Questions 1: Why Are Deceleration Abilities Crucial for Footballers?

A1 Bram Swinnen: That’s an easy question. I think almost all sports are deceleration dominant. We work so much on acceleration, and acceleration, of course, is important. But if you look at football, rugby, and a lot of different sports, most are deceleration dominant, and also most injuries, specifically non-contact injuries, occur during the deceleration phase. It’s what is also called the forgotten factor.

Over those 25 years, I’ve progressively started dedicating a bigger part of my training to eccentric training and also deceleration. In the beginning, eccentric training was considered as odd training. It was something you didn’t implement, certainly not in the season because it caused a lot of muscle soreness, but that’s all been debunked by research, and you have really high effectiveness from eccentric training. And I have progressively started implementing more eccentrics and deceleration training.

A1 Thomas Dos’Santos: Okay. Yeah, great question. So, I think a lot of emphasis has been placed on linear speed recently, probably over the last 15, 20 years. And with the advancements in technology, you need to be able to slow down to reduce your momentum, especially as you get faster. It becomes more challenging with the increased momentum. So, I suppose deceleration is important in two scenarios. You’ve got deceleration as an isolated action itself, so reducing your horizontal momentum. If you take a footballer, for example, they might need to decelerate in reaction to their opponent or in light of a pass or something like that. There are a lot of tactical scenarios where deceleration is highly important as an isolated agility action, but it’s also essential for reducing momentum prior to changing direction actions as well.

In addition to the importance of performance, there is also an injury-inciting mechanism, an event. There have been quite a few studies now highlighting that these deceleration actions and change of direction actions are associated with various injuries. ACL is one of the primary mechanisms of injury that has drawn a lot of media attention recently, particularly in female soccer. Typically, they occur when there are a lot of precedent offensive scenarios where you may need to accelerate and then slam on the brakes once you stop pressing an opponent when they have the ball, and they might try and shift and change direction with the ball, or you try to make some form of interception.

Questions 2: How Do You Test and Monitor Deceleration Abilities?

A2: Bram Swinnen: To test deceleration, we use Photon Sports so you can have an acceleration phase over 5, 10, or increase even to 20 meters that you go to full speed sprints and then decelerate as fast as possible. And then you calculate how much distance you need to decelerate. But you can also measure the force display on the ultimate and penultimate step. So, there are a lot of parameters in Photon Sports, and we use those as testing and testing parameters.

What I used before is, of course, you have eccentric strength. You also have fast eccentric loading; the testing itself was more on an elementary level and still good testing. But I have to admit it’s not sport-specific enough.

A2: Thomas Dos’Santos: So, there are various bits of technology to assess deceleration abilities. There are probably two primary tests where you either accelerate and sprint and then decelerate at a specific distance. It might be decelerate, and once you get to 20 meters, you’re going to decelerate on that cone specifically, or it may be you sprint a certain distance once you’ve passed that point, you then slam on the brakes. So you’ve got the classic test by Damian Harper, the ADA test where you sprint 20 meters. Once you cross that point, you then slam on the brakes and then you can record various metrics. In terms of technology that we can use, obviously, you got Photon, radar technology, lidar technology, optoelectronic technology, potentially GPS, although I’m dubious about the sampling rate of GPS. The beauty of the other bits of technology, I believe that Photon samples at 60 hertz, GPS is typically ten hertz, which I don’t think is enough to actually capture enough data because decelerations occur over potentially a fraction of a second.

Integrate deceleration sessions as part of a change of direction assessment. So as part of the 5-0-5, you would run typically 15 meters, turn about 15 meters, about 180 degrees and come back. So you would need to reduce your momentum to zero. That would probably be a test where you are just decelerating at that specific distance. So you could get to, for one kind of test your incessant change of direction ability or 180-degree change direction ability. But if you have got access to technology such as Photon or any other bit of technology that gives you instantaneous velocity, you could start breaking down that 5-0-5 into different phases.

Question 3: How Often Should Deceleration Abilities Be Tested and Monitored?

A3: Bram Swinnen: We test as much as possible. So every time, yeah, we work with sensors during strength. So Smart Coach or Output Sports for acceleration, average speed, peak power, we gather everything we can gather. And of course, more sports-specific exercises like yeah, the deceleration phase. We tested Photon Sports. So what I like is I implement it into training, for me, every training session is a testing session because you have so many fixtures in football, it’s difficult to have separate testing moments.

