An Introduction to Running Biomechanics

Biomechanics is one of those words that will either interest you or switch you off straight away.

There are many definitions as to what biomechanics means in the scientific community. But if we drop the fancy terminology and focus on how amazing the body is at movement and how it can help or hinder you in your sports performance – that is a good enough definition for this article.

The way we run is obviously different from the way we walk, and we are all unique. Our running styles are as diverse as our faces are, and like faces – some are prettier than others. Having a basic understanding of how we run can help you stay injury free, explain why you are currently injured and allow you to find the most efficient running style for you as an individual.

Your running style like your fitness can be improved, like any skill, but there isn’t one style that fits all. Improvement will depend on proper conditioning and active development, with the right coach. There are many different running styles like the Chi method, the Pose method, barefoot running, forefoot, midfoot and heel-to-toe running. Each is different and have different merits and problems. They certainly don’t suit everybody. For example, a forefoot running would struggle to run heel-to-toe and visa vera. Having a basic understanding of the biomechanics of running can help you appreciate your own running form and see where you may be able to make improvements. Working with a good coach is also a great idea as they can make sure your technique is correct and help guide you away from bad habits and overuse injury.

Although running most definitely depends on whole body interactions, dividing the running stride up into individual components or “phases” can help us understand how slight changes can help improve performance and reduce injury risk.

The running gait cycle

Let’s take a basic look at the running gait cycle. This cycle starts when one foot makes contact with the ground and ends when that same foot makes contact with the ground again. It can be divided up into two “phases” – the stance phase (during which the foot is in contact with the ground) and the swing phase (during which the foot is not in contact with the ground). The stance phase is the bit that practitioners pay more attention to, in the study of performance and injury as it is in this phase where the foot and leg bear the majority body weight and where injury risk is increased.

The swing phase is presented as a passive movement, i.e. the product of the stance phase and not consciously controlled.

Let’s take a closer look at the contact/stance phase of gait in greater detail

The Stance Phase

This can be divided into four stages: initial contact, braking (absorption), midstance, and propulsion.

1. Initial contact

Let’s imagine you are at that moment in your stride when both feet are off the floor (sometimes referred to as float phase). Your left leg is out in front of you and about to touch the ground. This moment (whether you land on heel, midfoot, or forefoot) is called initial contact and marks the beginning of the stance phase. Your right foot behind you is off the floor and in swing phase.

Forefoot runner.

2. Braking (absorption)

As soon as your left foot makes contact with the ground in front of you, your body is in effect performing a controlled landing or deceleration of your body mass. Your left knee and ankle flex (the opposite of straightening) and the left foot rolls in (pronates) to absorb impact forces.

Note: pronation is normal, in fact, excessive pronation can be healthy too for a few individuals. During this process of absorption, the tendons and connective tissue within the muscles store elastic energy (potential energy) for use later in the propulsion phase as kinetic energy.

3. Midstance

The braking phase above continues until the left leg is directly under the hips taking the maximum load (maximum risk of injury) as the body weight passes over it. The left ankle and knee are at maximum flexion angle. This moment is called midstance (you may also hear it referred to as single support phase). Ideally, this motion pattern needs to be smooth, controlled and decelerated otherwise injury risk is increased. Worn-out shoes, running on concrete and increased body weight etc. increase injury risk in this phase.

4. Propulsion

Now that your left leg has made a controlled landing and absorbed energy from the ground, it starts to propel you forward. This is achieved by your left ankle, knee and hip all extending (straightening) to push the body up and forwards, using the elastic/potential energy stored during the braking phase above. The more elastic energy available at this stage, the less your body has to use the muscles. The propulsion phase ends when the toe of your left foot (now behind you) leaves the ground, commonly referred to as “toe off” (TO). At this point, both of your feet are off the ground, so you are once again in the float phase.

Both feet off the ground is the ‘float phase’.

The Swing Phase

At the moment of toe off, your left leg has travelled as far back as its going to, and the heel starts to lift towards your backside. The height the heel reaches, and the returning drive of the knee is dependent on the power of hip extension achieved, and will hence be greater at higher speeds. This is when the kinetic energy takes effect pushing you through the air until gravity soon pulls you back down again.

