Recently, the Science of Multi-Directional Speed team, in collaboration with our friend Dr Damian Harper, published an article in Sports Medicine, highlighting the potential of high-intensity horizontal decelerations as another key performance indicator and potential injury mitigation strategy in team sports (Deceleration Training in Team Sports: Another Potential ‘Vaccine’ for Sports-Related Injury? | SpringerLink). We felt this discussion shed some much-needed light on the important role that assessing, training and monitoring horizontal deceleration has within a high performance team sport setting, and we have already seen evidence of this now being incorporated into thoughts and practises within the speed training world (Misconceptions About Speed and Power Training for Team Sports (simplifaster.com)). As such, this next post will aim to provide a brief overview of this discussion and attempt to discuss some more applied implications for sports science and medicine practitioners in the field. Getting our athletes sprinting faster has been highlighted as a fundamental component of conditioning practices in elite team sports, with its potential to ‘kill two birds with one stone’ in relation to both performance and injury mitigation; we consider that the same may be true for ‘slamming on the brakes’ and slowing our athletes down.
Background
We define a horizontal deceleration as “the action performed during sporting scenarios that precedes a change of direction (COD) manoeuvre or an action immediately performed following a sprint to reduce momentum.” Crucially, high-intensity decelerations are linked to movement patterns commonly performed in match play, where athletes need to rapidly reduce momentum in order to evade or pursue opponents during offensive and defensive scenarios. The performance of horizontal decelerations in team sports present unique biomechanical (i.e., kinetic, kinematic and spatiotemporal) and physiological (i.e., metabolic, neural and muscle-tendon unit) characteristics, potentially possessing different load-response rates in comparison to other key performance indicators (KPIs). The high braking demands of horizontal deceleration requires active muscle lengthening (i.e., eccentric muscle action) and have the potential to generate greater mechanical loading, characterised by ground reaction force profiles of high impact peaks and loading rates. Consequently, in comparison to other KPIs, such as high-intensity accelerations and sprinting, these stressors may be as fundamentally different, which should be characterised, trained and progressively overloaded differently within a training cycle (Vanrenterghem et al., 2017)
“We define horizontal deceleration as the action performed during sporting scenarios that precedes a change of direction manoeuvre or an action immediately performed following a sprint to reduce momentum.”
Implications for Injury Risk and Performance
In our review article published in Sports Medicine, we centred discussion around the potential injury risk implications of high-intensity horizontal decelerations in team sports. However, as we have discussed previously, sports science and medicine practitioners should understand that certain athletic training methods may present a dual benefit with respect to simultaneously enhancing performance and reducing the relative risk of injury. Indeed, the value of regular, appropriate and progressive exposure to sprinting and eccentric exercise for our athletes has previously been highlighted (McBurnie et al., 2021; McCall et al., 2020; Mendiguchia et al., 2019, 2020). As such, this next section will discuss the implications of horizontal decelerations on both injury risk and performance, but particularly how striving to improve both elements may, in fact, come hand-in-hand.
Injury Risk
Deceleration actions play an important role when reducing whole-body momentum, particularly during the execution of sharp-angled CODs or when running at high velocities (Dos’Santos et al., 2018). However, due to their propensity to generate high multi-planar knee-joint loading while the foot is planted, these rapid directional changes and decelerations have been shown to be inciting movements associated with noncontact lower-limb injury, such as anterior cruciate ligament (ACL), medial and lateral ankle sprains, groin, and hamstring strain injuries. Furthermore, due to the high eccentric braking demands of deceleration (i.e., lower-limb internal extensor moments), these actions may be linked to eccentric-induced muscle damage, as evidenced by the elevated levels of indirect muscle damage biomarkers (e.g., ↑ creatine kinase) in the 72-h period following repeated sprints with intense decelerations, as well as post-competitive match play. Importantly, the diminished ability to tolerate high force eccentric actions under fatigued conditions may lead to a catastrophic loading event which exceeds the structural tolerance of the tissue and lead to muscle strain. Conversely, a more chronic consequence may be incurred as a result accumulated tissue damage through summative and repetitive loading events, subsequently surpassing the remodelling rate of the biological tissue and leading to the phenomenon known as ‘mechanical fatigue failure’.
In essence, through both reduced physical capacities and movement skill, athletes who demonstrate poor horizontal braking ability may present an increased likelihood of accentuated eccentric-induced tissue damage and experience amplified multi-planar knee joint loads during COD (i.e., ↑ ACL injury risk). Over the course of a long, heavily fixture-congested competitive season, an under-prepared team sport athlete may find themselves in a vicious cycle of ever-increasing neuromuscular fatigue and tissue damage, with the accumulation of tissue micro-trauma leading to chronically elevated fatigue levels, reduced movement proficiency, and the inability to effectively attenuate braking loads, subsequently heightening injury risk (Harper & Kiely, 2018).
