Ground contact time balance: why symmetry improves running efficiency

If you want to improve running efficiency and become a faster runner: then pay attention to your running symmetry. That’s the findings of a recent study, published in the International Journal of Exercise Science.

In this article we’ll take a look at: running symmetry, why it’s important, how to assess it using ground contact time balance, and look at ways to improve run symmetry.

What is running symmetry? At the most basic level symmetry refers to something that’s the same, or equal, on both sides. If we, relate this to running, then the easiest way to think of symmetry is to apply force equally on the left and right sides of our body.

Why is running symmetry important?

Running symmetry is important for three main reasons:

  • Lower risk of injury
  • Improved running efficiency
  • Increases running speed

As you might expect, elite runners tend to have much greater symmetry than less well-trained runners. This is one of the reasons why elite runners tend to have greater efficiency; it also partly explains why they’re able to race at faster speeds and are less likely to suffer injuries.

In fact, a recent study (Joubert et al., 2020), looking at the effect of symmetry and running performance, found a clear link between imbalances (or asymmetry) and reduced running efficiency.

During the study, researchers assessed the relationship between ground contact time balance – a useful measure of running symmetry – and running economy. In this case, running economy was measured as the metabolic cost of running. And here’s the kicker – for every 1% increase in ground contact time imbalance, running economy decreased by ~3.7%.

Simply put, for every 1% of asymmetry the energy requirements of running increased by nearly 4%.

One interesting thing here: ground contact time balance is one of the easiest, and most accessible ways to assess running symmetry. If you have a Garmin device with a running dynamics heart rate strap, or pod, you can easily assess this yourself.

Let’s take a closer look at ground contact time and ground contact time balance.

What is ground contact time?

Simply put, ground contact time is a measure of the amount of time (in milliseconds) that your foot is in contact with the ground when running – from the initial foot strike to toe-off. It’s closely tied to running cadence and speed. And when either cadence or speed increases, we would expect to see a decrease in ground contact times.

Ground contact time is believed to be important for running efficiency; with faster ground contact times linked to improved efficiency. However, research in this area is mixed. And, whilst elite runners do have faster ground contact times, this is due in part to their faster running speeds. In fact, during the present study – ground contact time balance was far more predictive of running efficiency than ground contact time.

So, let’s take a look at ground contact time balance.

What is ground contact time balance?

Ground contact time balance compares the difference between the ground contact time on your left and right leg. To do this, the total ground contact time (for both legs), is split into a percentage for the left and right legs.

Essentially, this tells us how similar the ground contact time is between our left and right legs. Showing whether ground contact time is the same, quicker, or slower, on one leg, compared with the other. Through this, we get a measure of how balanced, or symmetrical, our running style is.

Why is this useful? As we’ve seen symmetry is important for running efficiency. It’s also a key player in long term injury risk.

Whilst, most runners have a slight difference in the ground contact time balance; at a certain point of imbalance, there’s an increased risk of injury.

With this in mind, it’s clear that a good level of symmetry is vital for both injury prevention and running performance.

Making sense of ground contact time balance

As I’ve mentioned, ground contact time balance measures the balance between our left and right leg. As an example 49.0-51.0 indicates that 49% of ground contact time is on left, and 51% on the right.

What does this mean? Simply put, a lower value indicates a faster ground contact time on that side. In some cases, this may be because one leg is more dominant, but it can also reflect biomechanical differences like leg length. Whatever the reason, it does tell us there’s a difference, an imbalance, or a level of asymmetry.

Clearly, the optimum level of symmetry would be an exact 50-50; however, in the real world this is rarely the case. 

So, what is a good level of symmetry? According to the Garmin website, a good ground contact balance should fall within the range of 49.3-50.7.

How Garmin rates the level of symmetry:

  • Poor symmetry (with faster GCT on right leg): Left > 52.2 / Right <47.8
  • Fair symmetry (with faster GCT on right leg ): Left 50.8-52.3 / Right 47.8-49.2
  • Good symmetry: Left 50.7-49.3 / Right 50.7-49.3
  • Fair symmetry (with faster GCT on left leg): Left 47.8-49.2 / Right 50.8-52.3
  • Poor symmetry (with faster GCT on left leg): Left < 47.8 / Right >52.3

An important point to consider – whilst a ground contact time balance in the range of 49.3-50.7 might seem fairly symmetric; it actually implies a 1.4% difference. And as we’ve seen, a 1% imbalance can lead to nearly a 4% increase in the metabolic cost of running.

What affects ground contact time balance?

Several factors can increase ground contact time imbalances, including:

  • Injuries – previous and existing injuries.
  • Muscle imbalances or weaknesses – especially in the legs, but also in the torso and arms.
  • Bio-mechanical differences – weakened arch on one foot, pelvic drop/rotation, or congenital differences such as leg length differences.

Other factors include running on a cambered surface, or, running around an athletics track.

Track running

Excessive running around an athletics track (especially if you’re right leg dominant), can lead to an increase (or worsening) of any imbalances.

So, why might track running make this worse for some runners? Track running in an anticlockwise direction, can cause a slight increase in the work rate of the outside (right) leg. Consequently, there will be a slight decrease in the ground contact time on the right leg. And, if your right leg is dominant, this can potentially lead to a worsening of any asymmetry.

Running terrain

In some cases, you may notice that running terrain (road, trail running, undulating, flat etc) may have an effect your symmetry. On Garmin’s website, they mention that “For many runners, ground contact time balance tends to deviate further from 50–50 when running up or down hills”. However, the effect that terrain has on GCTB is very individual. For me, running on undulating terrain tends to improve balance, particularly when trail running.

Running pace

Another factor to consider is the effect that running pace has. Often, symmetry can vary depending on running pace. As such, it’s important to assess this over a range of speeds to gain more of complete picture.

When I looked at my own GTC balance, there was clear variation depending on running speed:

  • At lower speeds GCT balance was very symmetrical ~50/50
  • During tempo, threshold and VO2max paces, there was a clear imbalance (~51-49 but sometimes as much as ~51.5-48.5) – with faster GCT on right leg.
  • Interestingly, this switched during faster (supra-maximal) intervals and hill sprints (~49-51) – this time with faster GCT on left leg.

Taken together this highlights the importance of including a range of different running speeds.

Addressing ground contact time imbalances

  • Seek treatment for any current, or previous injury, that may be affecting your running.
  • Include a range of different training speeds: easy, tempo/threshold training, vo2max and sprints.
  • Mix the terrain up – include undulating routes and trail running
  • Don’t overdo track running, or if possible attempt to include some running in the opposite direction.
  • Address muscle imbalances – using a combination of strength and core exercises, is an important first step. Not only can this help to improve symmetry, but this can help to protect against the risk of injury.

When it comes to addressing imbalances, unilateral exercises – single leg, or single arm exercises – work particularly well; after all, how are you going to correct an imbalance by working both sides at the same time.

Examples of good unilateral exercises for runners include: single leg squats, single leg deadlifts, lunges (forwards, backwards, walking lunges etc), step-ups, single leg glute bridges, side planks, single leg hopping, and single leg calf raises.

Reference:

Joubert DP, Guerra NA, Jones EJ, Knowles EG, Piper AD. Ground Contact Time Imbalances Strongly Related to Impaired Running Economy. Int J Exerc Sci. 2020;13(4):427-437. Published 2020 May 1.