Ground Contact Time, Cadence and Injury


Sometimes you come across information on the web that is…questionable? I don’t want to throw any particular person under the bus so I won’t provide the links to these quotes. However, I’ve been coming across some sites lately with some interesting quotes on ground contact time (GCT – the amount of time your foot spends on the ground during one step) such as:

GCT and cadence:

“Increasing your cadence reduces the amount of ground contact time”
or…
“A higher turnover rate reduces the amount of time the foot spends on the ground, also known as ground contact time”

GCT and injury:

“Injuries occur only when there is ground contact. So if you reduce the ground contact time, you reduce the risk of injury.”
or…
“The shorter your ground contact time, the less chance for injury”

So, are these statements tue?
Very briefly, GCT is measured by the amount of time one foot spends on the ground during one gait cycle. In general, GCT decrease as speed increases also, heel strikers generally have longer GCT and GCT usually increase as fatigue sets in. Is it true that cadence has a strong relationship to GCT? Yes. And is it true that faster runners generally have short GCT’s? Yes. However, if the goal is to reduce GCT for everyone, that seems like a silly idea to begin with. Reducing GCT comes at an increased metabolic cost according to many studies. This is great if you’re a sprinter, but a long distance runner? Maybe, but it depends on a few things.

But I digress…

Part 1: Increase your cadence to reduce your GCT

With respect to the first idea – that a faster cadence always reduces the ground contact time, that just simply is not true. Below, I submit a video of two different patients running approximately the same speed. I measured both of their cadences and they are both just over 180. However, I also measured the GCT, and this is what happened: (keep in mind, I wasn’t using high tech accelerometers/force plate etc. so it’s not incredible accurate, but it’s obvious in the video where the differences are)

[vimeo]https://vimeo.com/56779196[/vimeo]

Before we go any further, we all need to pause for a moment and reflect on how cool the intro to that video was!

OK, moving on… there are many examples of what we saw in the video, but the point remains – a faster cadence doesn’t always mean less ground contact time for everyone. Not all runners have the same GCT at the same speed. Not all runners have the same GCT at the same cadence. As cadence increases not all runners decrease the GCT at the same rate.
If you don’t understand that, read the part below on the blue writing.

One step length is measured as the distance between one foot fall and the opposite foot fall.
One stride length is measured as the distance between foot falls of the same foot (2 consecutive step lengths equals one stride length)
Cadence is the number of steps per minute

One step length includes the ground contact time of one foot PLUS the flight time until the opposite foot touches the ground. This means that I could potentially increase my cadence simply by reducing the flight time. By reducing the flight time, the step length would be shorter and cadence would be increased (assuming the same speed). However, I never changed my ground contact time.

There are lots of speed walkers who have high cadences and no flight phase of gait, therefore very long GCT. In fact, here is a video of a champion speed walker. His cadence is 206, and guess what? It’s all ground contact! So let’s not say that increasing your cadence always decreases GCT.

Part 2: Reducing the GCT reduces your chance of injury

Back to the two runners in the video and the questionable claims made on some other websites – the second idea that reduced GCT will reduce the chance of injury. This assumes that the bottom runner in the video will have less chance of being injured. Hmmmm…..which of the GCT’s in the video above is better for reducing injury?

Unfortunately, I have been unable to find any literature demonstrating that shorter GCT is associated with less injury. I did a few different PubMed searches and was unable to come up with anything. However, one article (thanks Blaise!) examined 130 female and 70 male runners and found that amongst the male runners, a shorter GCT was associated with an increased risk of injury.

A causal relation? No, but an association at least. They attributed the shorter GCT to increased leg stiffness (“leg stiffness” in this case refers to the stiffness of the leg spring, not the flexibility of the leg). The authors go on to say ” To the best of our knowledge no research has been done to examine the effect of leg stiffness on the incidence of (running related) injuries” If anyone knows differently, I’d love to hear from you.

Since one study is just that – one study, I won’t take it as the end of the argument, but it was a pretty well designed study.

