Learning to Fly: Decrease Ground Contact Time | Metric Series #3

by Milestone Sports athlete, Jackie Merritt

“You went FLYING by me out of nowhere!”

You know that person that just seems to fly by you at the end of a race? They are probably flying in a more literal sense than you think! Running faster and more efficiently requires spending more time in the air and less time on the ground.

Husband Jeff Merritt and I flying our way into new half marathon PR’s together last fall! Photo: Memo Sanchez

 

There are a number of biomechanical factors that affect running performance on race day as well as running injury development in training. One of the most influential yet underutilized of these factors is ground contact time (also known as stance time). 

Ground contact time is tied to running performance.

The MilestonePod’s ground contact time metric is the average amount of time your foot spends in contact with the ground on each stride. It is measured in milliseconds (ms). There is a strong inverse relationship between running speed and ground contact time; as running speed increases, ground contact time decreases. This is because as you run faster, you spend more time in the air and less time on the ground. Research shows that ground contact time is related to both running efficiency and maximal running speeds in elite distance runners [1,2]. That is, runners who had the shortest ground contact times used less energy AND could run faster than those with longer ground contact times. Who doesn’t want to run faster with less effort?

Elite endurance athletes who were able to reduce their ground contact times the most were able to achieve faster maximal running speeds. Image: Nummela, Int J Sports Med. 2007.

 

Lower ground contact times can help prevent injuries.

Ground contact time is not only important for how fast and efficiently you run, but also influences important biomechanical factors that are associated with certain types of running injury. The longer your foot is on the ground, the more that can go wrong! Most notably, the longer the ground contact time, the more time the knee has to bend and collapse inwards (i.e. deeper knee flexion and greater knee valgus). Exaggerations in each of these biomechanical patterns can contribute to symptoms of “runner’s knee” and iliotibial band (ITB) syndrome amongst other issues. For runners who suffer from these recurring injuries, ground contact time is a metric that could offer great insight for addressing and preventing these types of injuries.

Good knee mechanics (left) compared to exaggerated knee valgus (right). In addition to hip and core strength deficits, runners who adopt these exaggerated biomechanical patterns tend to have longer ground contact times and are at higher risk for knee injury. Image: http://www.flexibilityrx.com/

 

So what’s a “good” ground contact time?

Even when running at the same speeds, not all runners have the same ground contact times, nor can they reduce ground contact times to the same level when increasing running speed. An elite endurance runner’s ground contact time is usually below 200 milliseconds (ms). That does not necessarily mean that this is your goal, but your ground contact time should be well below 300ms at your baseline running speed. If your ground contact time is already well below 300ms, it may still be worthwhile to train to improve it even more. Even small amounts of improvement in ground contact can have a positive impact on your running performance and mechanics.

What determines a runner’s ground contact time?

Ground contact time is a function of 1) the position of the foot relative to the center of mass at foot strike and 2) the ability of the muscles and tendons in the leg to capture and generate rapid bursts of power. The good news is that both of these factors are highly trainable!

Training Tips to improve your ground contact time:

#1. Incorporate speed training into your weekly routine. This is probably the most simple and effective way to improve your stride power and ground contact time. At least one time per week, incorporate “striders” into your running routine. These are sets of short (10-20 second) sprints at near maximal running speed. I usually perform 6-8 repetitions of striders at the end of an easy run each week. Striders are very beneficial for conditioning both your musculoskeletal and neuromuscular systems to generate hard fast bursts of energy.

Getting in some striders after a run!

 

#2. Practice plyometric training and (heavy) weightlifting. Plyometrics and strength training will help condition your muscles, connective tissues, and nervous system to improve your body’s power generating ability. When I strength train, I implement some of these principles by performing repetitions fast in the concentric phase of the muscle contraction, slow in the eccentric phase (e.g. for a calf raise, this would be fast on the way up, slow on the way back down).  Box jumps, jumping rope, single leg hops and other similar activities can also be effective types of plyometric training.

[RIGHT] Incorporating quick bursts of concentric movement, such as on the way up during a weighted calf raise, is a great way to increase power generating ability in muscles and tendons that help push you off the ground into the flight phase of running.

 

#3. Increase your running cadence. Slightly increased running cadence is a great option to reduce “overstriding” or landing with the foot too far in front of the body. When the foot lands too far in front of the body, it takes more time for the foot to travel through the stance phase of gait and thus ground contact time increases. The increase in your cadence does not need to be dramatic. A 5-10% increase above your baseline can be highly effective.

[LEFT] Here is some Pod data from one of my easy training runs where I practiced manipulating my cadence. You can see from these graphs that even with a relatively even pace, my ground contact time changed over the course of this run as I changed my cadence. At the beginning of the run I was focused on maintaining a high cadence, but after 10 minutes my cadence decreased and my ground contact time got longer. Pretty cool-and I realized I had some work to do!

#4. Lean your trunk forward. If your foot is landing too far in front of your center of mass, implementing a slight forward trunk lean can be beneficial. Try engaging (lightly flexing) your front abdominal muscles and your butt muscles while you run and lean slightly forward from the ankles (not the hips). This is a very subtle adjustment. The goal is to help your foot land more directly under your body, reducing ground contact time and facilitating a more powerful propulsive force at push off (to help you fly of course!).

Do #3 and #4 sound familiar? You can also reduce your rate of impact forces with these tips! See Metric Series #2

Reducing the amount of time your feet spend on the ground is one of the best things you can do to improve your running speed, efficiency and reduce your risk of injury. Decrease your ground contact time and learn to FLY!

Happy trails!

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References:

1  Nummela A1, Keränen T, Mikkelsson LO. Factors related to top running speed and economy.Int J Sports Med. 2007, Aug 28(8): 655-61. https://www.ncbi.nlm.nih.gov/pubmed/17549657

2 Chapman, Robert F.; Laymon, Abigail S.; Wilhite, Daniel P.; McKenzie, James M.; Tanner, David A.; Stager, Joel M. Ground Contact Time as an Indicator of Metabolic Cost in Elite Distance Runners. Medicine & Science in Sports & Exercise Issue: Volume 44(5), May 2012, p 917-925. Link

 

 

 

Author: Jackie Merritt

Jackie is an accomplished ultra-runner and an avid MilestonePod data fan. She has a Doctorate in Physical Therapy and a PhD in Biomechanics. She lives and trains in Atlanta with her husband Jeff and the Yeti Trail Runners. When not running, Jackie works as a PT and research scientist at Emory University School of Medicine. Jackie also runs for Hoka One One and NATHAN Sports.