The best runners know that symmetry is important. When you apply force evenly on the left and right sides of your body, you will become more efficient–and faster–Runner. More importantly, you are less prone to injury.
Ground Contact Time (GCT) balance is a metric that can help improve your running symmetry.
Get to grips with ground contact time balance in this article and read our five tips for improving running symmetry.
What is the ground contact time?
Understand ground contact time balance, let’s start with the ground contact time, GCT for short. This is the time your foot is in contact with the ground while running. For most runners, a GCT between 200 and 300 milliseconds is normal. Elite distance runners are able to achieve ground contact times of less than 200 ms.
The amount of ground contact in your walkway is also known as the stance phase. The stance phase begins with the first kick, continues through the “supporting” middle class and ends with lifting the toe.
Why is the ground contact time important?
Running speed depends on the ability to quickly exert force through the ground. The faster you can apply force through the floor, the faster you will be propelled forward.
Scientists have been studying the relationship between ground contact time and running speed for decades. But until recently, GCT was an inaccessible metric reserved for biomechanics in a laboratory.
Biofeedback and Wearable Technology
Portable fitness equipment have revolutionized fitness training and how we measure our performance. Trackers and accelerometers now provide accurate, real-time biofeedback for runners everywhere. And they work.
A 2020 study was the first to examine the effects of wearable device biofeedback on running biomechanics.  The results were positive. The observation of the GCT biofeedback reduced the vertical displacement (hopping) and the running time of the runners and increased the knee flexion – key factors for performance and injury prevention.
That brings us to the next evolution in biofeedback: GCT balance.
What is the ground contact time balance?
Ground contact time balance is a measure of how similar the ground contact times of your left and right legs are. The GCT balance is usually shown as a percentage split. A 50/50 split is the theoretical optimum and indicates an equal GCT for both legs. In reality, the GCT balance is rarely 50/50. Anything between 49% and 51% is considered fairly symmetrical. However, if your GCT balance is above 49/51 (an imbalance greater than 2%), the asymmetry can affect your performance and put you at risk of injury.
Ground contact time balance is a measure of how similar the ground contact times of your left and right legs are.
The GCT balance is usually shown as a percentage split. A 50/50 split is the theoretical optimum and indicates an equal GCT for both legs.
In reality, the GCT balance is rarely 50/50. Anything between 49% and 51% is considered fairly symmetrical. However, if your GCT balance is above 49/51 (an imbalance greater than 2%), the asymmetry can affect your performance and put you at risk of injury.
Why is the balance of ground contact time important?
Some fitness tracker functions are little more than gadgets (e.g. oxygen Saturation) . so what does GCT Balance do it differently?
GCT balance is important because symmetry is important. Elite athletes have a high degree of symmetry, and the fastest runners are the symmetrisch. 
Asymmetry, on the other hand, is metabolically and biomechanically inefficient. This is because one side of your body is working harder to compensate for the other.
For efficient forward movement, the front-to-back (sagittal) movement is most effective. When there is an imbalance, energy is wasted moving your body in the frontal plane (think of hip adduction) or transverse plane (think of trunk rotation) to counteract the asymmetry.
For example, if one leg is weaker or less flexible, we tend to compensate for this with excessive arm swing or torso rotation.
What science says about the GCT balance sheet
The International Journal of Exercise Science published research on the effects of GCT imbalance on running economics last year. 
Notably, the study showed that running economy was reduced by almost 4% for every 1% imbalance in the GCT.
For comparison: with a GCT score of 49/51 (with one leg only 2% longer on the ground than the other), the energy requirement for running at the same speed is 7.4% higher.
For a 70 kg runner at 15 km / h this would increase oxygen consumption by ~ 4 ml.kg.min. That’s a big part of your V̇O2 Max.
It is unclear to science how asymmetry causes injury.  Anecdotally, however, it’s likely that any weakness on one side puts additional strain on other muscles and joints, putting you at risk of further injury. 
In short, balancing the time you spend on each foot is important to prevent injury and improve economy and performance.
Here are 5 tips for improving running symmetry and ground contact time balance
1. Identify the asymmetry
Use the GCT balance metric to find out which leg is slower. The leg with the higher GCT balance percentage (> 50) spends more time in contact with the ground. The slower leg is the one that is being worked on.
Test the asymmetry by doing a stretch or exercise on each leg. This will help you see differences in strength, balance, and flexibility.
- How long can you stand on each leg with your eyes closed?
- Does your knee twist on one side when you lunge?
- How far does each leg go when you lie on your back and straighten your hamstring?
2. Address old injuries
In many cases, asymmetries are due to past injuries. The pain or weakness of an injured part of the body can lead to overcompensation in others. Asymmetry turns into a vicious cycle of overcompensation which, due to underuse, causes further weakness on the injured side.
Use GCT balance Biofeedback to correct asymmetries in recovery from injuries or to retrain after adapting to old injuries.
3. Strengthen muscles
To improve running symmetry and overcome imbalances in ground contact time, focus on developing muscle strength and strength.
One-legged (one-sided) Exercises such as lunges and calf raises are effective in developing your weaker leg and preventing the dominant leg from taking over.
4. Optimize flexibility and stiffness
Inflexibility due to injury (e.g. from scar tissue) increases the likelihood of asymmetry. Include flexibility training in your schedule to help overcome tightness caused by injury.
Your range of motion should be specific to your activity. You don’t need the flexibility of a gymnast to run long distances. In fact, having a certain amount of “strength” can actually improve performance. 
A recent study showed that runners naturally adjust leg stiffness and ground contact time to optimize running economy.  A stiffer leg spring will return more energy after compression.
Incorporate single leg plyometrics into your program to improve leg spring stiffness and reduce ground contact time.
5. Vary the terrain
Running over monotonous terrain can worsen the asymmetry. To attempt rwalk over uneven terrain and a variety of gradients to improve proprioception, balance, and strength.
When running on a track, alternate between clockwise and counterclockwise laps to avoid asymmetry from leaning into the curve.