So with respect to GCT and injury, one could argue either way: a shorter ground contact time could mean that you are landing closer to the center of mass and then lifting the trail foot quicker. This should result in less sagittal plane acceleration/deceleration and thus less risk of injury. However, a shorter GCT also means that you must be generating the same amount of force over a shorter time period which would mean less force dissipation and a stiffer leg. This would increase the rates of force and thus, increase the rate of injury.

So in the end, it’s irresponsible to say that a faster cadence always equals less ground contact time and it’s also irresponsible to say that shorter GCT reduces injury. We do know that faster runners generally have shorter GCT’s than average mom’s and pop’s. Does that mean the average Joe should emulate the short GCT?
Again, if you have any thoughts on this, I’d love to hear from you.

17 Comments so far:

  1. Nice post… no comment!
    I love when we run in grey zone 🙂

  2. John Foster says:

    Some very good points on GCT. You mention that an increased rate of force increases the rate of injury. To my knowledge only tibial stress fractures have been associated with increased vertical loading rates. I’d be interested if you have any evidence of other injuries associated with vertical ground reaction force.
    There is also good evidence that increasing leg stiffness reduces several kinematic parameters associated with ant knee pain. Ie knee adduction and femoral medial rotation to name a few. This suggests that increasing leg stiffness then becomes a desirable change. As far as I am aware a stiffer lower limb is not associated with increased vertical loading rates. Again I welcome any papers you may have to the contrary as I spend a great deal of time stiffening up injured runners.

    • admin says:

      Hi John,
      Thanks for your email. Glad to know someone actually is reading my blog!

      Basically, here is the argument as I see it:
      1) In order to create shorter ground contact time at a given speed, you need to create the same force, but do it in a shorter period of time. I hope we agree on that.
      2) If you are generating the same force in a shorter period of time, by definition, you are increasing the loading RATE. Again, I hope we agree on that.
      3) Increasing loading rate increases risk of injury. I think this is where the disagreement may originate?

      Here are some studies showing that increased loading rate is associated with injury:
      1) Hreljac did a study looking at runners with recurrent injuries vs. runners who had been injury free through their careers. The only biomechanical variables they found that were significantly different were peak impact force and impact loading rate. I have given you a link to the full article: http://www.hhs.csus.edu/homepages/khs/biomechanics/manuscripts/hreljac.runninginjuries.pdf
      2) Irene Davis did a prospective study last year (as yet unpublished) where they followed 242 runners for 2 years. Before they followed them for the 2 years, they measured different variables. Over the 2 years, 57% of them sustained an injury including iliotibial band syndrome, anterior knee pain, tibial stress syndrome and plantar fasciitis. Statistically significant differences included average vertical loading rate and tibial shock values. They stated, “Based upon the odds ratio for VALR (vertical average loading rate), reducing impacts is likely to result in an overall reduction of injury risk.” Here is a link: http://www.asbweb.org/conferences/2010/abstracts/472.pdf
      3) Last year, Bredeweg et al., did a prospective study by measuring variables and then following the runners for 9 weeks (too short if you ask me). There were 203 runners and they found that amongst the males, the injured runners had higher loading rates and shorter GCT. http://www.ncbi.nlm.nih.gov/pubmed/22921763

      So, here are 3 different studies showing higher loading rates are associated with general running injuries. Faster runners generally have shorter GCT’s, and I think that’s where you get running coaches trying to tell their runners to shorten GCT. To me, it just inherently makes sense that a higher rate of loading will correlate with higher risk of injury.
      I agree that to increase speed, you need to increase limb stiffness and consequently, increase loading rates. However, there is increased risk of injury. Ideally, you would want to have a short enough GCT to benefit from elastic recoil of the tissues, but not so short a GCT that loading rates increase to the point of injury.

