Slant Boards
Elevating an aspect of the foot during movement alters how forces are produced. The heel tends to be the element elevated during activities like squats, particularly with individuals that have a difficult time reaching adequate depth. Toes can also be elevated, with the common intention of improving ankle dorsiflexion and placing greater demand on the posterior anatomy. Although there is quite a bit of complicated rationale for these tools, the mechanics at play may be based on a simple, well-established rule.
Newton’s third law of motion describes how objects exert forces on each other that are equal and opposite. If I elevate the heels for a client in order to improve squat mechanics, what I am actually doing is pushing them upward and forward via the slant board. Their immediate response is to push back against the board with the same degree of force, meaning backward and down. That simple change in position, altering the forces, may be the more influential piece at play than simply ankle range of motion or any other specific joint. The entire system reorganizes to allow for a better ability to sit down into the squat.
Let’s look at the ankle in more depth, keeping in mind that the entire system behaves the same way with the same mechanics. If heels are flat and we ask someone with limited mobility to squat, we tend to see their heels come off the ground as they descend beyond their capabilities to dorsiflex. Their center of gravity is sliding forward too quickly as they come onto their toes. Elevate the heels on a board and their immediate response is to shift backward to prevent falling forward. That response puts slack on the calf musculature and allows for those muscles to actively slow the forward movement of the tibia and a deeper descent in the squat. This pattern is present at the pelvis, thorax and onward making it plausible for the entire system to achieve a more upright position during the squat.
If we reverse the slant board, elevate the toes we get a similar response but in the opposite direction. We now feel like we are being pushed back due to the ramp, our reaction is to push forward, equally. This shortens musculature on our back side, propelling us forward faster and to a higher degree. This may be a preferred position pending the intention of the exercise.
Slant boards can be a valuable tool when looking to improve client or patient performance. The angles we use and direction of application has massive influences on mechanics. Elevate the heels and slow the center of gravity, if the toes get elevated we are hitting the accelerator. Both can be useful strategies, but the context determines which activity is most appropriate for the person in front of us.
Austin Ulrich, Physical Therapist
