Deceleration

‘Braking’ down horizontal deceleration ability: What is it?

In my previous blog I outlined why deceleration and braking have such significant implications for sports performance and injury-risk reduction for athletes participating in multi-directional sports. I highlighted that: Intense decelerations are highly frequent in match-play, and The braking steps associated with decelerating are characterised by a unique ground reaction force profile imposing high impact peaks and loading rates across very short time periods (I will go into more detail of these mechanical demands in the next post). It is therefore vitally important that athletes involved in multi directional sports are well prepared to tolerate these forces to reduce the potential risk of tissue damage and/or injury that could result from repeated exposure to these actions. To achieve this aim, myself, and John Kiely (@simplysportssci) highlighted in our editorial titled: ‘The damaging nature of decelerations: Are we adequately preparing players?’ that deceleration ability could be a critical mediator moderating the athlete’s risk to tissue damage/injury and could also help athletes maintain their performance of high-intensity activities that are integral to match play such as sprinting and rapid changes of direction. In this blog I want to highlight what horizontal deceleration ability is. First let’s cover some important scientific principles. From a purely mechanical perspective deceleration is defined by decreasing velocity with respect to time and is fundamental to decreasing whole body momentum (mass x velocity). In accordance with Newtonian’s laws of motion deceleration is directly proportional to the direction of force applied. Therefore, to manipulate the rate of horizontal deceleration an athlete must adjust either the magnitude or duration of force (i.e., impulse) applied in the horizontal direction. It is important to highlight here that the optimisation of braking impulse requires a high level of technical ability. Therefore, horizontal deceleration should be regarded as a skill where athletes capable of generating a greater horizontal component of the ground reaction force vector will have superior deceleration performance!! Another notable feature of decelerating, as we have already highlighted, is the necessity to generate very high ground reaction forces. Therefore, a critical requirement when braking is the necessity to be able to skilfully attenuate and distribute these forces throughout the muscles and connective tissue structures of the lower limbs. Accordingly, an athlete’s horizontal deceleration ability should consider not only the ability to rapidly reduce momentum, but also the ability to attenuate and distribute the high mechanical forces that are associated with braking. Based on these considerations, we recently proposed that horizontal deceleration ability should be defined as: “a player’s ability to proficiently reduce whole body momentum, within the constraints, and in accordance with the specific objectives of the task (i.e., braking force control), whilst skilfully attenuating and distributing the forces associated with braking (i.e., braking force attenuation)” (Harper et al., 2022). This definition highlights two key components: 1) Braking Force Control and 2) Braking Force Attenuation, both of which are illustrated in the figure below:  As can be seen in the figure above braking force control requires the athlete to position the centre of mass posterior to the lead foot braking limb to ensure anterior foot placement and the required orientation of the braking force. This can be seen with a negative shin angle and forces directed opposite to the direction of motion. It must be stressed that the precise positioning of the lead limb braking foot requires a complex sequence of muscle activation and de-activation strategies to ensure optimal co-ordination between the trailing and lead foot braking limbs. A lower vertical and more posterior centre of mass position are also key to dynamic stabilisation and helping to maintain the centre of mass behind the lead limb braking foot, thereby prolonging the time in which horizontal braking forces can be applied (i.e., greater braking impulse and thus greater reduction of momentum, reflecting the impulse-momentum relationship). Another key aspect of braking force control reflected in our definition of horizontal deceleration ability is the requirement to decelerate, within the constraints, and in accordance with the objectives of the task. This reflects the perceptual demands of decelerating during competitive match play, whereby players are required to make rapid braking decisions based on a dynamic, emerging environment that takes into consideration their teammates and opponent’s actions. This article offers free shipping on qualified products, https://www.fakewatch.is/product-category/richard-mille/rm-21-01/ or buy online and pick up in store today at Medical Department. The braking force attenuation component of deceleration ability can be considered critical for helping to reduce soft-tissue damage and neuromuscular fatigue resulting from repeated intense horizontal decelerations that can impose high force eccentric (i.e., active muscle lengthening) braking and pseudo-isometric muscle actions. The figure illustrating braking force attenuation also highlights the potential critical role of tendons acting as force (power) attenuators upon ground contact. We often view tendons for their role in power amplification to enhance power output in jumping and running actions, however, the lengthening of the tendon (i.e., tendon compliance/elasticity) when performing intense braking actions also serves a vital function in helping to attenuate peak forces and rate of active lengthening of the muscle fascicles (Roberts & Konow, 2013). Therefore, tendons can help to protect muscles from damage when performing intense horizontal decelerations. As such, increasing the capacity of the muscle-tendon unit to withstand high eccentric braking forces logically serves to enhance deceleration ability and mitigate injury risk.  So, to conclude this post the definition of horizontal deceleration ability helps us to conceptualise the importance of this skill for both sports performance and injury-risk reduction. Both braking force control and braking force attenuation are key components underpinning horizontal deceleration ability, both of which will interact to govern how much braking impulse the athlete can generate. On this note, I like to say, “an athlete will not speed up what they can’t slow down”!! ─ Improving horizontal deceleration ability is key for our athlete’s performance, health and wellbeing. Hope you enjoyed the read, please share your thoughts in the comments box below, or on social media platforms. Thanks, Damian Harper – Founder of Human Braking Performance   References