The ‘Vaccine’
Exposure to eccentric-focused exercise has been shown to induce positive shifts in muscle architecture, characterised by the differential addition of sarcomeres in-series (Franchi et al., 2017). This will likely enhance muscle function by inducing a concurrent shift in the ‘optimal’ force–length and force–velocity relationships of the targeted muscle; these mechanisms may be considered ‘protective’ through enhancing the muscles’ maximum shortening velocities, as well as the maximal forces produced at longer muscle lengths, subsequently mitigating eccentric-induced muscle damage. Rapid pre-activation in the muscles is also critical in this respect, in which the increased muscle thickness and pennation angles (i.e., muscle gearing) may further enhance the mechanical tolerance of the muscle (i.e., ↑ force-velocity potential), also supporting the knee joint loading demands placed on the ligaments on ground contact. Additionally, the muscle tendons’ role as the ‘series-elastic shock absorber’ may lead to it withstanding a large proportion of mechanical loading experienced within the muscle-tendon unit during deceleration. This mechanical buffering capacity may serve to reduce the rate of active muscle fascicle lengthening and mechanical strain imposed on the muscle fascicles.
From a biomechanical perspective, the multi-step nature of COD actions points to preliminary deceleration as a fundamental strategy for reducing momentum and subsequent knee-joint loading during the final foot contact of COD (DosʼSantos et al., 2019). This can be considered a modifiable risk factor for ACL injury mitigation, with a key characteristic of effective braking being able to generate higher magnitudes of braking impulse in the steps prior to COD foot plant and dissipating these braking forces over multiple foot contacts, within greater knee flexion ranges and generally performed in the sagittal plane, which is considered a safer strategy. Resultantly, the synergistic blend of rapid pre-activation ability, mechanically robust tendons and highly proficient movement execution play critical roles in moderating the high mechanical loads experienced within the musculoskeletal system during high-intensity decelerations, and thus, protecting the athlete from the damaging nature of these actions.
A ‘Win-Win’ Strategy
Alongside inducing favourable adaptations in relation to muscle cross-sectional area, architecture and activation patterns, the use of eccentric overload training can also improve eccentric strength capacity, with resistance methods now commonly employed, such as tempo eccentric training, flywheel inertial training, or accentuated eccentric loading (Suchomel et al., 2019). As such, the adaptations developed from eccentric-focused resistance training are also likely to be beneficial for athletic performance, as demonstrated by the positive effects this form of training has on both linear and COD speed performance (García-Ramos et al., 2018). However, we would like to underscore that movement velocity, as well as contraction type, may be a key regulator in the beneficial adaptations gained from this type of training (Figure 2).
“The synergistic blend of rapid pre-activation ability, mechanically robust tendons and highly proficient movement execution play critical roles in moderating the high mechanical loads experienced within the musculoskeletal system during high-intensity decelerations, and thus, protecting the athlete from the damaging nature of these actions.”
Therefore, in theory, deceleration training may be a high-velocity eccentric strength training method that could elicit advantageous changes in neural, morphological and mechanical characteristics, particularly when periodised and programmed accordingly. The high velocity component of this training method could be essential for injury mitigation, due to higher associated muscle-tendon forces, which are often difficult to target within a weight room. Indeed, promising results have already been demonstrated as a result of enforced stopping training (Lockie et al., 2014), where the authors reported favourable changes in knee extensor and flexor concentric and eccentric peak torques and reactive strength. We feel this simple training method could be a potent stimulus to induce lower-limb fast eccentric velocity strength adaptations easily in the field as an isolated training session or integrated into the warm-ups prior to technical/tactical sessions. Future work is certainly needed to confirm the efficacy of this method on performance metrics, as well as muscle strength, architecture, and activation patterns, alongside the the minimum effective dosage of deceleration training in different settings. However, we advise a conservative approach to the programming and periodisation of deceleration training and recommend that practitioners consider both the volume, intensity and density of horizontal deceleration exposure at both the acute and chronic level. For example, high-intensity deceleration distances or frequencies derived from match play tracking technologies may provide a good indicator of session volume, also manipulating approach velocities and stopping ‘windows’ of deceleration-focused drills to regulate session intensity (see page 7; McBurnie et al., 2021). It is also recommended that practitioners limit training increases to <10% per week and use markers of fatigue as a guide for training progression or regression (i.e., physiological, neuromuscular or subjective).
In actuality, excellent work led by our own Tom Dos’Santos has already shown the positive effects that targeted multi-directional speed training can have on both improving cutting and pivoting performance times, mechanics, and movement quality in team sport athletes (Dos’Santos et al., 2019, 2021). Within both interventions, a key emphasis was placed on developing deceleration mechanics and COD technique through targeted drills and coaching. This was formed on the basis of fundamental role that the penultimate steps have in both facilitating optimal performance and regulating the knee joint loading demands during COD (DosʼSantos et al., 2019). Crucially, the training methods employed in the above discussion were underpinned by a coaching philosophy that used a blend of previous experience and scientifically supported, theoretical rationale (Dos’Santos et al., 2018; DosʼSantos et al., 2019; McBurnie et al., 2021; McBurnie & Dos’Santos, 2021).
