In a recent blog we highlighted the importance of strength qualities for change of direction largely from a performance perspective. Change of direction actions are of course associated with numerous musculoskeletal injuries including the anterior cruciate ligament (ACL) rupture, lateral ankle sprains, hamstring strains, groin pain and hip adductor strains. Therefore, a holistic approach to technical and physical preparation is required to not only improve change of direction performance but to mitigate change of direction specific injury. This article outlines considerations for injury risk mitigation for change of direction with specific focus on physical qualities. Our physical preparation for change of direction model (Dos’Santos & Jones, 2022) is presented with implications for training.
‘The Problem’
Directional changes, particularly side-step cutting manoeuvres, are common actions involved in non-contact ACL injuries in handball (Olsen et al., 2004), soccer (Faude et al., 2005; Brophy et al., 2015; Walden et al., 2015; Lurcano et al., 2021), rugby union (Montgomery et al., 2018) and American football (Johnstone et al., 2018) due to the propensity to generate high knee joint loads (e.g., knee abduction and rotation moments and anterior shear forces) (McLean et al., 2003; McLean et al., 2004) during the ‘’plant’’ (final foot contact) step of the manoeuvre that increase ACL strain (Shin et al., 2009; 2011). In addition, changing direction has also been identified as an action associated with lateral ankle sprains (Fong et al., 2009), adductor strain injuries (Serner et al., 2019), hamstring strain injuries (Kerin et al., 2022; Gronwald et al., 2022) and development of athletic groin pain (Franklyn-Miller et al., 2017). Musculoskeletal injuries like these represents a failure of the tissue to tolerate the mechanical loads applied to it. Of course, there are a multitude of factors responsible as to why a tissue may succumb to that load at that specific moment in time (e.g., poor movement strategy, fatigue, perturbation, poor conditioning, etc.). From a practical perspective, strategies to reduce loading (e.g., ensure good movement quality) and/ or prepare the tissues to tolerate such tissues loads (e.g., through training and load management) are essential objectives for injury mitigation. Hence, developing safer change of direction techniques (to reduce load) and the physical capacity (to tolerate load) to perform change of direction manoeuvres is therefore an important prerequisite not only for performance, but for injury mitigation to maximise player welfare and availability.
The short- and long-term consequences of ACL injury has led to widespread research interest pertaining to change of direction biomechanics with a view to reducing knee joint loads during such manoeuvres to better inform injury mitigation interventions. A range of intervention strategies to address hazardous change of direction mechanics (knee joint loads) have been investigated in the literature including technique modification, multi-component training (e.g., balance with technique training, or resistance training with plyometrics, balance and trunk training), time-saving neuromuscular warm-ups, trunk control training and perturbation-enhanced plyometric training (for more details see our scoping review Dos’Santos et al., 2019a). Based on this review and subsequent studies (Dos’Santos et al., 2019b; 2021a), technique modification programmes have generally been shown to be effective at lowering knee joint loads (e.g., lower knee abduction moments) during change of direction manoeuvres. Other abovementioned training methods which tend to focus on developing physical qualities (e.g., strength, trunk stability, balance) show contrasting evidence as to whether multiplanar knee joint moments reduce, increase, or do not change at all (Dos’Santos et al., 2019a), and therefore, maybe viewed as questionable strategies for specifically addressing change of direction mechanics (i.e., lowering knee joint loads). However, it should be noted that such ‘physical’ training methods MUST be adopted given the performance – injury conflict and that athletes need conditioning to tolerate the high loads achieved during change of direction (McBurnie et al., 2021). Particularly given that through technique modification or speed & agility training methods athletes may become faster (linearly); thus, approach directional changes with more momentum and therefore, need to be able to handle the greater loads experienced at the lower limb joints to execute such manoeuvres safely and effectively.
