Landing is a fundamental skill of many movements performed during netball. Given that running with ball in hand is a rule violation, players often perform leaps and bounds to evade opposition to receive a pass. These explosive jumps combined with abrupt landing decelerations impose hazardously high ground reaction forces (GRFs) on the lower body (24). As such, these GRFs coupled with incorrect landing technique have been suggested as a primary cause of lower-body injuries among female netball players (11,29,33).
A number of studies have investigated factors that influence the magnitude of landing forces. Notably, drop height (2,8,19,22,26), jumping distance (5,27,28), and the particular skills being performed (3,21,32) provide varying degrees of impact on GRF during landing. These factors can also potentially dictate the landing technique adopted by influencing knee angle (4–6) and foot placement (14,21) depending on the landing strategy used. The literature suggests that adopting fundamental landing mechanics supplemented with appropriate training strategies may help to minimize injury occurrence and enhance landing performance.
In light of this information, a logical step is to develop an understanding of the components that influence landing forces within netball. This article first explores the movement patterns within netball and the typical GRFs associated with various netball landings. A template of factors that may influence subsequent GRF while performing a successful landing ensues, and finally, an overview of an “ideal” landing sequence is provided along with identified training strategies to enhance landing proficiency.
NETBALL MOVEMENT PATTERNS
Despite netball's international popularity, there is a paucity of research identifying different patterns of landing movements with methodical consistency. A few studies that have attempted to quantify specific movements have used time-motion analysis to establish patterns, such as walking, jogging, and rest periods (23,34), whereas other studies have captured a comparatively limited sample of landing characteristics during match play (12,16,30).
Lavipour (16) event coded 2 premier league netball games during match play with reference to jump-landing performance. All players were investigated during the 2 games representing 4 teams, 28 players, and 7 different player positions. Players' jump movement patterns were coded as vertical, forward, or lateral in terms of direction as well as unilateral or bilateral in terms of the landing strategy. A summary of the results from this analysis is shown in Table 1.
The average number of jump-landings recorded across all positions was 58 per game, which equated to approximately 1 jump per minute (16). From a total of 416 analyzed jump-landings, on average 42% were forward, 32% were vertical, and 26% were classed as laterally dominant, per game. Despite similar jump-landing totals, Hopper et al. (12) reported 11, 50, and 38% for forward, vertical, and laterally dominated jump-landings, respectively. In addition, 1% of jumps were classified as backwards; however, this movement was not reported in Lavipour's analysis.
Interestingly, with respect to landing type, regardless of jump-landing movement differentiation, both Hopper et al. (12) and Lavipour (16) reported that players landed unilaterally 65% and bilaterally 35% of the time (collectively). In addition, the defensive positions were significantly less likely to land on both feet (14%) as opposed to unilaterally (86%) when compared with mid-court and attacking players who landed bilaterally (44%) (12). Furthermore, jumps in the vertical direction showed an equal number of unilateral and bilateral landings as opposed to a unilateral landing tendency for jumps in the forward and lateral directions (12,16).
Lavipour's study (16) also investigated jump-landings with a 180-degree turn mid-flight along with landings that were immediately followed by another jump or explosive movement. The majority of jumps analyzed did not turn while in-flight except for the wing attack position, reporting a turn 66% of the time. Performing a subsequent jump after landing was more prevalent among attacking positions (32%), as opposed to defense positions (16%). It was proposed that jumps with turns mid-flight were indicative of attacking play (16).
In summary, from the limited research on specific jump-landing characteristics witnessed during match play, different directions and jump-landing types are associated with positional demands. Despite the inconsistent findings, it should be noted that jump-landings are influenced by the inclusion of a ball, technical skill, and the style of play. It is apparent that all players are exposed to each landing situation, although each position demands varying degrees of jump-landing styles and strategies.
