Throwing this out for your consideration and thoughts...
by: bud heishman
Our feet are the beginning of the kinetic chain and our most sensitive proprioceptors for balancing. The foot/ankle can move in three planes of motion, each relating directly to one of the PSIA skiing skills. We can dorsiflex and plantar flex (pressure), we can evert and invert (edging), and we can abduct and adduct (rotary). (note: pronation is a combination of dorsiflexion, eversion, and abduction and supination the opposite) Though our ski boots fit snugly around our feet, all these planes of motion are available to some degree inside our boots and use the resistance from the boot liner and shell to transmit impulse to the skis. The following will isolate each range of motion and it’s role in skiing, then try to put them all together in concert.
Dorsi flexion/Plantar flexion:
Standing in your boots and skis in a cuff neutral stance, simply dorsiflex (pull forefoot upward to close ankle joint) inside your boots. What happens? Do your hips move forward or back? Does the pressure increase or decrease under your heels? What muscle(s) do you feel firing? The anterior tibialus muscle, which contracts during dorsiflexion, is one of the most important muscles in skiing in this author’s opinion.
Now plantar flex (press forefoot downward to open ankle joint) and notice what happens? Though many times while skiing, we will forcefully dorsiflex to pull our mass forward, we should generally use plantar flexion in a more passive manner or a relaxation of the ankle rather than an active pressing and is generally most effectively used to modulate our fore/aft balance before the fall line.
Now think about this range of movement while making some shorter radius slow turns, more pivoty at first. As you enter the finish phase of your turn and begin the edge change, simultaneously dorsiflex your feet by pulling your toes upward, then as you move to the new edges, immediately allow your ankles to plantar flex to begin the new turn as the path of your cg. and skis begin to diverge. To make this even more dramatic loosen your top two boot buckles, keeping your power strap snug. Play with this movement as you begin to shape the turns and move toward a medium radius turn with more edge angle to feel the fore/aft affects of using this foot and ankle movement. You will begin to feel the pressure under your feet move from ball to arch to heel throughout the turn but note this should be a result of the movement of your ankles inside the boot rather than a deliberate fore/aft pushing or pulling of your feet or a fore/aft movement of your hips, which should remain relatively quiet over your base of support.
Our foot and ankle movements should facilitate keeping the line between our base of support and cg. in line (balance axis) with the resultant force throughout our turns which will entails balancing with accelerations and against de-accelerations of each turn.
Notice that dorsiflexing your ankle will pull your hips forward into transition and plantar flexing will keep the shovels engaged with the snow as the paths of your skis and cg. diverge toward apex.
Now let’s play with the lateral movements of the foot and ankle. When making parallel turns one foot is everting while the other is inverting (tipping). We can feel this inside our boots standing on the flat by simply tipping the feet inside our boots. Moving from little toe edge to big toe edge feel the muscles in the feet tensing to tip. Feel when the foot is everted (tipped to the inside edge) the inside ankle bone press against the boot hinge creating a kind of pressure triangle between the first met head, medial ankle bone, and the heel. As the foot is inverted (tipped to the outside edge) we can feel the outside ankle pressing against the boot hinge. These movements serve to adjust initial edge angles and make fine tune balancing adjustment throughout our turns. While skiing in a well balanced stance these foot and ankle movements inside the boot are invisible to the observer but are very important to dynamic balance.
Let’s make some turns now isolating these tipping movements by skiing down a flatter slope in railroad track turns, initiating the edge change with feet and ankles. Begin in a static position and simply tip on as high an edge as possible to one side then the other using counter balancing efforts up the body. How high can you tip and still balance? Now take it into motion and simply tip from one set of edges to the other without any effort to turn the feet. Progressively ski the railroad tracks into medium radius high edge angle dynamic turns still emphasizing the tipping movements in the ankle. Note: leading the transition with the first movement being the tipping to the little toe edge of the downhill ski will pull us into the new turn with a simultaneous edge change eliminating any sequential edge change.
Here we discover the foot and ankle movements of inversion/eversion are biomechanically linked to the movements of adduction/abduction. In your bare feet you can experiment with this by twisting your foot inward (adduction) you will notice the foot also tips to the little toe side (inversion) and conversely, twisting the foot outward (abduction) you will notice the foot also tips to the big toe side (eversion). This linked movement plays and important part in carving turns we will discuss shortly.
Let’s begin playing with Ab/adduction by making pivot slip turns to feel the feet twisting inside the boots. Granted other rotary movements are involved here, notably the femurs rotating in the hip sockets and the tib/fib rotating under the knee joint but the movement here should initiate in the feet for this task and should all occur with the hips and shoulders stable to anchor the lower leg movements.
You will notice as we ski from the pivot end of the spectrum in linked pivot slips, toward the carving end of the spectrum, the role of the foot movements change a bit. In a pivot slip with momentum moving straight down the fall line the tips are released and pivoted into the fall line and then pivoted across in the opposite direction. As we progress toward the carving end of the spectrum by adding more edge angle and/or forward pressure our momentum is directed more forward closer to the direction the skis are pointing, we begin to see how the twisting of our feet and the tipping roles change. In the pivot slip we twist our feet into the fall line and resist tipping them. Conversely, when carving turns we tip our feet, and consequently because the movements are biomechanically linked, twist our feet in the OPPOSITE direction of the turn direction (or resist the twist into the turn direction)! I call this the “Tip n Twist” because we twist one
way and tip the opposite which as we discovered, are biomechanically inseparable movements in our ankles. By understanding and using these linked movements, we can improve our carving turn entries. (note: the tips do not go in first in a carved turn, our bodies do! Conversely while in a pivoted turn entry our tips do go in first). This is a movement spectrum which is poorly understood by many yet is worth exploring.
Now that we have isolated each movement of the foot and ankle, let’s put it all together in some turns to optimize the benefits of each plane of motion. It is probably easier to first play with these movements making “air turns” with our hands to simulate the blends of fore/aft, lateral, and rotary movements with our feet, then visualize how they will feel inside our boots before trying on skis. You may look like a Polynesian Hula dancer with your hand movements while practicing this? Visualize, from your edge change into a carved right handed turn, plantar flexing while simultaneously twisting your feet to the LEFT and tipping them to the RIGHT (remember we can not separate these two planes of motion). As you arc around the turn through the fall line and into completion your ankles begin to dorsiflex, pulling the Cg’s release toward the new turn apex, and simultaneously rolling the feet and ankles toward edge change. This may sound like a complex movement being described here, however; The actual movements inside the boots are very simple once you grasp the sensations.
How does this movement pattern change if I am making a sub-planing (windsurf analogy) or non carved turn? The mechanics change a bit as referenced above when we are skiing closer to the pivot slip end of the carving/pivoting spectrum (see graph ATM Teaching Concepts III). Here, beginning at edge change, assuming we are in a good body position balanced over the downhill ski and slightly countered, the movements in the feet and ankles are more subdued as we release our edges the tips seek the fall line aided by twisting our feet, this time, into the turn direction with the new edge engagement (tipping) occurring much later in the turn around the fall line. Here the tips DO go in first vs. in a planing or carved turn where the Cg goes in first. The more we migrate toward the extremes of the carve/pivot spectrum, the more evident this becomes and a movement blend occurs along the continuum in between. The blend then is directly related to where our momentum is directed and how much momentum we have.
By understanding and effectively using these foot and ankle movements, your skiing accuracy and balance will improve! Think with your feet and have fun!
Edited by bud heishman - 2/27/11 at 4:00pm