A3: Thomas Dos’Santos: From my bias, I would probably do it quite consistently and often. I suppose it comes down to resources, logistics, and your head coach how much time they would give you to do the testing and the time of the year. Normally if you were in a football club, they probably would have periodic testing every three or four times a year. So maybe start of a pre-season period. I probably wouldn’t do it at day 1, going into maximum velocity sprints and high-intensity decels. But after a few weeks, once they build up that capacity, at some point of pre-season, end of pre-season mid-season towards the end of the season. I would argue it’s negligent to not be evaluating deceleration capabilities of your athletes if your sport involves multidirectional movements and deceleration movements. I think there are a lot of solutions available now, and we should be doing it periodically over the course of the season because we’ve got a duty of care to make sure our athletes are physically prepared for the demands of their sport. If you’re not evaluating deceleration capabilities, how do you know that they’re capable to meet the demands of the sport?

Question 4: Which Key Performance Indicators (KPIs) Should Be Focused On?

A4: Thomas Dos’Santos: In terms of the key metrics, so you can measure after your peak deceleration values, but essentially you want to have a little stopping distance and do that in as short an amount of time as possible. So being able to break hard late and fast, if you think about it, sport, you want to be able to outmaneuver your opponent and be able to slam on the brakes quickly over a short time interval and as little distance as possible to create separation or react to your opponent. So braking distance, time to stop, average and peak deceleration, approach velocity, or momentum.

A4: Bram Swinnen: The distance of deceleration from full speed. So you have the distance, you have the balance, and the penultimate the ultimate step and also the power output. So you have a lot of different KPIs a lot of times because Photon Sports, they also develop their test based on the test of Damian Harbor, who’s a specialist in deceleration.

Also, if we look at the change of direction. So change of direction; What’s very important, That’s the horizontal force production during deceleration, during the penultimate and the ultimate step contact times and also of course horizontal force production sprinting out of the change of direction. So I think we did horizontal force profiling. You can do that with Photon Sports maybe in the deceleration. That would be also an interesting one to have an idea on the horizontal forces that you produce during deceleration for sprinting.

Question 5: How Should You Act on the Test Results?

A5: Bram Swinnen: If you see, for example, that players proportionally, they need a lot more distance to decelerate, the landing impulse is lower. Yeah, of course, that means you have to focus a little bit more on eccentrics. Maybe just start with elementary exercises, then go to development and then go to sport-specific exercises. But with at least that have a proportionally longer distance to decelerate that deceleration abilities are not as good. I would increase deceleration exercises or eccentric exercise, the proportion of eccentric exercise and deceleration in their training schedule.

You also see that a lot of times, for example, after ACL return, turn-to-play on ACL. You have a lot of test batteries, but everything is like task-specific. But the moment that dual-task come into play, the decision making comes into play. Yeah, That mechanics deceleration mechanics or landing mechanics that they deteriorate, they become worse and that’s also what we need to implement in rehab. We need to implement more dual-task Because that’s the way daily life and especially sports, it’s always a cognitive overload.

A4: Thomas Dos’Santos: It all depends. I suppose it comes down to logistics resources about the staff that you have. Ideally, we should be trying to drive individualized testing. I would completely appreciate it If you’re a strength and conditioning coach and you’ve got 40 athletes to work with and you’ve only got two sessions per week of an hour, each going to be quite difficult for individual as everything but where possible, individualized where possible. You could start to put people into buckets depending on their results. So I think the first step is looking at those KPIs. How well did those athletes perform and then start identifying do they exceed average? Are they below average? Based on whether your normative data is or where they rank maybe within the squad?

Question 6: What Happens When Technology Makes Testing Easier and More Accessible?

A6: Thomas Dos’Santos: Now great question. So I think we are in an exciting time with technology continually evolving and advancing at really high-pressure environments, particularly working in sports where time is precious. So I think everyone appreciates that testing is important, but you don’t want to be spending days and days and hours and hours trying to collect the data. But also you have to be able to act on that data in a forward drive, interventions or discussions as part of the MDT. So if people want to trace one key aspect of bits of technology that kind of encourage that element, you need, I suppose, sufficient testing protocols. So from self using the Photon technology previously it seems to work very quickly. You can probably test an athlete a few trials in a few minutes and if you have a bit of a carousel effect so you have multiple athletes trying it at the same time it shouldn’t take too much time. The key thing is getting data back. So, yes, we’ve done this testing. What does that mean for the player? And then how well do you visualize that back to your key stakeholders, of the player? Where do they need to work on? Where do they rank, where are their strengths and areas of improvement?

A6: Bram Swinnen: I think the biggest advantage is that at this moment we can implement testing into training. So before it was not possible because the setup was too complicated, it took too much time. And that’s a big advantage of improved technology that the testing doesn’t interrupt the flow of the training. So every training session can be a testing session. I think that the mind-shift has come a lot faster in the last one or two years, because also what you see in research is the focus, the importance on movement strategy, not just performance. And also, of course, data gathering. We don’t do only testing, like for performance testing. With a lot of things, we use what we call fatigue testing. So we want to have a good idea of the neuromuscular performance of the player and fatigue of the player so we can adapt a program a little bit based on those results.