John M Popovich

Michigan State University, Ист-Лансинг, Michigan, United States

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Publications (28)46.7 Total impact

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    ABSTRACT: Determining the reliability of measurements used to quantify head-neck motor control is necessary before they can be used to study the effects of injury or treatment interventions. Thus, the purpose of this study was to determine the within- and between-day reliability of position tracking, position stabilization and force tracking tasks to quantify head-neck motor control. Ten asymptomatic subjects performed these tasks on two separate days. Position and force tracking tasks required subjects to track a pseudorandom square wave input signal by controlling their head-neck angular position (position tracking) or the magnitude of isometric force generated against a force sensor by the neck musculature (force tracking) in the sagittal plane. Position stabilization required subjects to maintain an upright head position while pseudorandom perturbations were applied to the upper body using a robotic platform. Within-day and between-day reliability of the frequency response curves were assessed using coefficients of multiple correlations (CMC). Root mean square error (RMSE) and mean bandpass signal energy, were computed for each task and between-day reliability was calculated using intra-class correlation coefficients (ICC). Within- and between-day CMCs for the position and force tracking tasks were all ≥0.96, while CMCs for position stabilization ranged from 0.72 to 0.82. ICCs for the position and force tracking tasks were all ≥0.93. For position stabilization, ICCs for RMSE and mean bandpass signal energy were 0.66 and 0.72, respectively. Measures of sagittal plane head-neck motor control using position tracking, position stabilization and force tracking tasks were demonstrated to be reliable. Copyright © 2014 Elsevier Ltd. All rights reserved.
    Journal of Biomechanics 11/2014; 48(3). DOI:10.1016/j.jbiomech.2014.11.023 · 2.50 Impact Factor
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    ABSTRACT: Objectives: To compare the strength of augmented versus non-augmented fixation techniques for stabilizing vertical shear femoral neck fractures. Methods: Two surgical screw constructs were tested with and without augmentation using 40 composite femurs: (1) 7.3 mm cannulated screws placed in an inverted triangular configuration, and (2) 135 degree dynamic hip screw (DHS). The augmentation consisted of a 2.7 mm locking plate placed on the anterior-inferior femoral neck. Specimens in all four groups were tested with load to failure, while failure loads, energy absorbed to failure, and axial stiffness were determined. These data were then analyzed using a two-way (construct x augmentation) ANOVA. Results: There was no statistically significant interaction between screw construct and augmentation for load to failure (P = 0.11). Augmentation with the 2.7 mm locking plate increased failure loads in both constructs on average by 83% (2,409 N vs.4,417 N, P < 0.01). Femurs instrumented with cannulated screws had 26% higher loads to failure than those instrumented with DHS (3,879 N vs. 3,087 N, P < 0.01). On average, the augmentation increased energy absorbed to failure by 183% and constructs' stiffness by 35%. Conclusions: The strength of surgical repairs of the vertical shear femoral neck fractures can be significantly augmented with the 2.7 mm locking plate. The construct with the cannulated screws was significantly stronger than the DHS construct. Copyright (C) 2015 Wolters Kluwer Health, Inc. All rights reserved.
    Journal of Orthopaedic Trauma 07/2014; 29(3). DOI:10.1097/BOT.0000000000000205 · 1.54 Impact Factor
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    ABSTRACT: We are developing a series of systems science-based clinical tools that will assist in modeling, diagnosing, and quantifying postural control deficits in human subjects. In line with this goal, we have designed and constructed an experimental device and associated experimental task for identification of the human postural control system. In this work, we present a Quadratic Programming (QP) technique for optimizing a time-domain experimental input signal for this device. The goal of this optimization is to maximize the information present in the experiment, and therefore its ability to produce accurate estimates of several desired postural control parameters. To achieve this, we formulate the problem as a non-convex QP and attempt to maximize a measure (T-optimality condition) of the experiment's Fisher Information Matrix (FIM) under several constraints. These constraints include limits on the input amplitude, physiological output magnitude, subject control amplitude, and input signal autocorrelation. Because the autocorrelation constraint takes the form of a Quadratic Constraint (QC), we replace it with a conservative linear relaxation about a nominal point, which is iteratively updated during the course of optimization. We show that this iterative descent algorithm generates a convergent suboptimal solution that guarantees monotonic non-increasing of the cost function while satisfying all constraints during iterations. Finally, we present example experimental results using an optimized input sequence.