A Model for ‘Safer’ Side-step Cutting Whilst Recognising the Impact on Performance
FIGURE 1 provides a model of technique for safer side-step cutting (60-110°) and considers the implications for performance (e.g., performance-injury conflict). The Cutting Movement Assessment Score (Jones et al., 2017; Dos’Santos et al., 2019c; Dos’Santos, et al., 2021b) provides an avenue to evaluate against this model in the field. Essentially, during directional changes such as side-step cutting the aim is to achieve high exit velocity and / or moderate to large deflections/ directional changes of the centre mass (CM) to help evade an opponent. In side-step cutting, the former maybe influenced by the approach velocity (McBurnie et al., 2021; Jones et al., 2022); both the velocity of approach and angle of direction change dictate the intensity of the directional change (e.g., ground reactions forces [GRFs]) and subsequent knee joint loads experienced (Dos’Santos et al., 2018). To enable this without evoking repetitive high loads on the knee joint, then prior braking and anticipatory postural adjustments during the penultimate foot contact (Jones et al., 2016) or earlier (Dos’Santos et al., 2021d) is required. Greater penultimate foot contact braking (e.g., touchdown distance (foot to CM distance)), rearward trunk lean, shorter steps with large reductions in flight time and greater knee and hip flexion) helps lower the GRFs experienced and avoid a ‘heel contact’ at touchdown (David et al., 2017; Donnelly et al., 2017), which subsequently lowers knee joint loads experienced during final foot contact.
The postures adopted at touchdown of the final foot contact influence the multi-planar loads experienced at the knee (FIGURE 1). Postures associated with peak knee abduction moments include: lateral trunk flexion (Dempsey et al., 2007; Jones et al., 2015), markers of lateral leg plant (e.g., lateral leg plant distance, step width, initial hip abduction) (Kristianslund et al., 2014; Jones et al., 2015; Havens & Sigward, 2015), initial knee abduction (McLean et al., 2004; Kristianslund et al., 2014; Jones et al., 2015) and flexion (Robinson et al., 2015; Weir et al., 2019), hip internal rotation (Sigward & Powers 2007; Havens & Sigward, 2015), and internal foot progression angle (Sigward & Powers, 2007) all of which lead to a more medially positioned knee relative to the GRF vector in the frontal plane. Reduced hip and knee flexion during final foot contact of side-step cutting has also been shown to be associated with greater loads (Dos’Santos et al., 2021c). The majority of these can be addressed to lower knee joint loads experienced and do not affect performance (e.g., task completion time, exit velocity). However, lateral trunk flexion may have performance implications to help deceive an opponent during attacking agility scenarios (i.e., dropping the shoulder), but generally speaking leads to slower performance and greater knee joint loads (Dos’Santos et al., 2021c) and thus, should be discouraged. Narrowing lateral leg plant distance may help reduce knee joint loads but may also compromise the production of medially directed impulse for the required directional change and to increase exit velocity (Jones et al., 2015). Furthermore, encouraging more lower limb flexion (hip & knee) during final foot contact will help reduce GRFs and subsequent knee joint loads but would prolong ground contact time and may lead to slower performance (Dos’Santos et al., 2021c). Therefore, the performance-injury conflict associated with these later variables has implications for physical preparation (e.g., develop muscular support structures) for athletes/ players for injury mitigation to avoid ‘positions of no return’ during change of direction actions.
Physical Preparation Model of Change of Direction
As mentioned earlier physical preparation is going to be important to allow the player to tolerate those large knee joint and tissue loads experienced during change of direction manoeuvres. FIGURE 2 originally presented at keynote presentations in recent years (Jones, 2019, 2021) and in Dos’Santos & Jones (2022), highlights key areas to focus on regarding knee and ankle joint injury mitigation. The model is based on what is required from a neuromuscular perspective to prevent undesired mechanics (such as some of those mentioned in FIGURE 1) and identifying knee and non-knee spanning muscles that can oppose and support undesired mechanical loads at the knee and ankle. The remainder of this section explains the model.