GROUND REACTION FORCES IN NETBALL
Although the action of landing remains similar for various sporting codes, how the body reacts to the landing can significantly differ. Athletes can develop specific adaptations within the body because of the demands of the activity or stresses they are subjected to (20). Therefore, it is important to review netball-related GRF research to gain an insight into the potential stresses that are encountered during netball performance (Table 2). The resultant GRF may be expressed as vertical (VGRF), horizontal (HGRF), and lateral (LGRF).
Steele and Milburn (30) investigated the effects of 4 different types of footwear and the GRFs produced by landing on 1 foot after performing a classic netball-attacking maneuver. The 15 elite netball athletes produced GRF ranges of 3.9–4.3 times their body weight (BW) for VGRF and 4.2–4.6 BW for HGRF. The authors concluded that reducing GRF is more effective through alterations in landing mechanics as opposed to the specific shoe worn. Furthermore, this study only used center position players; therefore, the GRFs associated with other positions/movement patterns were not identified.
A follow-on study by Steele and Milburn (31) examined the influence of 12 different synthetic sport surfaces on GRFs on netball landing. Ten skilled netball players performed an attacking movement involving acceleration from a standing position, an abrupt stop onto a force platform, receiving a pass, and then off-loading the ball to another player. For all 12 surface conditions, the mean peak VGRF and HGRF across all subjects for dominant foot landings were 3.8 and 3.4 BW, respectively.
Another study using match-specific maneuvers compared the GRF produced by either a forefoot or heel dominated landing (29). The classification of the landing was determined by post hoc analysis of the landing examining the center of pressure data. Ten competent netball players performed a standard netball-attacking task where they had to catch a high pass. The entire movement included running forward, evading a defender, leaping to receive a pass, and then landing on their dominant leg. Mean peak VGRF for the heel and forefoot patterns during single-leg landing conditions were 5.3 and 5.7 BW while HGRF were recorded at 3.3 and 2.0 BW.
Hopper et al. (13) investigated 15 elite-level netball players executing a forward jump onto a force plate. Each subject was instructed to land on his/her dominant foot only. The distance jumped was calculated to be 1.25 times the subject's leg length, which was representative of a typical distance that a player may jump during a netball game, based on pilot testing. Mean peak VGRF of 3.3 BW was reported.
One comparative research study investigated the GRF of various netball landings (24). The purpose of the study was to establish whether an extra step on landing would significantly alter the forces acting on the body. The data were compiled using 18 netball players completing 5 different landing conditions at 2 pass heights, either above the head or the shoulder height. Peak VGRF across the 5 different landing conditions ranged from 3.5 to 5.7 BW, whereas the HGRFs ranged from 0.8 to 1.8 BW.
In summary, on landing the body is exposed to substantial vertical and horizontal GRFs. The vertical component appears the larger of the 2 forces, with mean peak values of 5.7 BW compared with 4.6 BW for HGRF. Also apparent is that netball-specific research quantifying the GRFs associated with bilateral landings is scarce, with the majority of the studies incorporating single-leg dominant foot landings. Depending on landing condition, and with an average of approximately 60 powerful jump-landing movements per game (16), a typical netball player can experience an enormous accumulative load through the lower extremities. In addition to this load are the impact forces accumulated with walking, jogging, and running between jump movements, which are indicative of natural play.
FACTORS THAT INFLUENCE LANDING KINETICS
Influential factors identified in the literature include drop height, as this can impact on landing velocity; jump distance, which dictates angular momentum; and landing strategy, as landing with 1 or 2 feet requires differing muscular recruitment patterns and balance strategies. Auxiliary factors such as foot placement, knee angle during initial ground contact, and the particular netball skill being performed during landing have also been shown to contribute a significant influence on GRF during landing.
The relationship between drop height and GRF on landing is well documented. Caster (2) investigated the effects of increasing drop height on landing kinetics during bilateral drop landings. VGRF ranges of 3.89–6.62 BW were reported with the authors concluding that impact forces were found to increase with height. Research with similar drop heights examined muscle activation patterns and subsequent VGRF in female volleyball players during drop jumps (8). These authors observed significant overall increases in VGRF of 49.0% ranging from 1.53 to 2.28 BW as a direct result of increasing the height of the jump.
