same manner – that assumption would be wrong even though the lines of gravity are the same. By elevating this back arch (only hands and feet now on the floor), we no longer have the back extensors muscles contracting to work against gravity – they now settle in with the line of gravity. Instead, the abdominal muscles become the primary muscles in the torso working against gravity – the rectus abdominus engages to prevent the spine from fully collapsing with gravity. The arm and shoulder girdle muscles are working to elevate and stabilize the upper body. The front thigh and shin muscles fire to elevate and stabilize the lower body.
So, in this comparison of back arches, we simply modified the body’s position in space (grounded versus elevated) to dramatically change what muscles are primarily being used throughout the core to form the back arch. Why is this concept important? If as a teacher, I need to design practices with specific conditioning needs/intentions, I need to understand and appreciate force load principles as a first priority. I could incorrectly assume that I could use Upward Facing Dog pose as a ‘back strengthening’ asana since it forms a back arch in the same spacial position as Cobra pose. If my intention were strengthen the back, I would utilize Cobra pose or variations of locus pose instead. This becomes even more complex when we were start to apply changes in lever length against gravity (ie: keeping arms at your sides versus extended forward in locus pose).
To understand the basic relationships of gravity and yoga postures, simply start in Mountain Pose and play around. Very slowly change your plane of spinal position – for example, go from Tree Pose to Warrior 3 balance. Feel the change of muscle engagement throughout the body (but with particular attention on the spine) just by manipulating were the body lies in the flow of gravitational forces.
As yoga teachers, these concepts become increasingly more relative as we work with people of varying experience levels. How do we manipulate body positions against gravity to decrease or increase exertion, thus meeting the needs of our students. Why do modifications like put knees on the ground in plank dramatically change the exertion level of asanas? If we are going to place students’ bodies in asana formations, understanding gravity and force principles should be one of our primary teaching foundations. We don’t need to attend physic classes to fully grasp these concepts, but to simply play within our personal practice and become fully aware as we move, align, and manipulate within space.