Dynamic Trunk Control
The trunk contains approximately half of the body’s mass which must be supported on one limb during side-step cutting. As explained in the previous section, lateral trunk flexion increases frontal plane moment arm distance as the GRF vector orientation shifts more lateral from the knee joint of the ‘plant’ leg, thus, increasing knee joint moments (abduction & internal rotation) during side-step cutting (Dempsey et al., 2007; Hewett & Myer 2011; Donnelly et al., 2012). Whilst lateral trunk flexion maybe a movement that helps deceive a defender during an ‘offensive’ side-step cutting manoeuvre, findings from Sankey et al., (2020) suggest that lateral trunk flexion might be due to frontal plane hip acceleration to regain control of the CM during unanticipated side-step cutting. Thus, essentially such a movement strategy maybe indicative of an inability to control the trunk during the manoeuvre (FIGURE 3). Additionally, deficits in dynamic trunk control and core proprioception have found to be associated with ACL injury incidence in female athletes (Zazulak et al., 2007a; Zazulak et al., 2007b). Hence, the ability to control the trunk during multidirectional speed actions is essential to prevent generating high knee joint loads that the ACL and other structures must sustain.
Pelvic Control
External Hip Rotator (gluteal) Strength and Activation
Based on musculoskeletal modelling hip muscles namely the glute medius, maximus, and piriformis (Maniar et al., 2018; Maniar et al., 2020; Maniar et al., 2022) oppose knee abduction and rotator moments during side-step cutting. These findings coincide with findings from prospective studies that have found that deficits in isometric external rotation and abduction strength have been found to be associated with the incidence of non-contact ACL injuries (Khayambashi et al., 2016). Gluteal strength (hip extensor) will also be required to support large hip flexion moments during penultimate and final foot contact (Jones et al, 2016; Dos’Santos et al., 2019d) and to facilitate effective propulsion (Maniar et al., 2019).
Hamstring and Soleus Strength and Activation
Research conducted by Maniar et al. (2018 & 2019) using musculoskeletal (MSK) modelling found that the hamstrings were the primary muscle group to oppose anterior tibial shear forces at the knee during side-step cutting. In support of this, Weinhandl et al. (2014) found that reduced hamstring strength due to acute fatigue increased ACL loading via MSK modelling of a side-step cutting manoeuvre. Maniar et al. (2018 & 2019) also found the soleus was another muscle that helped oppose anterior tibial shear forces at the knee during side-step cutting manoeuvres and this observation has also been confirmed in other studies involving single leg landing (Prodaza & White, 2010; Mokhtarzadeh et al., 2013). Therefore, focused strengthening of the hamstrings and soleus is a consideration to help with knee joint stability during change of direction and deceleration manoeuvres.
Whilst not directly associated with opposing knee joint loads, eccentric quadriceps strength is essential to facilitate effective braking (Jones et al., 2017; Maniar et al., 2019; Jones et al., 2022; Mateus et al., 2020) and support large knee flexor moments created during weight acceptance of penultimate and final foot contact (Jones et al., 2016; Dos’Santos et al., 2019d). Moreover, weak eccentric quadriceps may result in a braking strategy with minimal knee flexion and increased hip and trunk flexion (FIGURE 4) resulting in high eccentric loads placed on the hamstrings elevating the risk of hamstring strain injury (Warrener et al., 2021; Mateus et al., 2020). Thus, the model advocates the development of eccentric quadriceps strength along with hamstring strength exercises to mitigate hamstring strain injury risk during deceleration and change of direction manoeuvres.
Peroneus longus and tibialis anterior activation may help with ankle joint stability to control inversion, supination, and internal rotation (Konradsen & Ravn, 1991; Neptune et al., 1999; Fong et al., 2009) and mitigate the chance for lateral ankle sprains during change of direction manoeuvres.FIGURE 2 also considers recent research that has highlighted intrinsic foot and toe flexor strength may also be beneficial for performance and ankle stability during change of direction. For instance, intrinsic foot muscles contribute to elastic energy storage and return (Kelly et al., 2019), support medial longitudinal arch (McKeon et al., 2015; Tourillon et al., 2019), facilitate energy absorption and facilitate propulsion (Yuasa et al., 2018; Tourillon et al., 2019), and ankle stability (Fraser et al., 2016). For exercise suggestions the interested reader should see the article by Tourillon et al. (2019).