Research from Makaruk and Sacewicz (19) investigated the effects of increasing drop height on landing impact during bilateral drop jumps. A significant increase in VGRF (p < 0.01) as a result of increasing height was reported observing VGRFs of 4.5, 5.8, and 6.5 BW for 20, 40, and 60 cm height, respectively. Slightly lower VGRF ranges of 2.00–3.78 BW were derived during drop landings from the same height increments among physically active males and females (26). However, in contrast to the findings of Makaruk and Sacewicz (19), Peng (26) observed that VGRF produced from 60 cm height was not significantly different compared with the 40 cm height.
To the author's knowledge, only 1 study has investigated the effects of differing heights on all force components (22). Using bilateral drop landings from heights of 32, 52, and 72 cm GRFs ranged from 3.09 to 5.26 BW for VGRF, 0.62 to 1.08 BW for HGRF, and 0.34 to 0.45 BW for LGRF. It was found that only VGRF and HGRF indicated significant differences across all 3 heights (p < 0.05).
The effects of incremental jump distance on GRF have not received the same attention in the literature as drop height. Simpson and Cronin (28) used a unilateral horizontal jump and explored propulsive GRF production from jump distances of 80, 120, and 160% of subject's leg length. An increase in distance had a minimum effect on the landing forces, with GRF ranging from 2.4 to 2.7 BW for VGRF and 0.6 to 0.7 BW for HGRF. It was interesting to note that the lowest HGRF was generated from the furthest distance (160% leg length) and the greatest HGRF originated from the closest distance. It was assumed that this was as a result of the landing technique adopted as the distance increased.
Another study investigating the effects of increasing jump distance on lower-body kinetics explored jumps at 30, 60 and 90% of subject's leg length (27). The horizontal jumps in their study from the 6 female subjects equated to average distances of 43, 86, and 129 cm. These authors observed force ranges of 1.38–2.78 BW for VGRF and 0.21–0.98 BW for HGRF. HGRF indicated significant differences across all 3 heights (p < 0.05); however, only distance between 30 and 90% were found to be significant for VGRF.
Research from Dufek and Bates (5) set out to develop a predictive template for impact landing forces through the use of various regression models. Jump distances of 40, 70, and 100 cm reported 4.11, 4.36, and 4.51 BW during bilateral landings with varying degrees of knee flexion. This equated to a total increase of 9.7% across all distances, concluding that impact forces were found to increase with distance.
A multitude of landing strategies are possible within netball (12,16). These range from landing with 1 or 2 feet, having to land from various directions, and deciding on a mixture of force absorption/dissipation strategies. This can be classed as the type of footfall patterns used along with the degree of knee and hip flexion present during foot contact.
Bilateral versus unilateral
Although it is well documented that injuries can occur during bilateral landings, the general consensus is that landing unilaterally carries more vulnerability to injury (18,25,35). This generalization stems from the fact that unilateral landings have a decreased base of support, which reduces stability and potentially increases muscle activation, creating a more abrupt landing (35).
The kinematics and kinetics between bilateral and unilateral landings were explored by Weinhandl et al. (35). It was observed that unilateral landing compared with bilateral landing increase VGRF by 44% along with an increase in total energy absorption of 11%. In agreement with the previous study, Pappas et al. (25) observed an 18.8% increase in VGRF from unilateral drop landings in comparison to bilateral at a height of 40 cm.
Both studies (25,35) concluded that unilateral landings were accompanied by larger joint angles on impact. It is speculated that insufficient levels of leg strength are responsible for greater joint angles (17). Lephart et al. (17) observed that females who increased leg strength through resistance training significantly decreased initial hip and peak knee angle during landing, thus adopting a mechanically more efficient landing style, congruent with lower landing forces.