    2014 American Control Conference - ACC 2014; 06/2014
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    Jo Armour Smith, John M Popovich, Kornelia Kulig
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    ABSTRACT: Study Design Cross-sectional, laboratory study. Objectives To compare peak lower limb, pelvis, and trunk kinematics and inter-joint and inter-segmental coordination in women with strong and weak hip muscle performance. Background Persons with lower extremity musculoskeletal disorders often demonstrate a combination of weak hip musculature and altered kinematics during weight bearing dynamic tasks. However, the association between hip strength and kinematics independent of pathology or pain is unclear. Methods Peak hip extensor and abductor torque were measured in 150 healthy young women. Of these, 10 fit the criteria for the strong group and 9 for the weak group. Kinematics of the hip, knee, pelvis, and trunk were measured during the stance phases of walking and rate-controlled hopping. Hip/knee and pelvis/trunk coordination were calculated using the vector coding technique. Results There were no group differences in peak hip, knee, or pelvis kinematics. Weak participants demonstrated greater trunk lateral bend towards the stance limb during hopping (P = .002, effect size d = 1.88). In the transverse plane, the weak group utilized less in-phase coordination between the hip and the knee during walking (P = .036, d = 1.45) and more anti-phase coordination between the hip and knee during hopping (P = .03, d = 1.47). Conclusion In the absence of pain or pathology, poor hip muscle performance does not affect peak hip or knee joint kinematics in young women, but is associated with significantly different lower limb and trunk/pelvis coordination during weight bearing dynamic tasks. J Orthop Sports Phys Ther, Epub 10 May 2014. doi:10.2519/jospt.2014.5028.
    05/2014; 44(7). DOI:10.2519/jospt.2014.5028
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    ABSTRACT: Objective:The purpose of the study was to examine changes in quality of life measures in patients who have undergone an intensive exercise program following a single level microdiskectomy.Design:Randomized controlled trial with blinded examiners.Setting:The study was conducted in outpatient physical therapy clinics.Subjects:Ninety-eight participants (53 male, 45 female) who had undergone a single-level lumbar microdiskectomy allocated to receive exercise and education or education only.Interventions:A 12-week periodized exercise program of lumbar extensor strength and endurance training, and mat and upright therapeutic exercises was administered.Outcome measures:Quality of life was tested with the Short Form 36 (SF-36). Measurements were taken 4-6 weeks postsurgery and following completion of the 12-week intervention program. Since some participants selected physical therapy apart from the study, analyses were performed for both an as-randomized (two-group) design and an as-treated (three-group) design.Results:In the two-group analyses, exercise and education resulted in a greater increase in SF-36 scales, role physical (17.8 vs. 12.1) and bodily pain (13.4 vs. 8.4), and the physical component summary (13.2 vs. 8.9). In the three-group analyses, post-hoc comparisons showed exercise and education resulted in a greater increase in the SF-36 scales, physical function (10.4 vs. 5.6) and bodily pain (13.7 vs. 8.2), and the physical component summary (13.7 vs. 8.9) when compared with usual physical therapy.Conclusions:An intensive, progressive exercise program combined with education increases quality of life in patients who have recently undergone lumbar microdiskectomy.
    Clinical Rehabilitation 02/2014; 28(9). DOI:10.1177/0269215514525059 · 2.18 Impact Factor
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    ABSTRACT: In this brief, we present a set of techniques for finding a cost function to the time-invariant linear quadratic regulator (LQR) problem in both continuous- and discrete-time cases. Our methodology is based on the solution to the inverse LQR problem, which can be stated as: does a given controller K describe the solution to a time-invariant LQR problem, and if so, what weights Q and R produce K as the optimal solution? Our motivation for investigating this problem is the analysis of motion goals in biological systems. We first describe an efficient linear matrix inequality (LMI) method for determining a solution to the general case of this inverse LQR problem when both the weighting matrices Q and R are unknown. Our first LMI-based formulation provides a unique solution when it is feasible. In addition, we propose a gradient-based, least-squares minimization method that can be applied to approximate a solution in cases when the LMIs are infeasible. This new method is very useful in practice since the estimated gain matrix K from the noisy experimental data could be perturbed by the estimation error, which may result in the infeasibility of the LMIs. We also provide an LMI minimization problem to find a good initial point for the minimization using the proposed gradient descent algorithm. We then provide a set of examples to illustrate how to apply our approaches to several different types of problems. An important result is the application of the technique to human subject posture control when seated on a moving robot. Results show that we can recover a cost function which may provide a useful insight on the human motor control goal.
