By Carl Valle
The simple measure of how long a foot is on the ground is extremely useful and is a very practical way to see changes in training. Ground contact time (GCT) is a very common measure in sport science, but it’s also an increasingly popular measurement with coaches who manage jump and sprint training.
This article busts myths and shares practical ways to use GCT measures in training. If you are a coach who wants to take advantage of information that guides many of the elite coaches, this article summarizes some of the best practices. Looking at the connection of movement and how long the foot is on the ground is a very direct way to improve athletes, and simple measures are actionable and easy to use.
What Exactly Is a Ground Contact Time Measure?
The period of time between when the first part of the foot touches the ground and the last part of the foot leaves the ground is the contact time. Contact doesn’t mean force, and the ground contact time is just a total duration period and that is it. GCT measures are simple, but they are only useful if analyzed in context. Measuring GCT without having other measures doesn’t tell much, but if a workout includes other measurements or details of the training, recording ground contact times is very practical and insightful.Ground contact time measures are simple, but they are only useful if analyzed in context, says @spikesonly. Click To Tweet
Air or flight time is usually included with ground contact time values, as the duration between each foot strike, whether running or jumping, has additional value. Straightforward metrics of athletic performance like the reactive strength index (RSI) are valid ways to see qualities that coaches want and athletes need. Just knowing how long the foot is on the ground or is not on the ground, and knowing what the athlete is doing while measuring it, is enough information to draw real conclusions.
Contact times on the ground are simple raw summaries, as force analysis and pressure analysis are necessary to see either detail or the reason an athlete is spending more or less time on the ground. Due to the limitations of some technologies, as well as cost constraints, contact times are popular to capture because of the practical nature of seeing simple trends in training or rehabilitation.
Overall, there are three ways to measure a contact time. The most common contact measurement option, though it’s being phased out, is the use of a contact mat. Contact mats are basic sensors that know when a load is on the surface or not. The data, while binary, is good for estimations of jumping. However, due to the fact it doesn’t measure force, it’s assumed that the technique is very strict and can only provide an indirect calculation of height.
A second way is to create a field or grid of lasers that lay just over the ground like an invisible carpet and sense when a foot passes through them. Infrared systems are very accurate and allow coaches to use large areas of measurement and the original surface instead of a mat.
The last way is to use IMU sensors and analyze the data for patterns of acceleration. Wearable sensors are growing in popularity, but it is difficult to use them in sprinting because the data is difficult to see in real time. In the future, foot pods and infrared grids will likely be the standard because of accuracy and/or price.
What Do Ground Contact Times Tell Coaches?
Ground contact times are extremely useful for explaining either why performance is changing or whether a specific variable is trending up or down. It is expected that if you are recording GCT measures with athletes, it usually means you are including other measurements, such as velocity and/or distance. Some deductions are possible simply by knowing the distance and having contact times. When you add in a laser or timing gates, ground contact times become especially useful to coaches. When using GCT measures, coaches can make strong deductions on how forces are created and how those forces influence speed and power.If you record #GCT with athletes, it’s expected you’re also measuring data like velocity & distance, says @spikesonly. Click To Tweet
Much of the idea of developing power is that better rates of force or better applications of force creates better results with athleticism. An athlete running faster by placing more force into shorter periods of time is slightly oversimplified, but generating high rates of high force is the bulk of the challenge with training. Technique without direct instruction, which is sometimes affected by training programs, can modulate how long a foot is on the ground and how it applies force within that time frame.
Most athletic actions are very rapid, so the age-old challenge of using conventional strength training is dicey when trying to squeeze in force development instead of velocity-specific training. The notion that developing a lot of maximal strength and then teaching that quality to use a percentage of it quickly is a rationale idea, but contact times are not the only measure needed to determine whether something is working.
Horizontal speed in conjunction with contact times is the easiest way to see change in performance. Along with speed, the distance between hurdles or step length that is quantified should be enough to see if and how an athlete’s performance is improving. Outside of a stiffness test, contact times by themselves don’t indicate anything unless you have a second measure to compare baseline or previous data. Coaches that now have access to simple measurements can not only develop an athlete with greater individualization, they can also get instant feedback acutely within the session. Without dumbing down contact times, here is one conclusion a coach can make.
“If test or specific performance is improving along with a decrease or maintenance of ground contact time, an athlete is putting more propulsive force into the ground.”