Accordingly, the final sections in this article will provide some suggestions on how to incorporate high-intensity horizontal decelerations within a team sport athletic training programme. Much more research is required to substantiate the suggestions that follow and readers should interpret these recommendations within the context and realities of their own environment. However, just as sprinting has rightly received much attention for its dual performance and injury resilience benefits, the importance of high-intensity decelerations may need to be considered in the same light.
Integrating Deceleration Training into the Weekly Microcycle: A Soccer Example
The use of tactical periodisation has become a popular planning approach adopted in elite soccer, owing to the simultaneous development of the technical-tactical and physical components of soccer it promotes within the weekly microcycle. With an understanding of the teams ‘game model’, the key fitness qualities associated with success in soccer match play can be reverse-engineered and subsequently overloaded through sports-specific means. The dynamic nature of this approach is greatly dependent on the fixture schedule of the team. For example, whether a team has one or two games per week, the logistics of away fixtures, players going on international duty, and many more individual aspects. Albeit, following a conventional one-game per week structure, teams may be presented with a ‘window of opportunity’ in which there is enough time between two fixtures in which to overload the necessary biomechanical, physiological, and neuromuscular fitness qualities while allowing for residual fatigue to have diminished in time for the subsequent weekend fixture (Figure 3).
If these circumstances are present, two ‘acquisition’ training days may be incorporated into the training week which aim to overload the high-intensity game components using ‘intensive’ and ‘extensive’ soccer conditioning themes (Walker & Hawkins, 2018). Briefly, intensive soccer training centres around small-sided games, through the structuring of training parameters with reduced pitch dimensions (e.g., 10 x 15 m) and subsequently high pitch density per player (~10-95 m2), as well as reduced work to rest ratios of drills (e.g., 2:1). These training parameters likely induce significant work to the musculoskeletal system through the performance of a high volume and density of accelerations, decelerations and CODs. Conversely, extensive soccer training aims to expand pitch dimensions (e.g., full pitch) and lower the density per player (~120-350 m2), typically reflecting a more position-specific element to match play, which increases the volume of high-speed work and accumulation of larger total distances, which is a desired physical focus for soccer-specific conditioning. Importantly, it is during these ‘extensive’ conditions in which the attainment of velocities close to an individual’s maximum can be attained within soccer-specific drills.
Although the benefits of this approach are not disputed, it is still often contended that the manipulation of the above sports-specific training conditions (e.g., small-sided games or match play) may not be sufficient to overload key physical parameters, nor do they offer a way to deliver multi-directional speed training in a structured, systematic and progressive manner, while working on movement mechanics, which is vital for improving athletic performance as well as reducing a player’s relative risk of injury (McBurnie & Dos’Santos, 2021). This is why sports teams may seek to closely monitor key variables through the use of tracking technologies (e.g., global positioning systems) in order to ‘top-up’ players with the necessary fitness parameters during athletic training exercises when appropriately identified (Buchheit, 2019). However, similar to how sprinting volume (e.g., distances covered > 25.2 km·h-1) and intensity (i.e., > 95% maximum velocity) have become key aspects to monitor in a team sport environment in this respect, we argue that the same can be true for high-intensity horizontal deceleration exposure. We stress that our understanding regarding the minimum effective dosage and intensity of deceleration training to maintain and/or elicit positive effects currently remains unclear. Nevertheless, through training themes, drill parameters and athletic training methods being sequenced at different times within the training week, practitioners may find a means to target the adaptations that may be conducive to enhanced horizontal deceleration capabilities (Table 1).
Table | Applied suggestions and theoretical rationale for the inclusion of horizontal decelerations within a weekly soccer microcycle.
To conclude, it is hoped that these suggestions provide a sounding-board for future investigations, technological advancements and novel training methods that will be vital to support the evolution of future team sport athletic preparation. We thank you for reading our post and leave you with a summary statement from our review:
“While the continued development and maintenance of high-velocity locomotor activity remains a vital piece to the ‘performance puzzle’ in team sports, it is advised that practitioners ‘do not speed up, what an athlete cannot slow down’, and begin to monitor their athletes’ deceleration activity with more vigilance and appropriately progress training loads with this key feature in mind. During field-based activity, athletes should be regularly exposed to high-intensity decelerations within their weekly microcycle, in conjunction with improving their eccentric strength capacity in off-field training. Furthermore, the development of an athlete’s horizontal deceleration capacity should be delivered through an informed understanding of the mechanics necessary for successful performance and reducing relative injury risk. These recommendations will go a long way to “mechanically protecting” individuals from the damaging nature of high-intensity decelerations and hold special relevance for those tasked with the challenging problem of pushing the boundaries of athletic performance while reducing injury risk.”
McBurnie, Harper, Jones & Dos’Santos (2021; Page 9)
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