    IEEE Transactions on Control Systems Technology 01/2014; 23(2):1-1. DOI:10.1109/TCST.2014.2343935 · 2.52 Impact Factor
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    ABSTRACT: System-based methods have been applied to assess trunk motor control in people with and without back pain, although the reliability of these methods has yet to be established. Therefore, the goal of this study was to quantify within- and between-day reliability using systems-based methods involving position and force tracking and stabilization tasks. Ten healthy subjects performed six tasks, involving tracking and stabilizing of trunk angular position in the sagittal plane, and trunk flexion and extension force. Tracking tasks involved following a one-dimensional, time-varying input signal displayed on a screen by changing trunk position (position tracking) or trunk force (force tracking). Stabilization tasks involved maintaining a constant trunk position (position stabilization) or constant trunk force (force stabilization) while a sagittal plane disturbance input was applied to the pelvis using a robotic platform. Time and frequency domain assessments of error (root mean square and H2 norm, respectively) were computed for each task on two separate days. Intra-class correlation coefficients (ICC) for error and coefficients of multiple correlations (CMC) for frequency response curves were used to quantify reliability of each task. Reliability for all tasks was excellent (between-day ICC≥0.8 and CMC>0.75, within-day CMC>0.85). Therefore, position and force control tasks used to assess trunk motor control can be deemed reliable.
    Journal of Biomechanics 10/2013; 47(1). DOI:10.1016/j.jbiomech.2013.10.018 · 2.50 Impact Factor
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    ABSTRACT: BACKGROUND CONTEXT: Intervertebral disc and facet joints are the two primary load-bearing structures of the lumbar spine, and altered loading to these structures may be associated with frontal plane spinal deviations. PURPOSE: To determine the load on the lumbar facet joint and intervertebral disc under simulated frontal plane pelvic obliquity combined loading, an in vitro biomechanical study was conducted. STUDY DESIGN/SETTING: An in vitro biomechanical study using a repeated-measures design was used to compare L4-L5 facet joint and intervertebral disc loading across pure moment and combined loading conditions. METHODS: Eight fresh-frozen lumbosacral specimens were tested under five loading conditions: flexion/extension, lateral bending, axial rotation using pure moment bending (±10 Nm), and two additional tests investigating frontal plane pelvic obliquity and axial rotation (sacrum tilted left 5° and at 10° followed by a ±10-Nm rotation moment). Three-dimensional kinematics, facet load, and intradiscal pressures were recorded from the L4-L5 functional spinal unit. RESULTS: Sagittal and frontal plane loading resulted in significantly smaller facet joint forces compared with conditions implementing a rotation moment (p<.05). The facet joint had the highest peak load during the 10° combined loading condition (124.0±30.2 N) and the lowest peak load in flexion (26.8±16.1 N). Intradiscal pressure was high in lateral flexion (495.6±280.9 kPa) and flexion (429.0±212.9 kPa), whereas intradiscal pressures measured in rotation (253.2±135.0 kPa) and 5° and 10° combined loading conditions were low (255.5±132.7 and 267.1±127.1 kPa, respectively). CONCLUSIONS: Facet loading increased during simulated pelvic obliquity in frontal and transverse planes, whereas intradiscal pressures were decreased compared with sagittal and frontal plane motions alone. Altered spinopelvic alignment may increase the loads experienced by spinal tissue, especially the facet joints.
