To ensure optimal preparation of athletes competing in multi-directional sports, an essential starting point is to gain a thorough understanding of the demands an athlete may be exposed to during competitive match play. Subsequently, practitioners may ‘reverse engineer’ competition requirements through the design of training approaches that most optimally prepare athletes for these specific demands. This has been referred to as reverse engineering (Turner et al., 2022). With the evolution of multi-directional speed sports requiring players to perform more frequent accelerations and high-speed running actions, there is a need for players to perform a higher frequency of intense decelerations and to be able to tolerate a higher frequency and magnitude of braking forces with each limb.
Forces Associated With Deceleration
To put these braking demands into perspective we can examine the ground reaction forces (GRF) associated with intense decelerations and compare these to other high-intensity actions commonly performed by multi-directional speed sport athletes. Figure 1 compares the GRF profile between the first or second step of a maximal acceleration from a standing start (Verheul et al., 2021), the first or second step of a maximum deceleration performed from sprinting speeds around 7 m.s-1 (Verheul et al., 2021), and a step from when an athlete is close to their maximum-velocity sprint running (Bezodis et al., 2008).
The key headline from figure 1 is that the peak forces associated with the first or second step of a maximum deceleration from high sprinting speeds is almost 6 times body mass! This is around 34% greater than the peak forces in maximal-velocity sprinting (4.4 times body mass), and around 168% greater than the peak forces in the first-to-second step of a maximal acceleration (2.2 times body mass). Also of note is the time difference between the occurrence of peak force in each activity. The peak forces in the first-to-second step of a maximum deceleration occurs around 25 ms, which is less than maximum-velocity sprint running (39 ms), and over five times less than the first-to-second step of a maximum acceleration (134 ms). So, in conclusion, the early braking steps from high sprinting speeds have a unique GRF profile, characterised by high impact peak forces and loading rates (i.e., ‘tall-thin’ impulse) that are required to be rapidly attenuated and distributed over very short time periods. Therefore, braking force attenuation is a key component of horizontal deceleration ability.
Interestingly, similar GRF profiles have been observed in the preparatory deceleration steps prior to turning in sharp (> 135°) change of direction (COD) manoeuvres (Dos’Santos et al., 2021; Nedergaard et al., 2014; Santoro et al., 2021). Figure 2 displays the GRF profiles of the antepenultimate (i.e., 2 steps prior to turning), penultimate (i.e., 1 step prior to turning) and final foot contact steps prior to turning in a 135° COD task (Nedergaard et al., 2014). Similar to the first or second braking steps from high sprinting speeds observed in figure 1, the preparatory deceleration steps prior to turning (i.e., when significant deceleration is required) have similar GRF profiles characterised by high force impact peaks and loading rates.
It is important to note that greater ability to generate horizontal braking force in the preparatory deceleration steps have been shown to contribute to faster COD performance times (Dos’Santos et al., 2021; DosʼSantos et al., 2017) and to help reduce the magnitude of mechanical loads that could be experienced in the final foot contact, particularly if sufficient deceleration of whole-body momentum is not achieved in the preparatory deceleration steps (Jones et al., 2015, 2016a, 2016b). Therefore, a better technical ability to brake (i.e., apply greater magnitude of posteriorly orientated braking forces) in the antepenultimate and penultimate footsteps prior to turning could help to reduce the chance of lower-limb injuries (e.g., ACL ruptures) that are commonly seen in the final foot contact when braking during a COD manoeuvre. Interestingly, when compared to males, female athletes have been observed to spend a greater proportion of braking in the final foot contact relative to the penultimate foot contact (i.e., reduced braking force ratio; see equation 1) (Thomas et al., 2020). This could increase the magnitude of forces required to tolerate in the final foot contact and lead to injury-risk biomechanics (i.e., greater knee abduction moments) that are known to contribute to serious career damaging injuries such as ACL ruptures.
