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  • Author: Thomas W. Kernozek x
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Tiffany Switlick, Thomas W. Kernozek and Stacey Meardon

Context:

A relationship between altered postural control and injury has been reported in sports. Sensorimotor function serves a fundamental role in postural control and is not often studied in runners. Persons who sustain running injury may have altered sensorimotor function contributing to risk of injury or reinjury.

Objectives:

To determine if differences in knee and ankle proprioception or plantar sensation exist between injured and noninjured runners.

Design:

Retrospective case-control study.

Setting:

University campus.

Participants:

Twenty runners with a history of lower-extremity overuse injury and 20 noninjured runners were examined. Injured runners were subcategorized into 2 groups based on site of injury: foot/ankle and knee/hip.

Main Outcome Measures:

Active absolute joint-repositioning error of the ankle at 20° inversion and 10° eversion and the knee at 15° and 40° flexion was assessed using an isokinetic dynamometer. Vibratory threshold at the calcaneus, arch, and great toe was determined for each subject using a handheld electric sensory threshold instrument.

Results:

Runners in the injured-foot/ankle group had increased absolute error during ankle-eversion repositioning (6.55° ± 3.58°) compared with those in the noninjured (4.04° ± 1.78°, P = .01) and the hip/knee (3.63° ± 2.2°, P = .01) groups. Runners in the injured group, as a whole, had greater sensitivity in the arch of the plantar surface (2.94 ± 0.52 V) than noninjured runners (2.38 ± 0.53 V, P = .02).

Conclusions:

Differences in ankle-eversion proprioception between runners with a history of ankle and foot injuries and noninjured runners were observed. Runners with a history of injury also displayed an increased vibratory threshold in the arch region compared with noninjured runners. Poor ankle-joint-position sense and increased plantar sensitivity suggest altered sensorimotor function after injury. These factors may influence underlying postural control and contribute to altered loading responses commonly observed in injured runners.

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Giancarlo Condello, Thomas W. Kernozek, Antonio Tessitore and Carl Foster

This study aimed to investigate biomechanical parameters during a change-of-direction task in college soccer players. Fourteen male and 12 female players performed a 10-m sprint with a 60° change of direction at 5 m. Vertical and mediolateral groundreaction force (GRF) and contact time were measured by having the subjects run in both directions while contacting a force plate with either their preferred (kicking) or nonpreferred leg. Using the midpoint between 2 pelvic markers, further parameters were evaluated: performance cutting angle and horizontal distance. Relationships between parameters, sex, and leg preference were analyzed. Significant correlations emerged between vertical and mediolateral GRF (r = .660–.909) and between contact time and performance cutting angle (r = –.598 to –.793). Sex differences were found for mediolateral GRF (P = .005), performance cutting angle (P = .043), and horizontal distance (P = .020). Leg differences were observed for vertical GRF (P = .029), performance cutting angle (P = .011), and horizontal distance (P = .012). This study showed that a sharper change of direction corresponded to a longer contact time, while no relationships were found with GRF. Moreover, measuring the angle revealed that the real path traveled was different from the theoretical one, highlighting the performance of sharper or more rounded execution. In conclusion, this study showed that specific biomechanical measurements can provide details about the execution of a change of direction, highlighting the ability of the nonpreferred leg to perform better directional changes.

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Michael Lyght, Matthew Nockerts, Thomas W. Kernozek and Robert Ragan

Achilles tendon (AT) injuries are common in runners. The AT withstands high magnitudes of stress during running which may contribute to injury. Our purpose was to examine the effects of foot strike pattern and step frequency on AT stress and strain during running utilizing muscle forces based on a musculoskeletal model and subject-specific ultrasound-derived AT crosssectional area. Nineteen female runners performed running trials under 6 conditions, including rearfoot strike and forefoot strike patterns at their preferred cadence, +5%, and –5% preferred cadence. Rearfoot strike patterns had less peak AT stress (P < .001), strain (P < .001), and strain rate (P < .001) compared with the forefoot strike pattern. A reduction in peak AT stress and strain were exhibited with a +5% preferred step frequency relative to the preferred condition using a rearfoot (P < .001) and forefoot (P=.005) strike pattern. Strain rate was not different (P > .05) between step frequencies within each foot strike condition. Our results suggest that a rearfoot pattern may reduce AT stress, strain, and strain rate. Increases in step frequency of 5% above preferred frequency, regardless of foot strike pattern, may also lower peak AT stress and strain.