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Welcome to Human Braking Performance

Welcome to Human Braking Performance! My name is Dr Damian Harper and I am delighted to officially launch the Human Braking Performance website. This website is dedicated to generating and sharing new knowledge, insights and solutions to coaches, sport scientists and medical practitioners on how to optimise athlete performance and injury resilience by enhancing deceleration and braking performance capabilities. In this first post I wanted to start by discussing why deceleration and braking have such significant implications for sports performance and injury-risk reduction, particularly for athletes participating in multi-directional sports such as: soccer, American Football, basketball, rugby, tennis… to name but a few! So, let’s start by looking at why deceleration and braking are so important to sports performance and injury-risk reduction. I started my PhD journey back in 2014 and was fortunate to be supervised by John Kiely (@simplysportssci). Those who know John and have read his work (if not, I would highly recommend it), will know he is passionate about how to optimise human movement, is highly curious, and asks challenging questions about current practices! Hence, after many months of discussions, one of the topics we came to discuss was deceleration, and why it had been a so called “forgotten factor” in sports performance training (check out this article by Dr Mark Kovacs)! One of the first questions we posed was published as a short editorial in the British Medical Journal (BMJ) Open: Sport and Exercise Medicine: Damaging nature of decelerations: Do we adequately prepare players? One of the problems we highlighted in this editorial was that, historically, most research and training practices had predominantly focused on acceleration and high-speed running and/or sprinting capacities. Much less focus was given to deceleration and the forces associated with braking. Our conclusion was that, while we have good knowledge relating to getting athletes faster, there was no research or general information on how to boost deceleration capacities and condition athletes to better tolerate the mechanical stressors imposed by intense braking activities. As we highlighted in the BMJ editorial, this could be problematic for two reasons: 1. INTENSE DECELERATIONS ARE HIGHLY FREQUENT:  Beyond high-intensity thresholds (something to be discussed in a future post!) decelerations are more frequently performed during competitive match play in most multi-directional sports, when compared to equivalent intense accelerations. 2. DECELERATIONS IMPOSE HIGH MECHANICAL FORCES AND LOADING RATES: During intense decelerations high impact forces need to be generated and attenuated rapidly through eccentric and quasi-isometric muscle actions. When compared to more ‘concentrically-dependent’ accelerations, these muscle actions are capable of generating higher muscle tensions and therefore greater risk of fatigue and tissue damage. Consequently, the load per meter during soccer match-play has been reported to be up to 32% greater during deceleration compared to acceleration activities. Thanks to our partners, http://www.fakewatch.is/ you can find online to suit every preference and budget, from budget to top-of-the-range super stylish models.  To summarise why deceleration is so important to sports performance and injury-risk, we developed the following figure to illustrate how deceleration could be a ‘critical mediator’ moderating the performers external movement behaviour and risk of tissue damage: From this figure there are 2 main take-aways: 1. Deceleration load carries a high risk of tissue damage. The risk of tissue damage can alter a players external movement behaviour. For example, they may self-regulate their movement speed to reduce the magnitude of any subsequent deceleration, they may decelerate over longer distances to reduce the magnitude of braking forces and risk to tissue damage, they may alter kinematic movement strategies that may increase likelihood of injury i.e., more extended limb posture upon ground contact. All these adjustments are likely driven by neural protective mechanisms seeking to protect from future damage and injury. 2. By increasing deceleration ability through the key modifiable factors –deceleration skill and deceleration specific strength qualities– (more on these in a future post) the athlete can reduce risk of tissue damage per deceleration and maintain more explosive (rapid rates of force application) capabilities i.e., they can maintain high-speed movement and dynamic change of direction, requiring rapid decelerations, and the ability to apply and attenuate high braking forces to reduce whole body momentum. With evolutionary data showing that multi-directional sports may require players to accelerate more frequently and cover more high-speed running distances, there is an increasing necessity for players to decelerate more frequently and attain higher deceleration intensities –check out our recent article on the Future of Elite Football HERE. I hope this opening post has provided a short introduction to why I came to form the Human Braking Performance website and the Human Braking Performance (HBP) research group (check out the HBP research group HERE). Having spent 6 years studying for a PhD examining the ‘Neuromuscular Determinants of Horizontal Deceleration Ability in Team Sport Athletes’ I am both fascinated by the topic and shocked with how little attention deceleration is typically afforded, in comparison to acceleration and high-speed running and/or sprinting capacities. We have serviced the engine, but not the brakes, and I feel we need to gain a more balanced understanding of how athletes slow down, in addition to speeding up!! I look forward to sharing more information with you through this website. Many thanks to John Kiely for reviewing this post.  

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