Gait and Running Biomechanics

There is a particular biomechanical pattern our bodies should follow with each and every step we take, however this does not always occur, leading to potential injury (acute or cumulative).
2 phases of gait:
1. Stance
2. Swing
Which do you think is longer? Stance or swing?
FUN FACT: the stance phase = 0.6 sec, the swing phase = 0.4 sec, therefore making the stance phase longer
The stance phase has 3 main components:
1. Contact: 0-27% of gait cycle (heel strike to full forefoot load)
2. Midstance: 27-67% of gait cycle (“vaulting” motion of the body over the stance foot
3. Propulsion: 67-100% of gait cycle (heel lift to no more foot contact)
i.e. the longest phase is the midstance phase during walking.
The running cycle has the same phases, but because running consists of the “need for speed” and more force (to propel the body forward), the phases are altered in terms of their timing.
1. Contact: 0-20% of gait cycle
2. Midstance: 20-45% of gait cycle
3. Propulsion: 45-100% of gait cycle
As you can see here we have a decreased contact and midstance phase and an increased propulsion phase.
FUN FACT: we are born, reflexively knowing how to do the “swing phase” of gait, but it is the “stance phase” that is a learned behavior.
FUN FACT: it takes approx. 10 years for humans to become efficient at being bipedals!
In order to be effective walkers, and even moreso effective runners, our body must learn the path of least resistance. We want to “…effectively decrease angular displacement of the body’s center of mass.” i.e. if we have a centre of mass we don’t want to deter too much away from this.
This requires a multitude of things occurring in synergy thereby increasing efficiency.
1. Pelvic rotation: adequate rotation is necessary to reduce the amount of hip flexion and extension while still keeping the same stride length.
2. Pelvic tilt: “Eccentric contraction of the hip abductors during midstance lowers the pelvis on the side of the swing leg…" Our hip abductors consist of 4 main muscles: gluteus maximus (your largest glute muscle, medius/minimus and TFL.
3. Knee flexion/extension during stance phase: early stance calls for knee flexion, late stance calls for knee extension
4. Hip-knee-ankle interactions:
A. Stance Contact = Eccentric contraction of anterior (front) muscles, bending of the knee
B. Stance Propulsion = plantarflexion (pointing) of the toes
C. Swing = flexion of both the hip and the knee (without this you would à hip circumduction à inefficiency)
5. Lateral pelvic displacement: support leg adducts, swing leg abducts. Luckily we have slight genu valgum which keeps the tibia (shin bone) relatively straight during gait, and causes less required lateral deviation to maintain balance à less strain on the hip abductors and fibularis group than would otherwise be required.
To be efficient runners, a higher degree of hip and knee flexion is required as opposed to general gait (which calls for more stiffness/inflexibility of the lower limbs).
Why? To reduce shock!
Just like the 3 little bears, we want ranges of motion in the joints that are “just right.” Too much range of motion causes potential injury because of the amount of effort required to restrain the body from this excess mobility, but not enough range of motion is detrimental also, as a lack of range of motion causes other tissues to compensate for the ones that aren’t working optimally.
1. HIP
Even during walking, the hip must have at least 15-20 deg of rotation, 30 deg of flexion and 10 deg of extension.
Runners often succumb to reduced hip extension, especially those that have consistent desk jobs, as sitting all day creates tightness in the hip flexors. One of our major hip flexors is called iliopsoas (show picture and describe location) This muscle attaches to the leg bone and can not only cause a lack of blood flow in the veins around the femoral head (which can contribute to hip pain), but can also affect the labrum of the hip if it is too tight resulting in potential labral tears, or back related issues. Running requires even more hip extension than walking, so having a proper amount is imperative
2. THE KNEE (also known as the tibiofemoral joint)
must have at least 180 deg of extension and at least 50 deg of flexion for walking.
Without proper knee extension, strain through the deep leg muscles and the ankle are strained (ankle has to dorsiflex more)
Without proper knee flexion the leg has to circumduct in order to clear the ground à excessive forces on the other sided calves, glutes and same sided low back muscle and hip flexors. Having full knee flexion during walking has been coined the most important determinant, as the metabolic cost to the body not having this is huge.
3. THE ANKLE
must dorsiflex (which is the motion of bringing the toes up towards the nose) at least 10 deg
Runners require more hip extension, but with this increased hip extension increased ankle dorsiflexion is also required. Without proper dorsiflexion there is too much pronation of the ankle à contracture of the Achilles à collapse of the medial longitudinal arch à potential injury to the front of the foot (forefoot). Some of these potential injuries include metatarsal stress fractures, impingement exostosis (where extra bone growth forms as a protective mechanism, but is actually counter-protective and causing pinching of certain tissues in the ankle), metatarsalgia, plantar fasciitis, hallux valgus, and midfoot sprains.
It is important to note that one key factor relating to a lack of ankle dorsiflexion leads to the injuries just mentioned is tightness in the gastrocnemius muscle (which is your most superficial calf muscle)
4. THE SUBTALAR JOINT
must pronate at least 4 deg from neutral
Why? To absorb shock
Not enough ROM in this joint can à too much plantarflexion (pointing of the toes) -> strain on the front shin musculature, potential acquired plantarflexion of the first toe, and knee injury.
If there is not enough subtalar pronation, the knee goes into a valgus position compressing the outer aspect of the knee.
Those with limited motion of the subtalar joint may widen their gait. Though this may help the knees, it is hard of the glutes and outside shin musculature (fibularis group) and is also less efficient for the body, because it changes the centre of mass and even affects the arms! (they abduct more)
Other injuries arising from a lack of subtalar motion are neuritis (inflammation of the nerves in the foot), and stress fracture of the lesser metatarsals. Without the proper subtalar motion the foot cannot evert. Usually push off in gait happens between the 1/2nd metatarsals, but without proper eversion you push off on the lesser metatarsals leading to these potential injuries.
5. Lastly, THE 1st MTP
has to dorsiflex at least 40-55 deg for gait, for running it’s desirable to have 65 deg to prevent injury because as you run the stride is longer and requires more extension of the big toe.
In those that pronate, as opposed to having a neutral foot, they need more dorsiflexion of the big toe, because they push off from gait closer to that toe as opposed to in between the 1/2nd which is more desirable. Therfore, if you know you are a pronator, you will have to work extra hard at getting proper dorsiflexion of the big toe in order to remain injury free! Of course it is best to try and fix your pronation through proper awareness and education, rehab and potentially orthotics, as well as training the sufficient dorsiflexion required.
So these people have to make sure that they have good ankle mobility (i.e. at least 15 deg of ankle dorsiflexion