Browsing by Author "Streepey, Jefferson"

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    The Effect of Anterior Cruciate Ligament Reconstruction on Leg-Spring Stiffness During Hopping
    (2020-12) Wolfe, David K.; Bahamonde, Rafael; Streepey, Jefferson; Riley, Zachary; Naugle, Kelly; Beekley, Matthew
    Leg-Spring Stiffness (LSS) is the measure of the musculoskeletal, neuromuscular, and biomechanical functions of the human body, and an appropriate evaluation metric for changes brought on by Anterior Cruciate Ligament Reconstruction (ACLr). ACLr can lead to flexion and extension loss, resulting in increased stiffness of the musculotendinous units of the ACLr leg and thus changes in LSS. LSS can be measured using Kleg, but little is known about the validity and reliability of the different methods of LSS and Kleg calculations. The purpose of this study was to determine if ACLr leads to a change in LSS (as measured by Kleg) during hopping, and to compare results of the Spring-Mass calculation and knee Joint Torsional stiffness methods in the computation of the overall Kleg. Video data synchronize with GRF were used to compute the kinematic and kinetic variables. Mann-Whitney U tests were used to determine significant differences between the control and experimental group for the Spring-Mass method of calculation (p = 0.004), Joint Torsional method (p =0.44), Kknee (p = 0.29), and Kankle (p = 0.17). Cohen’s effect calculations showed small to medium effects for the KKnee, (d = 0.383) but moderate effect size for the KAnkle, (d = 0.541). Wilcoxon Signed Rank comparison for all the legs and (N=42) between computational methods were significant differences between computational methods (Z = 5.65, p = 0.000), and with a large effect size (Cohen’s d = 3.14). Similar results were found when comparing only the ACLr leg values (p = 0.005, Cohen’s d = 4.88). The comparison between ACL Leg vs Non-ACL leg for experimental group subjects was not significant in either calculation method (Spring-Mass p = 0.20, Z = -1.27; torque calculation p = 0.96, Z = -0.05). The spring-mass method was more stable and able to detect differences between the control and ACLr group. The lack of statistical differences in the joint torsion calculation method, as well as in comparing the unaffected leg to the ACLr leg in the experimental group, suggests that LSS may not be a precise enough measurement to determine the effects of an ACLr.
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    ENERGY RETURN OF DIFFERENT DESIGNS OF TRACK SPIKES
    (Office of the Vice Chancellor for Research, 2014-04-11) Bahamonde, Rafael E.; Streepey, Jefferson; Goyke, Lance; Myers, Adrian; Mikesky, Alan E.
    INTRODUCTION: Advances in technology and design have generated changes to the traditional track spike. Today, there are a number of different spike shapes, the four most common being needle, pyramid, post, and Christmas tree and modified Christmas tree (the last two are also referred to as “compression tier”) (see Figure 1). Running magazines, product advertisements, coaches, and manufacturers make claims about the potential effects of each type of spike design and their use in different situations. To our knowledge, these types of claims and other information regarding spikes or track surfaces, have not been tested and reported in the peer-reviewed literature. METHODS: The purpose of this preliminary study was to examine whether different shaped spikes elicit quantifiable differences in energy return on a Mondo track surface, the most commonly used at track venues. Five different shaped spikes all 7mm in length were used in this study (see Figure #1). The spikes chosen are those commonly used by athletes on various indoor and outdoor track surfaces. The load-deformation between the spikes the track was measured using a Bose Electroforce 3200 (Eden Praire, MN) testing device. OneWay ANOVAs using Sigma Plot 10.5 (Systat Inc., Richmond, CA) were performed to test for significant differences between spikes. Tukey post-hoc comparisons were performed at the p=0.05 level. RESULTS: Figure 2 shows the ANOVA results [F (4,49)=54.78, p<.001] and Tukey post-hoc comparison for the energy returned. The MTREE spike generated the greatest amount of energy returned and was significantly different from the other spikes (p<=0.05). The PYRA spike generated second largest amount of energy returned and was significant different from the PIN and POST spikes. The PIN or needle spike, as expected, had the least amount of energy returned. All spikes penetrated the track surface. DISCUSSION: The notion that compression spikes have less track penetration is unfounded. All the spikes tested penetrated the track under loads less than 105 N. Considering that vertical ground reaction force (GRF) increases linearly during walking and running from 1.2 BW to approximately 2.5 BW at 6.0 m s−1 and remains constant during forward lean sprinting at higher speeds, the likehood of any of the tested spikes not penetrating the Mondo track surface seems improbable (Keller et al., 1996). For the Mondo track the spike with the largest energy return was the MTREE design. This MTREE provided the largest spike surface area, which helped it to compress the track. The common PIN design provided the least energy return but absorbed the least amount of energy. All the compression spikes seem to provide larger amounts of energy return when compared to the PIN. The measured energy returned by the various spikes is relatively small (N*mm). However, for this study, the energy return was determined for only one spike while most sprint shoes have a sole plate with up to 10 mounted spikes. While it is difficult to assess how much of the energy returned in the spike-track surface interaction might actually aid the sprinter, these findings are nevertheless noteworthy. It is not uncommon for results in sprint races to be separated by only thousandths of a second, where even small levels of energy return could potentially make the difference between winning or losing a race. CONCLUSION: This study shows that spike design affects the amount of energy returned and absorbed by a Mondo track surface. While all of the spikes tested penetrated the track surface, the modified Christmas tree design returned the most energy on the Mondo surface. Knowledge of which spike design offers the highest energy return on the various track surfaces that athletes compete on could be useful to coaches and athletes, as well as, spike and track manufacturers and thus is worthy of further investigation.