The Influence of Task Design when Assessing Landing Biomechanics Related to ACL Injury: A Study of Netball Players and Females Inexperienced at Landing

Tyler J Collings

doi:10.25907/00377

Background: Severe injuries in netball, such as rupture of the anterior cruciate ligament (ACL), typically occur during landing from a jump. Assessment of injury biomechanics relating to landing is frequently performed in a laboratory setting using a drop landing task. However, drop landing is substantially different to landings performed in a game, and therefore may not be an optimal test for measuring biomechanics in a way that is externally valid. One approach to enhancing a laboratory-based task to produce more externally valid data, is to incorporate more task characteristics that reflect those encountered in a game setting. As such, it is important to consider how changing task characteristics effects landing biomechanics. In addition, landing is a complex motor skill which requires careful coordination of the lower limb joints and muscles. Therefore, the skill of landing is likely developed with experience. However, the effect of skill on landing biomechanics is relatively unknown; particularly in the context of assessing injury risk. Aims: The first aim of this study was to determine if the inclusion of task representative characteristics would alter biomechanical variables related to ACL injury compared to the widely used drop landing task. The second aim was to compare landing biomechanics relating to ACL injury between high performance female netballers (netball group), and females who are inexperienced at landing (novice group). The third aim was to investigate the effect of a perturbed trunk position at landing on the magnitude of kinematic, and kinetic variables associated with ACL injury risk. Study Design: Cross-sectional cohort study Methods: Biomechanical data were collected from a group of 23 high performance female netball players (age: 17.5±1.7 years, height: 1.77±0.06 m, mass: 66.5±6.33 kg, netball experience: 8.5 ±2.3 years; netball group), and 23 active females who had minimal experience playing sports involving jump-landings (age: 22.0±3.2 years, height: 1.70±0.05 m, mass: 64.4±6.7 kg; novice group). Participants performed two bilateral landing tasks; (1) drop landing from a 40-cm high box (drop landing), and (2) landing following a jump to grab a ball suspended from the ceiling (ball landing). 3D lower limb joint angles, moments, ground reaction force (GRF), joint contribution to work, and joint angle variability were compared between the drop landing and ball landing tasks, as well as between netball and novice groups for both legs (defined as lead and trail, depending on how the participants chose to perform the drop landing). Time series data were compared for statistical differences using the 95% confidence interval of the mean difference, while statistical equivalence was also tested using equivalence testing (bounds set at d = 0.5). Discrete time point data were compared for statistical differences using a linear mixed model for main effects of task, group, and interaction effects (α < .05). Results: Compared to ball landings, drop landings demonstrated similar joint angles and moments, but elicited significantly greater peak vertical GRF (lead leg, MΔ = 0.6± BW; trail leg, MΔ = 0.3 BW), and average loading rate (lead leg, MΔ = 12.4 BW/s; trail leg, MΔ = 7.6 BW/s). A comparison of between leg symmetry during drop landings indicated significantly less sagittal plane ankle (MΔ = -4°), knee (MΔ = -4°), and hip angles (MΔ = -2°) in the lead leg at initial ground contact compared to the trail leg. This between leg asymmetry was not apparent in the ball landings. In addition, participants were exposed to significantly greater absolute peak vertical GRFs (MΔ = 0.21 BW), and average loading rates (MΔ = 5.25 BW/s) during the drop landings compared to the ball landings. Despite displaying only small, short increases in knee and hip extension moments at initial ground contact of the drop landings, participants in the netball group had significantly greater ankle plantar flexion moments during the entire loading phase of landing when compared to ball landings. A comparison between netball and novice groups revealed that the participants in the netball group produced greater relative work at the hip (MΔ = 3%J/kg.m), and less relative work at the knee (MΔ = -7%J/kg.m) during the landing phase of both drop and ball landings. Furthermore, they exhibited smaller values for key variables previously associated with ACL injury such as lead knee abduction moment (MΔ = -0.15 Nm/kg.m), peak vertical GRF (lead, MΔ = -0.42 BW; trail, MΔ = -0.34 BW), and preferred landing leg knee internal rotation during the early loading phase. Despite these between group differences, the values for key variables that have been previously associated with ACL injury were higher in the netball group compared to previously published data for both female recreationally active and athletic populations. Both the netball and novice groups had very upright trunks (netball group, M = -2° to 4°; novice group, M = -3° - 0°) at initial ground contact and this may have reduced their ability to use the hip extensors to attenuate load during the loading phase of landing. When comparing trials with the greatest amount of trunk perturbation at landing to trials with the least, no significant differences were observed between variables related to ACL injury. Conclusion: Inclusion of task representative characteristics may produce more externally valid data and improve the assessment of landing biomechanics relating to injury compared to the commonly used drop landing. Specifically, an external focus elicited by including a ball may produce more game-like movement control; while jumping from the ground as opposed to stepping off a raised surface reduces the asymmetry of the landing task. The high-performance female netball players landed with smaller values in several biomechanical variables related to ACL injury risk compared to females who had never played a landing sport. However, the netball cohort still displayed relatively high values for several biomechanical variables associated with ACL injury risk, which may indicate they are underprepared for the physical demands of dynamic sport. The ability to perform dynamic tasks with low risk landing biomechanics is likely a key issue for many young females, and targeted training interventions are likely crucial for any individual participating in sport. Previous research has shown that this may cause unfavourable lower limb landing biomechanics, and therefore players may benefit from learning to increase posterior displacement of the pelvis combined with forward trunk inclination during landing. Finally, trunk perturbations initiated by reaching for a suspended netball did not result in any significant differences in variables related to ACL injury.

The Influence of Task Design when Assessing Landing Biomechanics Related to ACL Injury: A Study of Netball Players and Females Inexperienced at Landing

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