    The spine journal: official journal of the North American Spine Society 05/2013; 13(11). DOI:10.1016/j.spinee.2013.04.011 · 2.80 Impact Factor
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    ABSTRACT: Why can we balance a yardstick but not a pencil on the tip of our finger? As with other physical systems, human motor control has constraints, referred to as bandwidth, which restricts the range of frequency over which the system can operate within some tolerated level of error. To investigate control bandwidth, the natural frequency of a stick used during a stick balancing was modified by adjusting the height of a mass attached to the stick. The ability to successfully balance the stick with the mass positioned at four different heights was determined. In addition, electromyographic signals from forearm and trunk muscles were recorded during the trials. We hypothesized that (1) the probability of success would decrease as mass height decreased, and (2) the level of muscle activation in both agonist and antagonist would be linearly related to the natural frequency of the stick. Results showed that as the mass height decreased the probability of successfully balancing the stick decreased. Changes in the probability of success with respect to mass height showed a threshold effect, suggesting that limits in human control bandwidth were approached at the lowest mass height. Also, the level of muscle activation in both the agonist and antagonist of the forearm and trunk were linearly related to the natural frequency of the stick. These changes in muscle activation suggest that the CNS adapts muscle activation to task dynamics, possibly to improve control bandwidth.
    Journal of Neurophysiology 02/2013; 109(10). DOI:10.1152/jn.00429.2012 · 3.04 Impact Factor
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    ABSTRACT: In an effort to better understand the human head-neck target tracking response, we have developed a procedure for designing a robustly optimal experimental configuration for system identification. This configuration is comprised of a parametrized input sequence along with physical parameters for the experiment. We have developed both nominal and experimental models containing uncertainties for the target tracking task based on several preliminary experimental data sets, and identified a feasible population of subject controller parameters. We applied a min-max optimization scheme to minimize a performance cost over the feasible experimental configurations, while simultaneously maximizing it over the population of subject controller parameters. In this way, a minimum level of design performance for any subject within the defined population can be guaranteed. We show that in the worst-case, the performance cost is 0.473 in flexion/extension, and 0.122 in axial rotation.
    ASME 2012 5th Annual Dynamic Systems and Control Conference joint with the JSME 2012 11th Motion and Vibration Conference; 10/2012
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    ABSTRACT: In this study, we investigated trunk coordination during rate-controlled bipedal vertical dance jumps. The aims of the study were to investigate the pattern of coordination and the magnitude of coordination variability within jump phases and relative to phase-defining events during the jump. Lumbar and thoracic kinematics were collected from seven dancers during a series of jumps at 95 beats per minute. The vector coding technique was used to quantify the pattern and variability of trunk coordination. Coordination was predominantly anti-phase during propulsion and landing. Mean coordination variability peaked just before the landing phase and at the transition from landing to propulsion phases, and was lowest during the propulsion phase just before toe-off. The results indicate that peaks in variability could be explained by task and phase-specific biomechanical demands.
    Journal of Sports Sciences 11/2011; 30(2):139-47. DOI:10.1080/02640414.2011.624541 · 2.10 Impact Factor
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    ABSTRACT: Controlled laboratory study using a cross-sectional design. To characterize ankle and hip muscle performance in women with posterior tibial tendon dysfunction (PTTD) and compare them to matched controls. We hypothesized that ankle plantar flexor strength, and hip extensor and abductor strength and endurance, would be diminished in women with PTTD and this impairment would be on the side of dysfunction. Individuals with PTTD demonstrate impaired walking abilities. Walking gait is strongly dependent on the performance of calf and hip musculature. Thirty-four middle-aged women (17 with PTTD) participated. Ankle plantar flexor strength was assessed with the single-leg heel raise test. Hip muscle performance, including strength and endurance, were dynamometrically measured. Differences between groups and sides were assessed with a mixed-model analysis of variance. Females with PTTD performed significantly fewer single-leg heel raises and repeated sagittal and frontal plane non-weight-bearing leg lifts, and also had lower hip extensor and abductor torques than age-matched controls. There were no differences between sides for hip strength and endurance measures for either group, but differences between sides in ankle strength measures were noted in both groups. Women with PTTD demonstrated decreased ankle and hip muscle performance bilaterally.
