Award Date
8-1-2017
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Kinesiology and Nutrition Sciences
First Committee Member
Janet S. Dufek
Second Committee Member
John A. Mercer
Third Committee Member
Julia Freedman Silvernail
Fourth Committee Member
Brendan T. Morris
Number of Pages
122
Abstract
Landing strategies are evaluated to determine a performer’s favored neuromusculo-skeletal solution for the performance of the task. Depending on the strategy employed, a performer might increase his or her musculoskeletal injury potential, as defined by increased impact forces and/or demands on the involved joints. In recent history, the manner in which a performer modifies his or her strategy has been evaluated following the application of an added external mass during the impact phase of landings performed from atop an elevated platforms or a hanging position from a raised bar. Furthermore, the strategies evaluated in contemporary research are quantified using biomechanical factors during the impact phase of landing. These “strategies” describe the biomechanical responses to impact rather than the strategic positioning of the body segments in anticipation for impact. Nonetheless, the results of the available evaluations are inconsistent with respect to whether or not injury potential increases when an added external load is applied to a performer during landing. The inconsistent conclusions relative to effect of added external mass on injury potential during landing appears due in part to the tasks evaluated. Specifically, step-off landings (STL) from an elevated platform were found to be biomechanically different than vertical jump landings (VJL) during the impact phase. Unfortunately, the scarcity of empirical evidence comparing these tasks threatens the validity of that conclusion. Therefore, the purposes of this multiple-article dissertation were to (1) examine impact force and joint kinematic differences bilaterally during the impact phase of VJL and STL from equal heights to strengthen the current body of literature, (2) determine whether task-specific anticipatory strategies coincide with task-specific biomechanics during the impact phase of VJL and STL from equal heights, and (3) examine alterations and/or adjustments in the anticipatory strategies and associated impact phase mechanics that occur in response to both added external mass and changes in the arrangement of added external mass during VJL. For the first and second purposes, ten healthy adults performed fifteen VJL and fifteen STL from equal heights while three-dimensional kinematic and kinetic were obtained. For the third purpose, twenty-four healthy adults performed 32 VJL during various conditions of added external mass while three dimensional kinematic and kinetic were obtained. Specifically, eight trials were performed in each of the following added mass conditions: unloaded (UL; 0% added mass), split loaded (SL; 10% added mass arranged symmetrically over the trunk), front loaded (FL; 10% added mass arranged over the anterior portion of the trunk), and back loaded (BL; 10% added mass arranged over the posterior portion of the trunk). Relative to purpose one, it was found that different joint motions and impact attenuation parameters characterized VJL and STL during the impact phase of landing. Notable differences included greater hip, knee, and ankle flexion/dorsiflexion throughout the majority of impact during STL regardless of limb. Additionally, lesser hip, knee, and ankle joint displacement occurred during STL regardless of limb between the first (F1) and second (F2) peak vertical ground reaction force magnitudes, while greater joint displacement occurred between F2 and the end of the impact phase. Finally, knee joint angles at ground contact differed between limbs during STL only. In light of these differences, STL appeared to increase injury potential compared to VJL, though it was acknowledged that STL could also be used as a training tool to improve an athlete’s impact attenuation abilities during vertical landings characterized by asymmetrical lower body positions at ground contact. Relative to the second purpose, it was found that greater hip flexion angles occurred during STL 100ms pre-impact, 50ms pre-impact, and at ground contact and greater trail leg knee flexion angles occurred during STL at each pre-impact event compared to the lead leg. Additionally, greater trail leg knee flexion angles occurred during STL at each pre-impact event, while greater plantarflexion angles occurred during VJL at each pre-impact event. Finally, greater plantarflexion angles were detected at each event in the trail leg versus the lead leg during STL, and lesser hip and lead leg knee displacements occurred during STL in addition to greater trail leg knee displacement. Collectively, these results indicated a flexed-constrained anticipatory movement strategy was employed at the hip and knee joints during STL and the flexedconstrained strategy suggested different and less familiar task demands distinguish STL from VJL. As such, a link was identified between the different anticipatory movement strategies and the different impact attenuation parameters between VJL and STL. Relative to the third purpose, it was found that performing VJL when SL produced lesser peak vertical ground reaction force magnitude (referred to as F2 in the previous studies) and lesser relative impulse and lower extremity energy absorption magnitudes during early impact versus UL. These outcomes were due to both more constrained anticipatory knee joint motions and decreased biomechanical demands (potential energy) during SL versus UL. Thus, UL appeared to increased lower extremity injury potential relative to impact force and kinetic energy absorption magnitudes in comparison to SL. When determining the influence of slight changes in the arrangement of the external load, it was found that the BL arrangement increased the magnitude of kinetic energy absorbed by lower extremity during early impact in comparison to both SL and FL. Thus, both UL and BL were characterized by increased magnitudes of lower extremity energy absorption compared to SL and SL and FL, respectively. However, the unchanged percent contributions of the hip, knee, and ankle joints to the total energy absorbed suggested that no joint in particular was exposed to greater injury risk during UL and/or BL despite the increase in total energy absorbed lower extremity. In summary, full consideration of the biomechanical differences between landings from a jump (VJL) and landings from an elevated platform (STL) can help create training programs capable of producing desired performance outcomes without increasing injury potential. Further, individuals aiming to improve jumping and/or landing performance through the inclusion of added external mass via weighted vests (approximately 10% body mass) during VJL training should consider the use of a split loaded (SL) or front loaded (FL) weight vest arrangement. These arrangements should be considered for their capacity to achieve performance goals without being exposed to greater risk of injury as opposed to using zero added mass (UL) or a back loaded (BL) weight vest arrangement.
Disciplines
Biomechanics | Kinesiology
File Format
Degree Grantor
University of Nevada, Las Vegas
Language
English
Repository Citation
Harry, John Robert, "Biomechanical Adjustments during Landing in Response to Task Perturbations" (2017). UNLV Theses, Dissertations, Professional Papers, and Capstones. 3080.
http://dx.doi.org/10.34917/11156729
Rights
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