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Paul F. Greene, Christopher J. Durall and Thomas W. Kernozek

Context:

A torso-elevated side support (TESS) has previously been described for measuring endurance of the lateral trunk muscles. In some individuals, however, TESS performance may be hindered by upper extremity pain or fatigue. For this reason a novel test, the feet-elevated side-support test (FESS), was examined.

Objective:

To determine intersession reliability of a FESS and a TESS on the left and right sides using a single examiner, to evaluate the relationship between tests, and to compare reasons for test termination.

Design:

Nonexperimental prospective repeated measures.

Setting:

University laboratory.

Participants:

A convenience sample of 60 healthy participants from a university community (17 men, 43 women; age 21.1 ± 2.2 y; height 169.9 ± 9.5 cm; weight 67.1 ± 11.9 kg).

Results:

Intraclass correlation coefficient between 3 testing sessions = .87 with right FESS, .86 with left FESS, .78 with right TESS, and .91 with left TESS. Pearson correlation coefficients ranged from .59 (between left FESS and left TESS in women) to .75 (between left FESS and left TESS in men). Upper extremity pain or fatigue was the reason given for test termination in 42.5% of participants during the TESS and 5.0% during the FESS (P = .000, Fisher exact test).

Conclusions:

FESS and TESS had comparable intersession reliability by the same evaluator. Moderate to high correlations were found between FESS and TESS scores, suggesting that the tests assess similar qualities. Far fewer participants terminated the FESS because of upper extremity pain or fatigue. Thus, the FESS may be a suitable alternative to the previously validated TESS, particularly for individuals with upper extremity pain or weakness.

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Christopher J. Durall, Thomas W. Kernozek, Melissa Kersten, Maria Nitz, Jonathan Setz and Sara Beck

Context:

Impaired postural control in single-limb stance and aberrant drop-landing mechanics have been implicated separately as risk factors for noncontact anterior cruciate ligament (ACL) injury, but associations between these variables has not been reported.

Objective:

To determine whether there are associations between single-limb postural control and drop-landing mechanics.

Setting:

University motion-analysis laboratory.

Design:

Single-leg-landing kinematic and kinetic data were collected after participants dropped from a hang bar. Postural-control variables COP excursion and velocity were assessed during single-leg barefoot standing on a force platform.

Participants:

A convenience sample of 24 healthy women.

Main Outcome Measures:

Pearson product–moment correlation coefficients.

Results:

Strong associations were measured between maximal knee-abduction moment and COP excursion (r = .529, P = .003) and average COP velocity (r = .529, P = .003). Strong inverse associations were measured between minimum hip-flexion angle and COP excursion (r = −.521, P = .003) and average COP velocity (r = −.519, P = .003).

Conclusions:

Participants with decreased postural control had higher knee-abduction moments and a more extended hip on landing, which have been implicated separately as risk factors for ACL injury. A longitudinal prospective analysis is needed to determine whether force-platform postural-control measures can identify athletes at risk for ACL injury.

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Andrew R. Boldt, John D. Willson, Joaquin A. Barrios and Thomas W. Kernozek

We examined the effects of medially wedged foot orthoses on knee and hip joint mechanics during running in females with and without patellofemoral pain syndrome (PFPS). We also tested if these effects depend on standing calcaneal eversion angle. Twenty female runners with and without PFPS participated. Knee and hip joint transverse and frontal plane peak angle, excursion, and peak internal knee and hip abduction moment were calculated while running with and without a 6° full-length medially wedged foot orthoses. Separate 3-factor mixed ANOVAs (group [PFPS, control] x condition [medial wedge, no medial wedge] x standing calcaneal angle [everted, neutral, inverted]) were used to test the effect of medially wedged orthoses on each dependent variable. Knee abduction moment increased 3% (P = .03) and hip adduction excursion decreased 0.6° (P < .01) using medially wedged foot orthoses. No significant group x condition or calcaneal angle x condition effects were observed. The addition of medially wedged foot orthoses to standardized running shoes had minimal effect on knee and hip joint mechanics during running thought to be associated with the etiology or exacerbation of PFPS symptoms. These effects did not appear to depend on injury status or standing calcaneal posture.

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Bryan Sorenson, Thomas W. Kernozek, John David Willson, Robert Ragan and Jordan Hove

Context:

Hip- and knee-joint kinematics during drop landings are relevant to lower-extremity injury mechanisms. In clinical research the “gold standard” for joint kinematic assessment is 3-dimensional (3D) motion analysis. However, 2-dimensional (2D) kinematic analysis is an objective and feasible alternative.