Foot placement is also referred to as a footfall pattern. Landing with the heel foot as opposed to the forefoot seemed to be the preferred style of landing among netball players (30,31), although this can become problematic as heel landings have the potential to generate larger GRFs. Netball players have been reported to produce significantly greater VGRF during heel landings compared with forefoot (7.3 versus 2.7 BW) while receiving a pass at chest height (21). These findings were supported by Kovacs et al. (14) concluding the heel landings produced 3.4 times greater peak VGRFs compared with forefoot landings from a 40 cm drop height.
In contrast, Steele and Lafortune (29) reported no significant differences in VGRF between heel foot (5.3 BW) and forefoot (5.7 BW) landings during a typical single-leg netball maneuver. However, HGRF produced by forefoot landings in this same study were 39.4% lower compared with heel landings. Steele (32) also reported that foot placement was influenced by the particular pass type received. Subjects receiving a high pass had a tendency to land in a forefoot position, as opposed to a heel foot placement. Hopper et al. (12) agreed reporting 88% forefoot landing occurring from an overhead pass as opposed to 62% from chest height and 26% from below waist pass height.
Despite the research trends, footfall patterns within netball are often dependent on the activity being performed before landing and the subsequent maneuver being executed. If the aim is to decelerate the body as fast as possible, then heel landings would prove superior with respect to halting horizontal momentum in contrast to forefoot landing.
The amount of knee flexion present during landing determines either stiff or soft landing characterization (4–6). Devita and Skelly (4) have classified knee angles during landing of greater than 90° as stiff landings, and smaller than 90° as soft landings. Research from Dufet and Bates (5) further categorized landings into 3 varying degrees of stiffness; angles less than 75° as fully flexed (FF) between 110° and 75° as slightly stiff (SL) and greater than 110° as stiff (ST).
Dufek and Bates (5) assessed the dynamic loading of height, distance, and knee angle during bilateral landings. It was observed that an increase in knee angle significantly increased VGRF reporting 3.6, 4.0, and 5.4 BW for FF, SL, and ST knee angles. This was also supported by Devita and Skelly (4), who reported that 23% larger forces occurred during stiff landings as opposed to soft landings. It was also observed that the hip and knee muscular structures absorbed 19% more kinetic energy during the soft landings, illustrating how landing technique has the potential to decrease impact forces through selective GRF dissipation (4).
Specific netball skills such as catching a pass can place the body in vulnerable positions, which can negatively affect the force attenuation capabilities of the lower extremities. Cowling and Steele (3) observed that the act of catching a ball at chest height while in-flight has the potential to alter the kinematics of the hip and trunk. This is supported by research from Steele (32) who explored the effect of pass height on GRF among netball players. Subjects were required to land on a force plate after receiving either a pass at chest height or at heights above the head. It was noted that delivering a higher pass, the receiver reduced their HGRF on landing by 13.0% from 3.1 to 2.7 BW; however, this led to an increase in VGRF of 20.0% from 4.5 to 5.4 BW. These findings were supported by Neal and Sydney-Smith (21) reporting an average HGRF of 2.5 BW for chest height passes and 1.9 BW for passes above head height.
In summary (Table 3), there seems little doubt that jump height and distance has a marked effect on landing GRF. Athletes who jump higher or drop from a higher point will potentially experience greater impact forces because of the effect of gravity and associated velocity on impact. With respect to jump distance, greater propulsive forces on take off must be applied to achieve further distance (7). This effectively increases both vertical and horizontal center of mass velocity, thus acting in the same fashion as the effect of height. Unilateral landings are associated with larger hip and knee angles on initial ground contact. The suggested cause is a deficiency in lower-body strength as larger angles require less muscular force to maintain due to smaller joint moments. Larger knee angles imply that the forces are transferred and absorbed by the passive structures, which may create a more susceptible environment for lower-body injury (5). Regarding foot placement, landing in a forefoot to heel pattern allows the body to absorb forces over a longer period of time. This may help to decrease the musculoskeletal stress present on impact. Finally, by attempting to receive an above head pass, the body has converted horizontal momentum into vertical propulsion to initiate a vertical jump to catch the ball. This process supports GRF reductions by adopting a more suitable position to increase knee flexion and initiate forefoot landings (15).
