Foot Strike & Functional Movement: Part 1

Whether you are a Physical Therapist, Strength Coach or Personal Trainer, the most powerful tool you have is your ability to assess human movement. From the overhead squat to the step up, each of us probably has our favorite, or go-to, assessment techniques we perform on all patients or clients. 

As we consider the most appropriate assessment techniques for demonstrating instability or compensation patterns, how much do we consider function?

As we look closer at the movement assessments that we perform daily, I challenge you to consider how each assessment transfers to the most functional movements that your clients do every day. One such movement that your client is doing up to 8,000 times a day is walking! 

Learning Objectives: 

1. To build an appreciation for the role a walking gait assessment has as a form of functional movement assessment
2. To understand the basics to the human gait cycle and the functional demands at each phase of gait
3. To emphasize the concept of efficiency and how the body loads and unloads impact forces through body spiraling 

Functional Demands of Walking

The average adult takes between 5,000 and 8,000 steps per day, with each step requiring us to load and unload 1 – 1.5 times our weight in ground reaction forces. Not only does this repetitive loading and unloading of impact forces require proper mobility and stability – but it requires this movement pattern to occur efficiently while standing on one leg!

The functional demands of walking include 1) deceleration or loading of impact forces, 2) balance and 3) acceleration or unloading of impact forces. This ability to load, store and release kinetic energy truly is the foundation to all functional movement, not just walking.

One movement assessment that I perform more than any other technique is the walking gait assessment. Why I choose this assessment is because the walking gait assessment will demonstrate the client’s ability to:

• load and unload impact forces (efficiency)
• maintain dynamic single leg stability (balance)
• integrate joint coupling (kinematics)

Part 1 of this two-part article series will focus on the basics to the human gait cycle and the functional demands that are placed with each repetitive step often amounting to over 8,000 times a day, while Part 2 will focus on how to properly perform a walking gait assessment and design programming based on your observations.

The Human Gait Cycle

The human gait cycle is broken down into two primary phases: Stance Phase and Swing Phase. We spend a majority of our time in Stance Phase (60 percent) and 40 percent of our time in Swing Phase.  

If we consider that most injuries we see are overuse-related, this would mean that a majority of our injuries are occurring during Stance Phase – or when we are in contact with the ground. Because of this, this two-part article is going to focus on the Stance Phase of gait.

Stance Phase can be broken down into five additional phases: Initial Contact, Loading Response, Midstance, Late Midstance and Propulsion

When assessing a client’s gait it’s important to understand what occurs at each phase of gait and as well as joint alignment needed for proper stability, transfer of forces and movement efficiency. 

Initial Foot Contact

The gait cycle begins with foot strike or initial foot contact. In human walking, the initial foot contact point is the heel – or more specifically the outside of the heel. Have you ever wondered why we strike the ground on the outside of our heel?

The answer to this question lies in foot mechanics and how the body loads impact forces. 

When we say foot mechanics, I want you to focus primarily on the subtalar joint (STJ) position. The STJ is the foot joint found in the rearfoot and is formed by the talus above and the calcaneus below. With every step we take the STJ moves through inversion and eversion in the frontal plane.

                      Eversion                                                                  Inversion

An inverted STJ position is equivalent to a stable, rigid and locked foot, while an everted foot is equivalent to an unstable, flexible and unlocked foot. The stability provided by an inverted foot is the first of two reasons why initial foot contact is on the outside of the heel. 

The second reason why we strike the ground in an inverted foot position has to do with joint coupling. When we say joint coupling, we mean how the movement of one joint influences a neighboring joint. When we look at the joint coupling associated among the foot, knees, hip and pelvis, it is the STJ that interconnects the foot with the rest of the lower extremity.

If you were to stand up now and move your feet through inversion and eversion you should feel that there is a coupled motion that is occurring in your knees and hips. The joint coupling that is occurring with STJ inversion is tibial and femoral external rotation in the transverse plane and a posterior tilt of the pelvis in the sagittal plane. Conversely, the joint coupling that occurs with STJ eversion is tibial and femoral internal rotation in the transverse plane and an anterior pelvic tilt in the sagittal plane. 