  3. First of all, congrats on the fantastic intro to the video.
    My query is although the runner at the top has more total GCT than the runner below him, it’s only due to his glancing heelstrike. Is it not the time spent in midstance that is more significant and the basis for increasing cadence? As far as I am aware, peak loads occur at midstance and toe off, as shown in the study by Scott (1990) which led to the finding that “the impact force at heel contact was estimated to have no effect on the peak force seen at the chronic injury sites.”

  4. admin says:

    Yes, thank-you for the congrats on the video intro. Let’s be honest, who cares about the content of the video when the intro is that cool. 😉
    OK, all silliness aside, I agree with all you said:
    1) Peak loads do occur at midstance and there is no (or at least conflicting) evidence that peak loads are correlated with injury. However, peak loading RATES are associated with injury. Since loading RATES are associated with shorter GCT as well as increased leg stiffness, we can infer that shorter GCT and increased leg stiffness would also be associated with higher rates of injury. Of course, this is assuming a great deal. OTOH, the point of this blog post was to refute some people’s claim that decreased GCT will help REDUCE injury. There is certainly more evidence that decreased GCT increases risk of injury, not decreases it. Again, as usual, “it depends” on a number of factors.
    2) Yes, the runner at the top of the video tends to have a glancing heelstrike, however, SHE is still having longer GCT than the runner in the bottom of the video. I admitted at the top of the article, this is all rough estimation based on a 60 fps camera without accelerometers or forceplates My point was that increasing cadence doesn’t always equate to shorter GCT, as evidenced by the speedwalker who has a cadence of 206, yet has no flight time and is all ground contact.

  5. Thanks, that makes sense. Please send my apologies to the female runner at top of video. I knew the moment send I was going to regret that!

  6. […] GCT is a contentious topic, in my opinion.  I made a different blog post about it earlier.  On one hand we have good evidence that more elite runners tend to have shorter […]

  7. JEFF says:

    HI- Thanks for the post. I cant see the video, I will check back later to see if it is up.

    I have started Barefoot running about 3 months ago (short time). I have slowly increased my weekly distances and % of unshod to shod running. Yes, I still wear shoes as well.

    Before running BF, I read a book, “Barefoot Running Step by Step, by Ken Bob Saxton” – It seems there is some evidence, but mostly personal experience in this field. Given that, here are some of the suggestions by Ken Bob.

    (1) increase cadence – his point of this, is to reduce impact. You arent necessarily trying to go faster at this point, but to reduce impact. As Ken Bob states, “you have 2 coaches with you all the time” – you will feel if there is an impact when you are running BF. Trust me. So, the goal assumes, increasing GCT will decrease injury. (even if its minor ouchies on your feet) – but then I would extrapolate (as Ken Bob has also suggested) that this impact is then transferred to your ankle, knee, hip and back. Therefore reducing the initial impact, and further reducing the transferred impact by adjusting the angle of the ankle, bending your knees, lifting your knees (hips) will have an overall negative (good) change to the forces applied to those joints.

    (2) decrease vertical oscillation – (ok, I dont think Ken Bob ever uses this term) but – he recommends keeping your head from bobbing up and down, and to try to keep the horizon steady as you run. His recommendation for this is to reduce wasted energy (you want to go forward, not up) which said another way would be to increase efficiency. I believe the other reason for this, would be to reduce impact forces.

    I am thankful for your post suggesting that shorter GCT does not definitely mean lower injury. I would suggest that it does the opposite. However, this study overall seems to be too small and too short. In time, we will have more information (and more conflicting information to go with it!)

  8. Lane says:

    Thanks for a good read on the topic. I have a background in engineering, and so appreciate the complexities involved in any kind of systems modeling.

    Taking your main points a bit further, there is no single statement “Doing X will/will not result in Y effect” that will apply universally to a system as complex as an individual human in motion.

    Every runner (and run) represents a unique combination of mechanical (musculoskeletal), physical (metabolism, cardio-respiratory), material (tissue), environmental (shoes, terrain, surface, grade) factors that make sweeping generalizations impossible. It is very likely that for the same individual, reduced GCT would reduce injuries in some running conditions but not others.