Training Implications
Trunk and Pelvic Control
Exercise suggestions aligned to target areas for COD in relation to knee injury mitigation are summarised in FIGURE 5. Trunk training could begin with static trunk exercises (e.g., planks, side planks, rollouts, etc.) and progress to multi-joint unilateral (to challenge dynamic control of the trunk) strength exercises (Whyte et al., 2018). Balance training (6 weeks, 4 ×/wk.) has shown to increase trunk and proximal hip muscle activation along with reduced external knee abduction moment (Olivera et al., 2017) during perturbed side-step cutting manoeuvres. Balance training has also been shown to increase hamstring co-contraction (Cochrane et al., 2006) and lower knee abduction and internal rotation moments (Cochrane et al., 2010) during side-step cutting. Using overhead running (e.g., A and B drills, overhead walking lunge) and change of direction drills with arms over head or carrying a medicine ball overhead encourage ‘tall’ posture while sprinting and increase height of CM during changes of direction to challenge neuromuscular control of the trunk, respectively. These drills were used by King et al. (2018) in their technique modification study which were shown to be effective to develop inter-segmental control between the trunk and pelvis to address athletic groin pain in athletes. To further develop pelvic control, hip-hike exercises could be used to improve pelvic control at a local level before progressing to unilateral strength and multidirectional plyometrics to develop trunk and pelvic control at a global level. The abovementioned, overhead running and COD drills could be integrated into field/ pitch-based training to further enhance intersegmental control between trunk and pelvis (King et al., 2018).
Targeting Knee and Non-knee Spanning Muscles to Oppose Mechanical Loads on the Knee
A similar approach may be used to target key hip musculature (glute med, maximus, minimus and piriformis) through isolated isometric and concentric resisted abduction, external rotation, and extension (e.g., clams, cable hip abduction, band sidewalks, hip hike, etc.) to supplement multi-joint, unilateral strength exercises. Given the important role of the hamstrings in opposing anterior tibial shear forces during landing and change of direction manoeuvres (Maniar et al., 2018; 2022), hamstring conditioning is essential for knee injury risk mitigation. Furthermore, given the susceptibility of the hamstrings to strain from sprint, deceleration and change of direction actions (Kerin et al., 2022; Gronwald et al., 2022), only heightens the need for hamstring strength development. Both low and high velocity hip and knee dominant hamstring exercises should be considered (see videos in previous Blog for examples). There is a suggestion due to differing attachment sites and moment arm lengths about the knee of each hamstring muscle in the frontal and transverse plane may influence each muscle’s ability to oppose loads within these planes (e.g., abduction and internal rotation) (Maniar et al., 2022). For instance, the medial hamstrings (semitendinosus / semimembranosus) may oppose knee abduction/ valgus moments, whereas the lateral hamstrings (Biceps femoris short and long head) contribute to abduction/ valgus loading (Maniar et al., 2018, 2019, 2022). Although these roles appear insignificant in relation to the gluteus medius (Maniar et al., 2018, 2019). The biceps femoris has the potential to help oppose knee internal rotation moments and due to a greater cross-sectional area than medial hamstrings muscles suggest a greater relative importance of the biceps femoris (Maniar et al., 2022). In addition, given the greater prevalence of the biceps femoris long head for hamstring strain injury (Woods et al., 2004) in relation to the medial hamstring muscles highlights the necessity to target this specific hamstring muscle through training. Whilst Nordic hamstring lowers (NHL) result in greater eccentric EMG amplitude of the biceps femoris than many other hamstring focused exercises (Bourne et al. 2017a), the greater ratio of lateral to medial hamstring activation (Bourne et al. 2017a), greater hypertrophic response (% change in volume and muscle cross-sectional area) from training with 45° hip extension vs. NHL (Bourne et al. 2017b) and the greater metabolic activity (ratio of biceps femoris long head to semitendinosus percentage change in T2 relaxation time) of the biceps femoris long head from 45° hip extension exercise compared to NHL (Bourne et al., 2017a; Bourne et al., 2018) suggests hip dominated exercises (e.g., Uni- and bilateral; Romanian deadlift, 45° hip extension, etc.), must be included in the programme to specifically target the biceps femoris long head. Finally, based on the physical preparation model proposed (FIGURE 2), although secondary to the hamstrings in opposing anterior tibial shear force, the soleus (Maniar et al., 2022) should be targeted. Whilst isolating the soleus from the gastrocnemius within exercises is difficult, utilising seated calf-raises (i.e., concentric, isometric and eccentric variations) as an assistance exercise within programmes with appropriate progressions in intensity (load) should provide adequate isolation of this muscle for knee injury mitigation.
