Want to control gravity on skis? Here’s how
September 8, 2015
Big trees fall hard.
It's an old saying that actually has roots in the world of human biomechanics. And, it makes sense — a 100-foot redwood will fall hard, just like a 7-foot NBA basketball player will if his ankle is tripped.
It's relative, of course, but gravity is constant: 9.8 meters per second squared (m/s2). So, we deal with gravity every day, and, as an athlete, the full effects of gravity can be thoroughly enjoyed. A few examples of "gravity sports" include skiing, mountain biking and longboarding. Usually, high speeds and G-forces (the effects of gravity) draw people to these sports.
Let's dig in a bit deeper to understand how body positioning and relative height directly impact our safety and performance on this gravity-laden planet.
The base and center
Rewind years ago to when you first started standing and walking as an infant. It was difficult to get your bearings with gravity — the effects were literally weighing you down.
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So, the human body has innate responses to get us upright and keep us there. As we start to learn standing stability, our feet are wide and our stance is low. This is our base of support. The first steps we take are typically wide shuffles, with our arms held high to help with balance.
As we grow older and develop core strength, our walking efficiency improves, and we adopt a narrower gait, holding our arms at the sides. With time and nourishment, we grow in both height and width. The bulk of our body weight is called the center of mass. As we get taller, this gets farther away from the ground — one reason why it hurts more to fall when we get older.
The athletic stance
Sports and everyday recreation play with the delicate relationship between your base of support and center of mass. We adopt an "athletic stance" to increase stability and improve performance while in play. This position is similar to the most stable positioning we found as an infant: It involves a wide base, a crouched stance (knees flexed) and a forward-leaning trunk. Collectively, these moves bring your center lower and increase the stability of your platform.
It's a move that we automatically revert to quite often as a safety mechanism. For example, the "tuck" while skiing straight down a slope is for aerodynamics, but it also increases your stability.
On the opposite side is the dreaded back-seat position. It can sneak up on you and take you right out of the driver seat. From a biomechanical perspective, this happens when your center of mass gets behind your base of support (i.e. your trunk and body weight are behind your feet). This situation is never fun and can be quite dangerous for your knees.
In mountain biking, the balance between your base and center is just as delicate. With a dropper seat-post, a rider can remotely drop the seat to have more room and crouch lower. This lowers the center of mass, which gives more stability through rough terrain and on steep descents. Along with a dropper, skilled riders will widen their elbow and knee positioning to improve bike control and overall stability.
Is height your enemy in gravity sports? Tall and big-bodied athletes are not destined to be awkward and unstable. Anyone, of any shape and size, can fall and learn lessons the hard way about working with — or against — the big G (aka gravity).
Whether you are downhill mountain biking, skiing, riding, longboarding or getting rowdy with some other gravity sport, use your athletic stance: Get low, find a stable base, center your body and activate that core!
Eric Dube is a licensed physical therapist and orthopedic clinical specialist with Howard Head Sports Medicine in Summit County.
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