Now how does this relate to the loading response that occurs during gait?

When we think about how the body loads impact forces or softens a landing, we typically think about joint flexion.  Well another part of this joint coupling described above occurs with joint flexion. This means that when our hips are flexing in the sagittal plane they are also internally rotating in the transverse plane. Likewise when our knees are flexing in the sagittal plane, our tibia is internally rotating. So if we think about joint loading through knee & hip flexion, we are also loading through femoral and tibial internal rotation and STJ eversion. 

Therefore the second reason why we strike the outside of our heel during initial foot contact is this allows are STJ to move into eversion and our lower extremity to internally rotate so that we can absorb shock and load impact forces. This STJ eversion and tibial / femoral internal rotation is also known as a body spirals. 

Deceleration Phase

The control of the loading response or this deceleration phase is through eccentric muscle contractions. Any weakness in eccentric endurance will result in movement dysfunction or an increased risk of injury. 

When we are assessing a client’s walking gait cycle we can observe their ability to decelerate eccentrically and how efficiently they are able to load impact forces. Any weakness in eccentric control either in the feet or hips will present as foot pronation, knee valgus or excessive hip internal rotation. More to come on this shortly!

Single Leg Stability

Immediately after initial foot contact our opposite leg begins to leave the ground requiring us to shift our body weight into a single-leg stance. Peak single-leg stability occurs during the midstance phase of gait. Midstance is also the phase of gait when we are in our peak body spiral or peak deceleration. This means that this is also the phase of gait where improper joint alignment is often observed.

Proper joint alignment in midstance requires triplantar stability of the lower extremity. We will want to note pelvic stability in the frontal plane, knee stability in the transverse plane, and foot stability in the frontal plane.  

As soon as peak deceleration is reached in midstance, the body begins to prepare for propulsion - or the release of this previously loaded spiral - by shifting into foot inversion and the tibia and femur into external rotation.

Peak Potential Energy

As the body begins to prepare for propulsion one last critical step must occur to achieve peak potential energy – this occurs in late midstance. Late midstance is characterized by us passing over our ankle joint to get maximum stretch of our Achilles tendon. Since most of our elastic potential lies within the Achilles tendon, any client that bypasses this step due to limited ankle mobility or tight calves will not achieve their peak potential energy and movement efficiency will be compromised.

Since many people lack adequate ankle joint mobility, this is another point in gait where we will observe many characteristic compensation mechanisms including early heel lift, pronatory twist or foot abduction. 

Elastic Energy Recoil

After moving through late midstance and achieving peak potential energy, it is time to release this potential energy and propulse the body forward into our next step. As we begin to shift forward over the foot and rock over our digits, joint coupling again becomes an important feature of this elastic energy recoil. 

As we dorsiflex our digits and plantarflex our ankle the STJ is driven into an inverted position. This return to STJ inversion during propulsion is again two-fold. First reason is that we want to push off of a rigid foot and second reason is STJ inversion is coupled with tibial and femoral external rotation which drives the knee and hip into extension, propelling the body forward. If our client is not able to transfer this energy through this body spiral, the client will not be moving efficiently. 

Swing Phase

Although this article is primarily focusing on the functional demands of stance phase, it is still important to understand a few basics of Swing Phase. Swing Phase can be broken down into Initial Swing, Mid-Swing and Terminal Swing. 

Initial Swing is the period characterized by the elastic recoil of our stored potential energy. No true concentric activation is occurring until the swing leg is directly under the torso. As the swing leg begins to approach Mid-Swing, the first hip flexor to engage is the adductor longus. This is an important detail as those clients who enter Swing Phase too early are at risk of an adductor overuse injury or adductor strain. As the swing leg begins to enter Terminal Swing, eccentric contractions kick in again to control deceleration before Initial Contact. 

Summary

The above article gives a brief summary of the functional demands of walking. Demands that require timed muscle activation patterns to efficient load and unload the impact forces with each step that we take. Any delay in the timing of these muscle activation patterns and compensation sets in as well as the increased risk of injury. 

Part 2 of this series will focus on the basics of performing a gait assessment and how to design programming to improve client efficiency and movement patterns during the walking gait cycle.