The GRF observed in the first-to-second step of a maximum deceleration from high sprinting speeds has also been compared to the plant step of a 90° and 180° COD and a drop jump from 30cm on a 3G surface with and without cushioning underlay (Lozano-Berges et al., 2021). Similar to previous findings the first-to-second braking steps of the maximum deceleration from high sprinting speeds had the highest peak resultant forces, impulse during impact phase, and resultant loading rates (figure 3). Therefore, the authors concluded that the initial braking steps of maximum deceleration from high sprinting speeds to be “the most demanding task in terms of impact force characteristics” (Lozano-Berges et al., 2021, p.673). The loading rate is an indicator of loading severity, and therefore the authors also highlighted the potential for this task to put players at a heightened risk of overuse impact related injuries, especially if performed frequently on hard surfaces. As such, the use of cushioning underlay, as observed in this study (figure 3), may help to reduce impact forces and joint loading and provide a strategy to reduce the incidence of impact related injuries that may stem from high volumes of repeated intense deceleration manoeuvres.
Deceleration Forces Encountered During Competitive Match Play
Following on from the data presented in the previous section, we would hypothesize that the highest mechanical loads that players are exposed to would also be associated with deceleration activities during competitive match play. Currently, to the authors knowledge only a small number of studies have investigated this within two major multi-directional team sports: 1) Basketball (Koyama et al., 2020, 2022; Nagano et al., 2021) and 2) Soccer (Dalen et al., 2016; Sasaki et al., 2021). In the study by Dalen et al. (2016) the mechanical forces (Player Load per meter) was measured across a three full-seasons of competitive home matches in elite male Norwegian soccer players (Rosenberg FC). Deceleration activities (> 2 m.s-2) were on average 28% higher than equivalent intensity accelerations and 65% higher than other match activities (figure 4).
In young footballers (age 10 ± 0.4 years) when comparing 24 different match activities, the top four activities that exposed young players to forces above 8G were all deceleration related:
- Braking heavily from a sprint = 35%
- Reducing speed gradually = 17%
- Stopping completely = 11%
- Preliminary step to adjust speed before braking = 7%
Similar findings have been reported in male and female basketball players (Koyama et al., 2020; Nagano et al., 2021). In the study by Koyama et al. (2020) who investigated the acceleration profile of high-intensity movements in top-level collegiate male basketball players, deceleration activities when performing on-ball and off-ball defence and when dribbling where in the top 7 movements registered above 6G forces (figure 5). When examining all cases above the highest 8G forces deceleration movements registered the highest number of cases (n = 135), representing almost a third (29%) of all movements above 8G forces. These findings were similar to Nagano et al. (2021) in female basketball players were deceleration movements also registered the highest number of cases (23%) above 8G.
Summary and Implications
- Current data that has examined the mechanical demands of braking when performing deceleration activity would suggest that this is the most mechanically demanding task a player will be exposed to in multi-directional sports.
- Accordingly, deceleration activities with high force characteristics are associated with high risk of muscle damage, soreness and fatigue (i.e., reduced force generating capacity) (Koyama et al., 2022) and the potential for overuse injuries if deceleration load is not carefully managed (Bowen et al., 2020; Caparrós et al., 2018).
- Given the high forces associated with deceleration and the potential for damage, heightened importance should be given to monitoring and preparing players for the demands of deceleration.
- Exposure to intense decelerations could provide a potential ‘vaccine’ to time loss injuries in multi-directional sport athletes. For example, unloaded players that have been exposed to a low volume of decelerations were at the highest risk of injury in professional male basketball players (Caparrós et al., 2018). Contrary to this, if players are exposed to sudden high volumes (spikes) of decelerations, this could also be particularly sensitive to development of overuse injuries (Bowen et al., 2020).
- For those working with youth athletes, monitoring exposure, and developing a young players deceleration ability could be particularly important in terms of reducing burden of overuse impact related injuries, growth related pain, and lower limb injuries in general.
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