    09/2011; 41(9):687-94. DOI:10.2519/jospt.2011.3427
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    ABSTRACT: Low back pain affects a substantial number of adults each year and is persistent or recurrent for many. Self-efficacy is an important predictor of functional recovery. The purpose of this investigation was to assess the preliminary reliability and validity of the Low Back Activity Confidence Scale (LoBACS) for individuals with histories of low back pain or lumbar surgery. Two overlapping samples of patients who had undergone a microdiskectomy participated: a test-retest sample of 21 individuals and a validity sample of 53 individuals. Low Back Activity Confidence Scale items pertaining to self-efficacy for functional activities (FnSE subscale), self-regulation of back health (Self-RegSE subscale), and regular exercise (ExSE subscale) were generated from existing literature and clinical observations. The test-retest sample completed the LoBACS twice, approximately 10 days apart. The validity sample completed the LoBACS and measures of functional performance, self-reported leisure and occupational physical activity, pain, fear beliefs, disability, and quality of life. The FnSE, Self-RegSE, and ExSE subscale scores and LoBACS total score had excellent to acceptable test-retest reliability (intraclass correlation coefficients of .924, .634, .710, and .850, respectively) and internal consistency (Cronbach α coefficients of .924, .804, .941, and .911, respectively). The LoBACS subscales were correlated in expected directions with physical performance, physical activity, pain, fear beliefs, disability, and quality of life, providing initial evidence of concurrent validity. The findings provide preliminary content and concurrent validity and interrater and internal consistency reliability for the LoBACS measure of self-efficacy for individuals with histories of low back pain and lumbar microdiskectomy.
    Physical Therapy 08/2011; 91(11):1592-603. DOI:10.2522/ptj.20100135 · 3.25 Impact Factor
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    ABSTRACT: Controlled laboratory study using a cross-sectional design. To analyze lower extremity kinematics during takeoff of a "saut de chat" (leap) in dancers with and without a history of Achilles tendinopathy (AT). We hypothesized that dancers with AT would demonstrate different kinematic strategies compared to dancers without pathology, and that these differences would be prominent in the transverse and frontal planes. AT is a common injury experienced by dancers. Dance leaps such as the saut de chat place a large demand on the Achilles tendon. Sixteen female dancers with and without a history of AT (mean ± SD age, 18.8 ± 1.2 years) participated. Three-dimensional kinematics at the hip, knee, and ankle were quantified for the takeoff of the saut de chat, using a motion analysis system. A force platform was used to determine braking and push-off phases of takeoff. Peak sagittal, frontal, and transverse plane joint positions during the braking and push-off phases of the takeoff were examined statistically. Independent samples t tests were used to evaluate group differences (α = .05). The dancers in the tendinopathy group demonstrated significantly higher peak hip adduction during the braking phase of takeoff (mean ± SD, 13.5° ± 6.1° versus 7.7° ± 4.2°; P = .046). During the push-off phase, dancers with AT demonstrated significantly more internal rotation at the knee (13.2° ± 5.2° versus 6.9° ± 4.9°; P = .024). Dancers with AT demonstrate increased peak transverse and frontal plane kinematics when performing the takeoff of a saut de chat. These larger displacements may be either causative or compensatory factors in the development of AT.
    08/2011; 41(8):606-13. DOI:10.2519/jospt.2011.3580
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    John M Popovich, Kornelia Kulig
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    ABSTRACT: Hip muscle weakness has been associated with altered lower extremity mechanics and the increased likelihood of receiving treatment for low back problems, although biomechanical injury mechanisms focused on the trunk have not been investigated. The purpose of this study was to compare lumbopelvic kinematic variables and muscle activation of the trunk and gluteal muscles in females with strong and weak hip muscle strength during a demanding single-leg task. Twenty-two asymptomatic females were categorized into a strong or weak group (11 per group) as determined by isometric hip extension and abduction dynamometry profiles. Participants performed a single-leg landing task during which three-dimensional lumbopelvic kinematics and trunk (lumbar erector spinae, external obliques, and rectus abdominis) and gluteal (gluteus maximus and gluteus medius) muscle activities were recorded. Peak lumbopelvic angular displacement, total angular excursion, and mean and peak angular velocity during the first 0.5 s of landing were reported. Mean normalized EMG and muscle cocontraction index (between the lumbar erector spinae and the external obliques) were also reported. Significant between-group differences existed for each of the following: peak displacement, excursion, velocity, and muscle activity. Differences in peak angular displacement occurred in the frontal plane, whereas excursion differences were observed in all planes. Differences in peak velocity were noted in the sagittal and frontal planes. Weaker subjects showed increased muscle activation (across all muscles except the rectus abdominis) and cocontraction index. Individuals with diminished hip muscle strength exhibit greater lumbopelvic angular displacement, velocity, and muscle activity during the single-leg landing task. Future studies targeting hip strengthening may provide more insight to rehabilitation protocols as well as the relation between hip strength, low back motion, and muscle activity.
