THE INFLUENCE OF FILTERING CUTOFF FREQUENCY ON [PDF]

THE INFLUENCE OF FILTERING CUTOFF FREQUENCY ON LANDING ... task for determining knee injury risk. Hewett ... Spearman ra

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THE INFLUENCE OF FILTERING CUTOFF FREQUENCY ON LANDING BIOMECHANICS MEASURED DURING A DROP VERTICAL JUMP 1

Ben D. Roewer, 3,4 Kevin R. Ford Ph.D., 1,2,3,4 Gregory D. Myer Ph.D., 1,2,3,4 Timothy E. Hewett, Ph.D.

1

Sports Health & Performance Institute, The Ohio State University, Columbus, OH 43221, USA Departments of Physiology and Cell Biology, Orthopaedic Surgery, Family Medicine and Biomedical Engineering, The Ohio State University, Columbus, OH 43221, USA 3 Division of Sports Medicine, Cincinnati Children’s Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229, USA 4 Department of Pediatrics and Orthopaedic Surgery, College of Medicine, University of Cincinnati, Cincinnati, OH 45221, USA Email: [email protected], web: http://sportsmedicine.osu.edu/ 2

The drop vertical jump (DVJ) is a useful movement task for determining knee injury risk. Hewett et al. used the DVJ to prospectively screen young female athletes for future anterior cruciate ligament injuries [1]. Peak knee abduction moment (KAM) measured during a DVJ predicted future ACL injury risk with 78% sensitivity and 73% specificity. Prior investigators have purported that it is necessary to filter marker and force data at the same frequency in order to calculate accurate joint moment data [2]. Joint moments derived from inverse dynamic techniques may be large when kinematic and force plate data are not filtered at the same frequency; however, the potential for erroneous calculation of joint torques is largely dependent on the maneuver, the joint of interest and the axis of rotation and [3]. The purpose of the present study was to determine the effects of kinematic and kinetic filtering cutoff frequencies on the peak KAM calculated during a DVJ. We hypothesized that the choice of filtering cutoff frequency would not significantly affect the peak KAM nor would it significantly alter the order of subjects ranked based on their peak KAM.

Trials were accepted if the subject’s feet made simultaneous and isolated contact with two force places embedded into the laboratory floor (Bertec corp. Worthington, OH). Three-dimensional marker position data were sampled at 240Hz using eight infrared cameras (Vicon, Oxford Metric Ltd. London, UK). Ground reaction force data were sampled at 1200Hz. Marker and force data were low-pass filtered at the same frequency (10Hz, 12Hz, and 15Hz) and also at mismatched frequencies (10-50Hz, 12-50Hz, 15-50Hz respectively) using a bi-directional Butterworth filter. Data were processed using custom Visual 3D (C-motion Inc. Germantown, MD) and Matlab (Mathworks Inc. Natick, MA) coding. Peak external KAM during 100% of stance was compared across all filtering conditions using an ANOVA with two repeated measures (limb x filtering cutoff frequency). Spearman rank correlation was used to test the effect of filtering condition on the rank order of athletes based on their peak KAMs. Significance for all tests was set at α < 0.05. Statistical significance for the post hoc paired t-tests was adjusted using a Bonferonni correction (α < 0.003).

METHODS

RESULTS AND DISCUSSION

Twenty-two female high school volleyball players were tested prior to the onset of their sport seasons. Subject height, body mass and the average of three maximum vertical jump attempts were recorded. Forty-three 9 mm retroreflective markers were placed on anatomical landmarks. Each subject performed three DVJ trials from a 31cm tall box.

No effect of limb was detected (p = 0.206) so data for both limbs were collapsed and analyzed. A main effect of filtering condition was detected for peak KAM (p < 0.001). Significant differences in peak KAM were detected among all of the matched filtering conditions (p < 0.003), but no differences were detected among all of the mismatched filtering

INTRODUCTION

conditions (p ≥ 0.003). The average mismatchfiltered peak KAM values were greater than the match-filtered peak KAM values (p < 0.001) (Fig. 1).

The effect of mismatched filtering was not consistent across all subjects. Large KAMs were not observed at initial contact when matched filtering was applied. However, when mismatched filtering was applied, some subjects showed large KAMS at initial contact (Fig. 2B) while others did not (Fig. 2A). The rank order of mismatch-filtered peak KAM values significantly covaried with the order of match-filtered peak KAM values (p < 0.001). In other words, athletes who had the largest peak KAMs when matched filtering was applied also had the largest peak KAMs when mismatched filtering was applied. CONCLUSIONS

Figure 1: The average external knee abduction moment during the drop vertical jump for each filtering condition. Time-normalized data for the first 50% of stance are presented to clarify the effect of filtering condition on KAM near initial contact.

While filtering cutoff frequency affected the magnitude of the peak KAM calculated during a DVJ it did not affect the rank order of individual athletes. An important question remains unanswered: “Are the high knee moments reported by prior investigators [1] artifacts as postulated [2] or are they authentically large knee moments that may hold high predictive value for assessing future knee injury risk?” REFERENCES 1. Hewett,

et al. American Journal of Sports Medicine, 33, 492-501, 2005. 2. Kristianslund, et al. Journal of Biomechanics, 45 666-671, 2012. 3. Hewett, et al. Journal of Biomechanics, In Press 2012. ACKNOWLEDGEMENTS Figure 2: The average external knee abduction moment for two representative subjects produced under matched and mismatched filtering conditions.

Funding was provided by the National Institutes of Health grants (RO1-AR049735, R01-AR055563, R01-AR056259).

Table 1: Peak knee abduction moment calculated for each filtering condition during 100% of stance for the drop vertical jump. (n=22). Means standard deviations are presented. Cutoff frequency (10-10) Hz (12-12) Hz (15-15) Hz (10-50) Hz (12-50) Hz (15-50) Hz (marker – force) Peak KAM (Nm) -24.0 ± 11.7 -24.5 ± 11.3 -25.5 ± 11.0 -31.1 ± 10.7 -31.0 ± 10.2 -31.0 ± 10.1

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