Once the knee has passed under the hips, the lower leg extends (reduces the bend) in preparation once again for initial contact, marking the end of the swing phase.

Upper body and arm motion

Upper body motion and arm swing are as important as the lower limb gait cycle because without efficient torso and arm swing the legs cannot move efficiently. Zero arm motion will make the pelvis rotate too much, and legs move inefficiently. When the arms are moving efficiency from the shoulders (backwards and forwards), with the elbows at 90 degrees or less, this is an optimal running posture in the upper body for distance running. The faster the speed, the greater the arm motion is required to synchronised with the rapid movement of the legs.

The interaction between the upper and lower body plays a vital role in running. When they move well together it providing balance while promoting efficient movement. This balance is achieved by the arms and upper body effectively working in direct opposition to the legs. Bringing the left arm forward opposes the forward drive of the right leg and vice versa. During the propulsion stage (midstance to toe-off), the arms and upper body produce a braking force/moment.

By working as opposites, forward momentum is maintained. The arms and upper body also counterbalance rotation in the pelvis reducing the risk of lower back pain while running. The only thing that could upset this smooth metronomic motion is one leg longer than the other. This common natural asymmetry will create inefficiency and increase injury risk. If you suspect you have one leg longer than the other by while walking or running, then get it checked out by a sports podiatrist who specialises in biomechanics and gait analysis. You may actually require orthotics with a heel raise on one side to balance you out if the difference is found to be structural in origin.

Muscle action during the running gait 

  • Gluteus maximus and gluteus medius are both active at the beginning of the stance phase, and also at the end of the swing phase. When these muscles are weak, you will lose propulsion, and the pelvis may drop to one side while running.
  • Tensor fasciae latae is active from the beginning of stance, and also the end of swing phase. It is also active between early and mid-swing. Weakness in TFL can result in iliotibial band friction syndrome and lateral (outer side) knee pain. It can also cause greater trochanteric bursitis
  • Adductor Magnus is active for about 25% of the cycle, from late stance to early part of swing phase. One leg longer than the other can create pain and stiffness in Adductor Magnus.
  • Iliopsoas activity occurs during the swing phase for 35-60% of the cycle. Weak hip flexors or asymmetry in flexion and extension of the leg can create pain in the hip flexors.
  • Quadriceps works eccentrically for the initial 10% of the stance phase. Its role is to control knee flexion as the knee goes through rapid flexion. It stops being active after the first part of the stance phase, there is then no activity until the last 20% of swing phase. At this point, it becomes concentric in behaviour, so it can extend the knee to prepare for heel strike. Weak quads can cause ‘Runners knee syndrome’ – also known as patellofemoral pain syndrome.
  • Medial Hamstrings become active at the beginning of the stance phase (18-28% of stance), they are also active throughout much of the swing phase (40-58% of initial swing then the last 20% of swing). They act to extend the hip and control the knee through concentric contraction in late swing, the hamstrings work eccentrically to control knee extension and take the hip into extension again. Both anterior (forward) and posterior (backward) pelvic rotation and create tissue stress and injury in the hamstrings. Pelvic rotation can be due to adaptation to leg length inequality.
  • Gastrocnemius muscle activity starts just after loading at heel strike, remaining active up until 15% of the gait cycle ( this is where its activity begins in walking). It then re-starts its action in the last 15% of the swing phase. The calves (gastrosoleal complex) is often injury with either delayed but especially early heel-lift created by having one leg longer than the other.
  • Tibialis anterior muscle is active through both stance and swing phases during running. It is active for about 73% of the cycle (compared to 54% when walking). The swing phase when running, is 62% of the total gait cycle, compared to 40% when walking, so TA is considerably more active when running. Its activity is mainly concentric or isometric, enabling the foot to clear the support surface during the swing phase of the running gait. Weak quads can cause increased knee flexion, and the knee rides forwards because delayed heel-lift. In this functional position tibialis, anterior can become hypertonic (spasm) and be extremely painful especially while walking and running on concrete.