FUNDAMENTAL LANDING PRINCIPLES
The aforementioned described netball performance involves a variety of jump-landing sequences, which are often reliant on opposition movement and allocated court space. It is also apparent that a diverse range of factors, including aspects that are outside the control of the athlete can influence landing forces. Consequently, it is misleading to talk of developing a perfect landing model. A more appropriate strategy is to articulate a set of fundamental landing principles (Table 4), which can be applied to the diverse landing conditions performed throughout competition.
Essentially, a successful landing decelerates the body's projected momentum under control while avoiding injury (4). Steele and Lafortune (29) explored the relationship between kinematic factors and landing GRF while performing a common attacking movement in netball. Using 3-dimensional cinematography, they correlated certain landing movements with GRF recordings to create a set of suggested landing fundamentals. It is proposed that an effective landing displays adequate flexion of the hips, knees, and ankles (Figure) as this helps to dissipate the majority of the energy (29). Absorbing the impact forces over a greater time period reduces the sudden effects of landing by subtly lowering the body's center of mass. Also the chest is encouraged to be above knees with shoulders and hips aligned. In addition, knees should avoid excessive adduction or abduction as equal distribution of impact forces across both the medial and lateral compartments of the knee may reduce the impact stress (10). With respect to foot placement, a forefoot to heel ground contact pattern is advocated as this helps to disperse forces more evenly throughout the foot (14). This pattern also acts like a shock absorber for the leg. Adopting these fundamental landing principles may help to reduce both the rate and magnitude of GRF during impact.
Although the concept of soft landings is ideal for attenuating impact forces, they may become detrimental toward performance. Deliberately absorbing landing forces through increased ranges of joint flexion slows down the execution of subsequent movements. This is due to the fact that, in netball, landings are often met by additional jumps, which require the leg to be somewhat extended on landing (16). A logical approach is to implement the appropriate training strategies to enhance performance by increasing the lower body's ability to withstand greater impacts.
Research suggests that a combination of training components has the most advantageous effect on reducing landing force as well as conditioning the body to effectively withstand these repetitive impacts. The 4 most promising components appear to be (a) teaching correct landing fundamental principles, landing mechanics, and force dissipation strategies; (b) improving balance and dynamic stability, specifically surrounding the ankle and hip joint; (c) increasing muscular strength through resistance training, particularly the muscles of the posterior chain; and (d) heightening neural drive through plyometric type exercises, as this can strengthen specific muscle recruitment and synchronicity aiding the skill of landing. For the reader's reference, the following review articles (1,9) provide an in-depth discussion on each of the identified training strategies with specifics on intervention details.
To promote fundamental landing training, progressively overloading landing intensity is advocated. Through systematic progression of task specific intensity, the body has the ability to effectively adapt to the stresses experienced during netball match play. These progressions in task difficulty are not solely for injury prevention, as the concept of load intensification supports the notion of enhanced transfer to on-court performance, thus bridging the gap between training and competition.
CONCLUSION AND PRACTICAL APPLICATION
It is widely acknowledged that research has quantified the GRFs surrounding typical netball movements and maneuvers involving landing. This article was designed in an effort to develop an understanding of the components that impact on landing forces during landing. Evidently, these forces are associated with lower-body injury occurrence through sudden force application along with accumulative impacts, which are indicative of natural play. Based on a fundamental understanding of landing biomechanics and a review of observed research, a number of jump-landing kinetic modifiers have been detailed. Accepting that landing is a multifaceted task, it is essential to acknowledge the identified modifiers during landing performance.
It is important to remember that it is unrealistic to execute perfect jump-landing form every time during a game. Implementing fundamental landing principles may help to reduce injury in both an acute and chronic sense. This is achieved by effectively dissipating the impact forces through the appropriate structures of the body. In addition, selective strength and conditioning strategies may help to provide the best platform to prepare athletes for landing activities during competition. Future research may want to explore GRFs in all 3 planes of motion during landing tasks relevant to netball that progress in intensity.
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