    Medicine and science in sports and exercise 06/2011; 44(1):146-53. DOI:10.1249/MSS.0b013e3182267435 · 4.46 Impact Factor
  • J B Welcher, J M Popovich, T P Hedman
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    ABSTRACT: A new sensor array intended to accurately and directly measure spatial and time-dependent pressures within a highly curved biological intra-articular joint was developed and tested. To evaluate performance of the new sensor array for application within intra-articular joints generally, and specifically to fit within the relatively restrictive space of the lumbar spine facet joint, geometric constraints of length, width, thickness and sensor spatial resolution were evaluated. Additionally, the effects of sensor array curvature, frequency response, linearity, drift, hysteresis, repeatability, and total system cost were assessed. The new sensor array was approximately 0.6mm in thickness, scalable to below the nominal 12 mm wide by 15 high lumbar spine facet joint size, offered no inherent limitations on the number or spacing of the sensors with less than 1.7% cross talk with sensor immediately adjacent to one another. No difference was observed in sensor performance down to a radius of curvature of 7 mm and a 0.66±0.97% change in sensor sensitivity was observed at a radius of 5.5mm. The sensor array had less than 0.07 dB signal loss up to 5.5 Hz, linearity was 0.58±0.13% full scale (FS), drift was less than 0.2% FS at 250 s and less than 0.6% FS at 700 s, hysteresis was 0.78±0.18%. Repeatability was excellent with a coefficient of variation less than 2% at pressures between 0 and 1.000 MPa. Total system cost was relatively small as standard commercially available data acquisition systems could be utilized, with no specialized software, and individual sensors within an array can be replaced as needed. The new sensor array had small and scalable geometry and very acceptable intrinsic performance including minimal to no alteration in performance at physiologically relevant ranges of joint curvature.
    Medical Engineering & Physics 04/2011; 33(8):950-6. DOI:10.1016/j.medengphy.2011.03.004 · 1.84 Impact Factor
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    ABSTRACT: Aesthetic constraints allow dancers fewer technique modifications than other athletes to negotiate the demands of leaping. We examined vertical ground reaction force and knee mechanics during a saut de chat performed by healthy dancers. It was hypothesized that vertical ground reaction force during landing would exceed that of take-off, resulting in greater knee extensor moments and greater knee angular stiffness. Twelve dancers (six males, six females; age 18.9 ± 1.2 years, mass 59.2 ± 9.5 kg, height 1.68 ± 0.08 m, dance training 8.9 ± 5.1 years) with no history of low back pain or lower extremity pathology participated in the study. Saut de chat data were captured using an eight-camera Vicon system and AMTI force platforms. Peak ground reaction force was 26% greater during the landing phase, but did not result in increased peak knee extensor moments. Taking into account the 67% greater knee angular displacement during landing, this resulted in less knee angular stiffness during landing. In conclusion, landing was accomplished with less knee angular stiffness despite the greater peak ground reaction force. A link between decreased joint angular stiffness and increased soft tissue injury risk has been proposed elsewhere; therefore, landing from a saut de chat may be more injurious to the knee soft tissue than take-off.