Force analysis can add more detail and far more information to show how the athlete is putting more propulsive force into the ground, but most coaches want to confirm that their recipe for improvement is working. A conventional test, along with ground contact time values, will paint a very complete picture of cause and effect versus correlations that may not be valid.
How to Use Ground Contact Times for Jump Training
More of the discussion on ground contact time comes up with plyometrics than sprinting, mainly because the contact times in sprinting are so short and have less variance. Jumps can be short (ground contact time durations) from simply bouncing with double legs to very extended with the most demanding of depth jumps (long ground contact times). Some charts have categorized various types of plyometrics into specific contact time reference values, but those have failed to live up to the expectations of coaches who have access to contact grids and force plates.
I fail to see the same time periods with advanced athletes all the way down to beginners. My belief is that average ground contact times are empty numbers, and how the athlete creates those scores is what matters. Still, without measuring contact times, it’s hard to decide what is effective with hurdle jumps, as height and spacing are just visual markers and not measurements.Average ground contact times are empty numbers—what matters is how the athlete creates those scores, says @spikesonly. Click To Tweet
Box jumps and hurdle jumps are the two biggest culprits for misdirecting both athletes and coaches. Most of the problem stems from the assumption that the height of a box or hurdle is equal or connected perfectly with the displacement of the athlete’s center of mass. A survival response usually occurs as the athlete hits their ceiling of potential: they lift up their knees and feet higher to succeed, rather than applying better force into the ground to get higher. Many athletes can jump over 42-inch hurdles in sequence, but very few of them do it in a way that creates an adaptation that will transfer later. Ground contact times can’t solve everything, but if we care about better projection, we can evaluate the combination of acceleration of the mass up and distance out and up well without equipment and extremely precisely with the right instrumentation and software.
Biofeedback, be it real-time or immediately after a set of jumping, can teach without the long process of trial and error. The goal with contact time measures is to help calibrate what a coach sees and what an athlete experiences. Removing the contact time measurement burden can relieve a coach from juggling an overload of information. While talented coaches can learn to see more, we are still human and need to handle what drives change in the session and the season.The goal with #GCT measures is to help calibrate what a coach sees and what an athlete experiences, says @spikesonly. Click To Tweet
Immediate data such as air time—the period between contact times—is also useful to access, providing that the athlete creates the time off the ground honestly and productively. These rhythms of air and ground are explained in great detail in Ralph Mann’s book on sprinting and hurdling, and are excellent reference points to what is necessary in elite performance. It’s up to coaches to take Ralph’s data and apply it to practice, as world-class races in August may not jive with practices in January.
The listed ideas are just the tip of the iceberg, as they are simply starting points and not the end game. It’s up to the coaching and sports performance community to explore smarter ways to use contact times in jump training beyond what I share. The use of contact grids and force analysis both in the field and in the lab dramatically adds value to applied approaches to performance.
How to Use Ground Contact Times for Sprinting
Contact times and air times are similar to stride length and stride frequency. While knowing both measures is nice, the key is to know how these two variables influence horizontal speed. About a decade ago, vertical force discussions were popular because Peter Weyand’s research hinted at how valuable stiffness and similar qualities may be to performance. Years later, horizontal forces became of interest, but while some research supported the notion, it was really just an argument useful in a bar during a sports conference—it really didn’t show up as game-changing in practice.
Scientific studies have even explored lateral forces, but like other variables, having one part of the equation doesn’t solve the puzzle. The core issue is the value of allotting resources to specific athletes, and most of the time extreme personalization of training fails because the major influences trump the minor details if done out of sequence. Focusing on ground contact times is important only when a clear plan is in place.
Three primary methods of training exist with ground contact time measurements: maximal speed, acceleration, and fatigue management. Other than these three approaches, I have seen some creative GCT use during hurdle training and wicket drill evaluation. When collecting GCT data, it’s about using it to manage the session and develop the athlete over a career.
During maximal velocity sessions, you can use horizontal speed and ground contact times to see if certain cues, session plans, or past training actually change an athlete.
You can evaluate acceleration with contact times and air times, as well as horizontal velocity, to rank the efficiency of mechanics and the entire run.
Fatigue management is easily visible when both speed and ground contact times decay in performance, and the equipment allows for immediate feedback and actionable decisions.