    The ultimate judge of these things must be the individual. Careful training and monitoring is the best guide to minimizing injury. Blindly following advice from so called experts is a sure fire way to injure yourself.

    Remember: Pain is information. Pay attention to it and learn from it.

  9. Paul says:

    Very interesting topic, esp with the Garmin 620 coming out that can measure GCT for the average runner.

    I would assume that shorter GCT would be more economical since storing energy in muscles probably doesn’t work for very long. (unlike a metal spring). And there is the observed correlation between faster running and shorter gCT….kind of a ‘duh’.

    statements like ‘ you can’t get injuried if you aren’t in ground contact’ to support short GCT implying less injury deserve nothing but an eye roll 😉

    What i would like to know is “at a given cadence, does a shorter GCT mean a faster runner?”

    • Kevin Maggs says:

      Hey Paul,
      I agree with you.
      The short answer to your question is “no, not necessarily.” Generally, shoter GCT is a trait that you see in faster runners, but not always the case. My point in the article is that many coaches read that shorter GCT is a trait seen in good runners, so they coach their middle of the pack runners to try and emulate that style. This ends up in higher loading rates and greater potential for injury. Longer GCT will generally mean more knee flexion excursion, ankle dorsiflexion excursion and hip flexion excursion. Is that a good thing or a bad thing? It depends what you want.
      Any yes, the Garmin that measures the GCT is kind of funny. I have had many patients wearing it and I casually ask them what it does. They always say how cool it is because it measures this and that. When I ask what they do with that information and how they will use the GCT and vertical oscillation information and they look back with a blank face.
      Kevin

  10. Sergio Encinas says:

    Great post man! I could not stop reading!

    I´m a beginner runner, aprox 5km 3/week now. I had a knee injury (chondromalacia) last november (after 1 year walking/jogging/running. Before the injury I managed to run 10km-15km each run), struggled a lot but I went ahead, and now i´m a serious reader of this topic. I´m working on cadence (2 months ago, according to my garmin fenix 2, my cadence was 156, now 180-185 using a metronome) and i´ll keep working on that until a stable rate achieved over 180 without a metronome. My plan is once i achieve my cadence goal, work on my vertical oscillation (which improved along with my cadence. 2 months ago was 10.8-11.8 and now is 6.7-7.3). I don´t know anything about GCT (Mine was aprox 280 and now 253) but i´m curious and decided to look for information. Still don´t know whether to work on GCT or not, but i have plenty of time from now. Thanks for the post, it´s a great start for me… and congratulations! Sergio.

    • Kevin Maggs says:

      Sergio, if you increased your cadence and your training is done in a reasonable manner (not too, much, too fast, too often) and you STILL are having the knee pain, you need to either have a gait analysis by a competent clinician, or go to see a competent clinician to evaluate the mechanics of your ankles, feet and hips. You also would have to possibly get a proper exam and possibly imaging of the knee to see if, in fact, it is chondromalacia patella and not some other cause of knee pain.
      Good luck!

  11. […] If you’re STILL hungry for more info and you want to read more, I posted this piece on cadence and ground contact times – more on the loading rates in the comments section of the […]

  12. […] year. If you’re STILL hungry for more info and you want to read more, I posted this piece on cadence and ground contact times – more on the loading rates in the comments section of the […]

  13. ginsling says:

    Bit late to the party but have to say as N=1 and using a foot pod and GPS watch for measurements – my GCT doesn’t change a whit whether my cadence is around 160 or around 180 – all that changes is my stride length at a given speed (the same for both cadences) and when upping the cadence I feel like a cork bobbing on water. The only way I can reduce my GCT is when I significantly up the pace doing fast intervals – my stride rate increases as well as stride length.

    The only remedy for my languid GCT is to stiffen my achilles so that it loads fast enough for the recoil energy – and that’s through plyometrics. If you have a stiff achilles and up the cadence, then more than likely the GCT falls. But if you are like me and the reactive force dissipates before the achilles loads, simply upping the cadence achieves nothing more than adding to the range of neuromuscular responses.

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