Other Considerations
Whilst in vivo, in vitro and in silico studies tend to show the quadriceps as an antagonist to the ACL, increasing anterior shear force particularly at low knee flexion angles (Maniar et al., 2022), eccentric quadriceps strength development is essential to facilitate effective braking (Jones et al., 2017; Jones et al., 2022) and support large knee flexor moments created during weight acceptance of penultimate and final foot contacts (Jones et al., 2016). Furthermore, as highlight in FIGURE 4 poor eccentric quadriceps strength could lead to undesirable braking postures that could increase hamstring strain risk (Warrender et al., 2021; Kerin et al., 2022). Development of eccentric strength in should begin with low-velocity eccentric exercise (e.g., back squats using weight releasers to accentuate the eccentric phase) to higher velocity eccentric exercises (e.g., bilateral or unilateral loaded drop landings, deceleration drills, etc.) (see recent Blog for example videos). For a detailed outline of eccentric training options see Harden et al., (2022). To target peroneus longus and tibialis anterior activation to enhance ankle stability for injury mitigation then balance training (e.g., single limb standing, squatting, and catching on stable and unstable surfaces perhaps within warm-ups) and placing the onus on unilateral versions of resistance and jump landing/ plyometric exercises within sessions should be considered.
Finally, as highlighted early on this article hip adductor (groin) muscle injuries are associated with side-step cutting manoeuvres (Franklyn-Miller et al., 2017; Serner et al., 2019). During the final 30% of the final foot contact (propulsion into intended direction of travel) as the hip and knee extends and hip is abducted and externally rotated (pelvis rotates into intended direction of travel), there is increased lengthening of the adductor longus coupled with increased activation (Dupre et al., 2021). In addition, the gracilis shows its fastest lengthening velocity and activation during the last quarter of final foot contact (Dupre et al., 2021). These conditions place a greater load on these muscles in a vulnerable lengthened position (eccentric load), highlighting the importance of flexibility and strength to prepare players for these repeated exposures during match play. Indeed, decreased strength in the hip adductor muscles has been prospectively linked to increased groin muscle injury in soccer players (Moreno-Perez et al., 2019; Markovic et al., 2020). Therefore, developing strength of the adductor muscles may help with the ability to tolerate the increased loads placed on these muscles during cutting and evidence suggests the Copenhagen adductor exercise maybe an additional exercise to consider to develop eccentric adductor strength to prepare multidirectional speed athletes for the demands of repeated high-intensity side-step cutting (Schaber et al., 2021).
Summary
Change of direction actions are associated with numerous musculoskeletal injuries including the anterior cruciate ligament ruptures, lateral ankle sprains, hamstring strains, groin pain and hip adductor strains. Furthermore, regarding the knee, the performance-injury conflict involved with change of direction manoeuvres presents a further challenge to practitioners to better prepare athletes for the demands of change of direction where much of the emphasis of training is on enhancing performance. A holistic approach to technical and physical preparation is required to both improve change of direction performance and mitigate change of direction specific injury. This article outlines our physical preparation for change of direction model focused on considerations for knee and ankle injury risk mitigation for change of direction actions, whilst also considering the ramifications for other common change of direction specific musculoskeletal injuries. The exercise suggestions provided based on this model provides ‘food for thought’ in designing and implementing physical preparation programmes for multidirectional speed athletes.
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