More advanced analysis is possible, but for the most part, even elite athletes will want these benefits of measuring ground contact times. Deeper exploration, such as looking at the length of contact before and after mid-stance, is theoretically interesting. Talk about pushing and pulling is very finite, actually measuring those variables make those discussions meaningful to coaches. If specific stride parameters are indeed holding back an athlete from improving their speed, a plan to address that variable must be very effective, as most running styles happen to be from genetics and anatomical disposition.
How to Use Ground Contact Times for Agility
Change of direction (COD) is about displacement and elusiveness, and contact time is the name of the game. The creation and closing of space is the soul of most team sports. Agility and COD are not the same, but do have overlapping qualities that must be measured and improved. It is easy to assess ground contact times and what the athlete is able to do with their displacement to see what is more trainable. For example, conventional testing in jumps may not be a perfect relationship with eccentric abilities, but RSI and eccentric utilization ratios are perfectly fine starting points.Agility and COD are not the same, but have overlapping qualities that must be measured and improved, says @spikesonly. Click To Tweet
The most common complaint about contact times are that fast feet don’t usually mean effective use of ground reaction forces. Moving the feet fast doesn’t mean much unless it creates a way to beat a defender or stop an offensive player. Speed ladders have been around for years, attempting to create a fast athlete by having them move their feet up and down quickly, but agility is more about using the forces and movement patterns to fool or dominate an athlete with actual displacement. A few coaches push the visual that an athlete should think jackhammer, not jazzercise.
There are plenty of field tests that show the capacity of change of direction, but agility requires more sport skill than doing 5-10-5 and other tests. Combining sport skills and technique with capacity training is a straightforward way to get athletes better. A true coefficient between on-the-field elusiveness and COD testing doesn’t exist, but athletes with poor eccentric qualities and general speed have a much higher demand to be effective in their sport.
Other Ways to Use Ground Contact Times in Rehab
Most of the research on ground contact times in sports medicine tends to focus on running and not sprinting, but I think the blurred line will disappear between return to play and gait retraining. Asymmetry is a big topic of debate, but instead of thinking about the percentage of symmetry, coaches and therapists should look to see if the difference is caused by lack of actual function or power. Many elite athletes have a history of injuries and have asymmetries, so it’s difficult to separate what is coincidental and what is actually a problem.
It’s perfectly normal to have left and right differences between legs and arms; it’s problematic when the difference is graphic enough that the athlete can’t improve or match earlier performance. The simplest way to look at symmetry needs is to understand that some difference is acceptable, but address it within reason and do not live in fear. While the human body can adapt to many different environments and demands, sprinting faster safely is a luxury and not a primary need.
Humans are not race cars: Race cars break down from symmetry issues because they don’t self-repair and don’t have advanced nervous systems that can hide dysfunction. Capturing baseline data with ground contact times and other stride parameters is useful, and observing changes is a wise investment to decide if future problems are truly severe.
There are several methods of using ground contact times to help bridge the gap between injured and ready for sport. Focusing on improving speed while maintaining short and symmetrical contact times is a great way to build up resilience without increasing unnecessary risk. Use of the RSI (reactive strength index) to manage elasticity during the return-to-play phase is also growing because strength without RFD is not a complete solution. Rehabilitation is about reducing and training around limitations; it’s not just passive therapy. Successful rehabilitation is simply successful training after an injury, and contact times have a tremendous value for everyone involved in return to play.
Before You Invest in a Ground Contact Time System
Ground contact times are like split or running times—not hard to measure, but a big responsibility to improve. Getting someone’s peak velocity is simple and requires no skill or expertise, but improving it is the name of the game. Ground contact time measures add another layer of granularity that reveals so much more than what an athlete can do—they explain how the athlete is doing it. You don’t need to be an expert in what the research says with ground contact times, as your own training easily replicates those measures. Adding in GCT values is easy and shows a direct change that the eye can’t always see.GCTs are like split or running times—not hard to measure, but a big responsibility to improve, says @spikesonly. Click To Tweet
If you are doing a lot of plyometric training or need to develop all speed and agility qualities, adding contact times will deliver direct performance from arousal, and long-term development from better planning and evaluation. For years, I could only use video to get precious information such as ground contact times, and now I find it enormously valuable to add a contact grid to the equation.