Objective:

To quantify the relationship between 2D and 3D hip and knee kinematics in single-leg drop landings and test for a set of 3D hip and knee kinematics that best predicts 2D kinematic measures during single-leg drop landings Design: Descriptive, comparative laboratory study.

Participants:

31 healthy college-age women (65.5 kg [SD 12.3], 168.1 cm [SD 6.7]).

Methods:

Participants performed five 40-cm single-leg landings during motion capture at 240 Hz. Multiple regressions were used to predict relationships for knee and hip between 2D frontal-plane projection angles (FPPA) and 3D measurements.

Results:

2D knee FPPA had a strong relationship with 3D frontal-plane knee kinematics at initial contact (IC) (r 2 = .72), which was only minimally improved with the addition of knee sagittal-plane and hip transverse-plane positions at IC (r 2 = .77). In contrast, 2D knee FPPA had a low relationship with 3D knee-abduction excursion (r 2 = .06). The addition of knee sagittal-plane and hip transverse-plane motions did not improve this relationship (r 2 = .14). 2D hip FPPA had a moderate relationship with 3D frontal-plane hip position at IC (r 2 = .52), which was strengthened with the addition of hip sagittal-plane position (r 2 = .60). In addition, hip 2D FPPA into adduction excursion had a strong association with 3D hip-adduction excursion (r 2 = .70).

Conclusion:

2D kinematics can predict 3D frontal-plane hip and knee position at IC during a single-leg landing but predict 3D frontal-plane knee excursion with far less accuracy.

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Michael A. Tabor, George J. Davies, Thomas W. Kernozek, Rodney J. Negrete and Vincent Hudson

Context:

Many clinicians use functional-performance tests to determine an athlete’s readiness to resume activity; however, research demonstrating reliability of these tests is limited.

Objective:

To introduce the Lower Extremity Functional Test (LEFT) and establish it as a reliable assessment tool.

Design:

Week 1: Subjects participated in a training session. Week 2: Initial maximal-effort time measurements were recorded. Week 3: Retest time measurements were recorded.

Setting:

The University of Wisconsin–La Crosse (UW-L) and the University of Central Florida (UCF).

Subjects:

27 subjects from UW-L and 30 from UCF.

Main Outcome Measures:

Time measurements were analyzed using intraclass correlation coefficients (ICCs).

Results:

ICC values of .95 and .97 were established at UW-L and UCF, respectively.

Conclusions:

The LEFT is a reliable assessment tool.

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Thomas W. Kernozek, Naghmeh Gheidi, Matthew Zellmer, Jordan Hove, Becky L. Heinert and Michael R. Torry

Context: Squatting is a common rehabilitation training exercise for patellofemoral pain syndrome (PFPS). Patellofemoral joint stress (PFJS) during squatting with more anterior knee displacement has not been systematically investigated. Objective: To compare PFJS during squatting using 2 techniques: squat while keeping the knees behind the toes (SBT) and squat while allowing the knees to go past the toes (SPT). Setting: University research laboratory. Participants: Twenty-five healthy females (age: 22.69 (0.74) y; height: 169.39 (6.44) cm; mass: 61.55 (9.74) kg) participated. Main Outcome Measures: Three-dimensional kinematic and kinetic data were collected at 180 and 1800 Hz, respectively. A musculoskeletal model was used to calculate muscle forces through static optimization. These muscle forces were used in a patellofemoral joint model to estimate PFJS. Results: The magnitudes of PFJS, reaction force, and quadriceps force were higher (P < .001) during SPT compared with the SBT technique. Knee flexion, hip flexion, and ankle dorsiflexion angles were reduced when using the SBT technique. Conclusions: Findings provide some general support for minimizing forward knee translation during squats for patients that may have patellofemoral pain syndrome.

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Becky L. Heinert, Thomas W. Kernozek, John F. Greany and Dennis C. Fater

Objective:

To determine if females with hip abductor weakness are more likely to demonstrate greater knee abduction during the stance phase of running than a strong hip abductor group.

Study Design:

Observational prospective study design.

Setting:

University biomechanics laboratory.

Participants:

15 females with weak hip abductors and 15 females with strong hip abductors.

Main Outcome Measures:

Group differences in lower extremity kinematics were analyzed using repeated measures ANOVA with one between factor of group and one within factor of position with a significance value of P < .05.

Results:

The subjects with weak hip abductors demonstrated greater knee abduction during the stance phase of treadmill running than the strong group (P < .05). No other significant differences were found in the sagittal or frontal plane measurements of the hip, knee, or pelvis.

Conclusions:

Hip abductor weakness may influence knee abduction during the stance phase of running.