The role of trunk stability in landing mechanics
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Reference: EXOS
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Reference: EXOS Instagram
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Trunk flexion is coupled with hip and knee flexion (Yu et al, 2006; Blackburn and Padua, 2008), both modulators of ground reaction force and anterior shear. Further, trunk flexion has been associated with a decrease in ACL loading (Blackburn and Padua, 2009).
Worth noting is that this research has referenced trunk angle as the "trunk reference frame relative to the thigh reference frame" - with kinematic sensors placed between T12/L1 and C7/T1 to form a trunk reference frame, and kinematic sensors placed between the hip and knee to form a thigh reference frame. Trunk flexion thus indicates a gross "reference frame" relative to another - the thigh reference frame. While the thigh can not flex, the trunk can - two people can have the same trunk flexion angle but have different different segmental flexion or extension between the T12/L1 and C7/T1. The clinical implications of this are that a person who is segmentally flexing at the trunk (between T12/L1 and C7/T1) is expressing a pattern of flexion. This is associated with knee and hip flexion, modulating forces at the knee, which is good. But, segmental trunk flexion is also associated with hip adduction/internal rotation, which is not good for limiting valgus forces at the knee. Frank et al, (2013) have demonstrated that a combination of "greater trunk flexion displacement" and hip internal rotation explained nearly half of the variability in "internal knee external rotation moment". The latter term is an inverse dynamics term mean to be related to external knee internal rotation moments and represent the body's resistance to external moments.
To modulate potentially damaging forces at the knee, gross trunk flexion on landing is desirable, but with segmental "stiffness" to stabilise against hip adduction/internal rotation.
Further, in cutting movements, trunk rotation towards the new direction of travel (in combination with less hip adduction) is associated with less requirement to resist valgus forces at the knee (Frank et al, 2013).
Consider the lines of force required to stabilise against segmental trunk flexion/rotation - they include posterior elements predominantly, including spinal rotators and spinal extensors, all linked to hip external rotators and extensors via general motor patterns and myofascial lines.
Clinically, and in training, trunk flexion can be executed with segmental neutral/extension, thus modulating lower quarter forces and maintaining anti-hip adduction/internal rotation moments.
Such strategies include drop landings with external cues that include: "eyes forward on landing", or the addition of "throw your elbows back" on landing. See video link.
Yu, B., Lin, C. F., & Garrett, W. E. (2006). Lower extremity biomechanics during the landing of a stop-jump task. Clin Biomech (Bristol, Avon), 21(3), 297-305. doi:10.1016/j.clinbiomech.2005.11.003
Blackburn, J. T., & Padua, D. A. (2008). Influence of trunk flexion on hip and knee joint kinematics during a controlled drop landing. Clin Biomech (Bristol, Avon), 23(3), 313-319. doi:10.1016/j.clinbiomech.2007.10.003
Blackburn, J. T., & Padua, D. A. (2009). Sagittal-Plane Trunk Position, Landing Forces, and Quadriceps Electromyographic Activity. J Athl Train, 44(2), 174-179.
Frank, B., Bell, D. R., Norcross, M. F., Blackburn, J. T., Goerger, B. M., & Padua, D. A. (2013). Trunk and hip biomechanics influence anterior cruciate loading mechanisms in physically active participants. Am J Sports Med, 41(11), 2676-2683. doi:10.1177/0363546513496625
Worth noting is that this research has referenced trunk angle as the "trunk reference frame relative to the thigh reference frame" - with kinematic sensors placed between T12/L1 and C7/T1 to form a trunk reference frame, and kinematic sensors placed between the hip and knee to form a thigh reference frame. Trunk flexion thus indicates a gross "reference frame" relative to another - the thigh reference frame. While the thigh can not flex, the trunk can - two people can have the same trunk flexion angle but have different different segmental flexion or extension between the T12/L1 and C7/T1. The clinical implications of this are that a person who is segmentally flexing at the trunk (between T12/L1 and C7/T1) is expressing a pattern of flexion. This is associated with knee and hip flexion, modulating forces at the knee, which is good. But, segmental trunk flexion is also associated with hip adduction/internal rotation, which is not good for limiting valgus forces at the knee. Frank et al, (2013) have demonstrated that a combination of "greater trunk flexion displacement" and hip internal rotation explained nearly half of the variability in "internal knee external rotation moment". The latter term is an inverse dynamics term mean to be related to external knee internal rotation moments and represent the body's resistance to external moments.
To modulate potentially damaging forces at the knee, gross trunk flexion on landing is desirable, but with segmental "stiffness" to stabilise against hip adduction/internal rotation.
Further, in cutting movements, trunk rotation towards the new direction of travel (in combination with less hip adduction) is associated with less requirement to resist valgus forces at the knee (Frank et al, 2013).
Consider the lines of force required to stabilise against segmental trunk flexion/rotation - they include posterior elements predominantly, including spinal rotators and spinal extensors, all linked to hip external rotators and extensors via general motor patterns and myofascial lines.
Clinically, and in training, trunk flexion can be executed with segmental neutral/extension, thus modulating lower quarter forces and maintaining anti-hip adduction/internal rotation moments.
Such strategies include drop landings with external cues that include: "eyes forward on landing", or the addition of "throw your elbows back" on landing. See video link.
Yu, B., Lin, C. F., & Garrett, W. E. (2006). Lower extremity biomechanics during the landing of a stop-jump task. Clin Biomech (Bristol, Avon), 21(3), 297-305. doi:10.1016/j.clinbiomech.2005.11.003
Blackburn, J. T., & Padua, D. A. (2008). Influence of trunk flexion on hip and knee joint kinematics during a controlled drop landing. Clin Biomech (Bristol, Avon), 23(3), 313-319. doi:10.1016/j.clinbiomech.2007.10.003
Blackburn, J. T., & Padua, D. A. (2009). Sagittal-Plane Trunk Position, Landing Forces, and Quadriceps Electromyographic Activity. J Athl Train, 44(2), 174-179.
Frank, B., Bell, D. R., Norcross, M. F., Blackburn, J. T., Goerger, B. M., & Padua, D. A. (2013). Trunk and hip biomechanics influence anterior cruciate loading mechanisms in physically active participants. Am J Sports Med, 41(11), 2676-2683. doi:10.1177/0363546513496625