    Journal of Sports Sciences 01/2011; 29(2):125-31. DOI:10.1080/02640414.2010.534807 · 2.10 Impact Factor
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    ABSTRACT: In vitro evaluation of a chemical, injectable intervention for discectomy induced destabilization. To investigate the ability of two collagen crosslinking agents to restore mechanical properties to lumbar joints destabilized by surgical decompression procedures. Posterior decompression surgery is a common procedure indicated for tissue pathology that interferes with surrounding neural structures. Previous in vitro, analytical, and clinical studies have shown that removal of load-supporting tissue can compromise joint stability mandating some form of postsurgical stabilization. Currently, no nonsurgical treatments are capable of restoring stability and preventing subsequent degeneration. Exogenous crosslinking of intact discs has shown a fourfold increase in joint stability. Fifteen bovine lumbar intervertebral joints were randomly separated into methylglyoxal or genipin treatment groups. Flexion-extension flexibility was quantified in three conditions: intact, postdecompression surgery, and after crosslinking reagent injections. Instability was quantified by calculating neutral zone (NZ), percentage of hysteresis, range of motion, and percentage of strain energy. Simulated surgical decompression increased NZ 111% (P = 0.009), 28% (P = 0.004), range of motion 57% (P = 0.003), and decreased strain energy 37% (P = 0.004). For those discs undergoing methylglyoxal treatment NZ was subsequently reduced 68% (P = 0.012), hysteresis 28% (P = 0.018), range of motion 29% (P = 0.012), and strain energy was increased 71% (P = 0.018). For discs subjected to genipin treatment, NZ was reduced 52% (P = 0.018), hysteresis 23% (P = 0.012), range of motion 44% (P = 0.017), and strain energy was increased 66% (P = 0.012). Mean NZ was lower than intact mean after both methylglyoxal and genipin treatments, 10% and 17% less, respectively, but these differences were not significant. Mean values for all other parameters posttreatment were within 6% of the corresponding intact mean values. Injections of crosslinking reagents into lumbar intervertebral discs after simulated decompression surgery restored joint stability according to all parameters. Similar results were found for genipin and methylglyoxal reagents. Implementing exogenous collagen crosslinking as an adjunct to current surgical decompression procedures may be beneficial in preventing or delaying subsequent spinal instability and degeneration.
    Spine 12/2010; 36(12):939-44. DOI:10.1097/BRS.0b013e3181e8b1d5 · 2.45 Impact Factor
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    ABSTRACT: In vitro study of genipin crosslinking effect on disc water content changes under compressive loading and unloading. To investigate the influence of collagen crosslinking on hydration and fluid flow in different regions of intact discs, and to evaluate the nutritional implications. Age-related reductions of nutrient supply and waste product removal are critically important factors in disc pathogenesis. Diffusion and fluid flow are blocked by subchondral bone thickening, cartilaginous endplate calcification, loss of hydrophilic proteoglycans, and clogging of anular pores by degraded matrix molecules. Previous studies demonstrated increased hydraulic permeability and macromolecular transport through crosslinked collagenous matrices. Genipin has also demonstrated the capability to increase retention of proteoglycans. A total of 57 bovine lumbar motion segments were divided randomly into phosphate buffered saline and 0.33% genipin-soaked treatment groups. Water content changes were measured using a mass-loss technique in 3 intervertebral disc regions following successive stages of compressive loading and unloading (post-treatment, after 1 hour 750 N compression, and after a subsequent 24-hour period of nominal loading). Net flow of fluid into or out of a region was determined from the percentage change in mean water content from successive groups. Fluid flow to and from the nucleus doubled with genipin crosslinking. Relative to the buffer-only controls, overall net fluid flow increased 103% in the nucleus pulposus, 36% in the inner anulus, and was 31% less in the outer anulus of genipin treated discs. The effects of genipin crosslinking on matrix permeability and proteoglycan retention can alter hydration levels and fluid flow in the intervertebral disc. Resulting increases in fluid flow, including a doubling of flow to and from the nucleus, could lead to enhanced nutritional inflow and waste product outflow for the disc, and may have implications for emerging cell-based therapies.
    Spine 10/2010; 35(24):E1362-6. DOI:10.1097/BRS.0b013e3181e68695 · 2.45 Impact Factor
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    ABSTRACT: Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
    ASME 2010 Summer Bioengineering Conference; 06/2010

Publication Stats

76 Citations
46.70 Total Impact Points

Institutions

  • 2011–2014
    • Michigan State University
      Ист-Лансинг, Michigan, United States
  • 2011–2013
    • Cedars-Sinai Medical Center
      • Department of Surgery
      Los Ángeles, California, United States
  • 2009–2011
    • University of California, Los Angeles
      • Department of Orthopaedic Surgery
      Los Ángeles, California, United States
  • 2006–2011
    • University of Southern California
      • Division of Biokinesiology and Physical Therapy
      Los Angeles, California, United States
  • 2010
    • National Defense Medical Center
      • Tri-Service General Hospital
      Taipei, Taipei, Taiwan