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  • Author: Lynn Snyder-Mackler x
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Lynn Snyder-Mackler

Closed kinetic chain exercise is a common component of lower extremity rehabilitation. It has virtually replaced open kinetic chain exercise in the treatment of some conditions. In this paper, anatomy and physiology as they relate to closed chain exercise are examined to elucidate its unique contributions to rehabilitation. Claims made about the specificity, functionality, and safety of closed kinetic chain exercise are discussed. Muscle action, the stretch–shortening cycle, joint position sense, and clinical cases are used to illustrate the distinct role of closed kinetic chain exercise in rehabilitation.

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Zakariya Nawasreh, David Logerstedt, Adam Marmon and Lynn Snyder-Mackler

Context: Manual perturbation training improves knee functional performance and mitigates abnormal gait in patients with anterior cruciate ligament (ACL) rupture. However, manual perturbation training is time- and labor-intensive for therapists. Objective: To investigate whether perturbation training administered using a mechanical device can provide effects similar to manual training on clinical measures and knee biomechanics after ACL rupture. Design: Prospective cohort (therapeutic) study. A 2 × 2 analysis of variance was used for statistical analysis. Setting: A clinical and biomechanical laboratory. Patients: Eighteen level I/II patients with acute ACL ruptures participated in this preliminary study. Intervention: Nine patients received mechanical perturbation training on an automated mechanical device (mechanical group), and 9 patients received manual perturbation training (manual group). Outcome Measures: Patients completed performance-based testing (quadriceps strength and single-legged hop tests), patient-reported questionnaires (Knee Outcome Survey-Activities of Daily Living Scale, Global Rating Score, and International Knee Documentation Committee 2000), and 3-dimensional gait analysis before (pretesting) and after (posttesting) training. Results: There was no significant group-by-time interaction found for all measures (P ≥ .18). Main effects of time were found for International Knee Documentation Committee 2000 (pretesting: 69.10 [10.95], posttesting: 75.14 [7.19]), knee excursion during weight-acceptance (pretesting: 16.01° [3.99°]; posttesting: 17.28° [3.99°]) and midstance (pretesting: 14.78° [4.13°]; posttesting: 16.92° [4.53°]) and external knee-flexion moment (pretesting: 0.43 [0.11] N m/kg/m; posttesting: 0.48 [0.11] N m/kg/m) (P ≤ .04). After accounting for pretesting groups’ differences, the mechanical group scored significantly higher on triple hops (mechanical: 96.73% [6.65%]; manual: 84.97% [6.83%]) and 6-m timed hops (mechanical: 102.07% [9.50%]; manual: 91.21 [9.42%]) (P ≤ .047) compared with manual group. Conclusion: The clinical significance of this study is the mechanical perturbation training produced effects similar to manual training, with both training methods were equally  effective at improving patients’ perception of knee function and increasing knee excursion and external flexion moment during walking after acute ACL rupture. Mechanical perturbation training is a potential treatment to improve patients’ functional and biomechanical outcomes after ACL rupture.

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Michael J. Axe, Thomas C. Windley and Lynn Snyder-Mackler


To design interval throwing programs for baseball players other than pitchers from 13 years of age to the college level.


The authors recorded throws to base, distance of throws, and perceived effort of throws at 4 levels of play. For catchers they also recorded number of throws to the pitcher, number of sprints to first or third base, and time in the squat stance. From these data they designed throwing programs specific to outfielders, infielders, and catchers.


No significant difference was found between the number of throws and distance of throws for infielders and catchers across all age groups. The mean distance of throws differed significantly between 13-year-olds and all other levels of play.


The authors devised 1 program for infielders and catchers of all age groups, 1 program for 13-year-old outfielders, and 1 for all other levels.

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Stephanie L. Di Stasi, Erin H. Hartigan and Lynn Snyder-Mackler

Aberrant movement strategies are characteristic of ACL-deficient athletes with recurrent knee instability (non-copers), and may instigate premature or accelerate joint degradation. Biomechanical evaluation of kinematic changes over time may elucidate noncopers’ responses to neuromuscular intervention and ACL reconstruction (ACLR). Forty noncopers were randomized into a perturbation group or a strength training only group. We evaluated the effects of perturbation training, and then gender on knee angle and tibial position during a unilateral standing task before and after ACLR. No statistically significant interactions were found. Before surgery, the strength training only group demonstrated knee angle asymmetry, but 6 months after ACLR, both groups presented with similar knee flexion between limbs. Aberrant and asymmetrical tibial position was found only in females following injury and ACLR. Neither treatment group showed distinct unilateral standing strategies following intervention; however, males and female noncopers appear to respond uniquely to physical therapy and surgery.

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Michael J. Axe, Katherine Linsay and Lynn Snyder-Mackler

The purpose of this study was to determine whether there was a relationship between knee hyperextension and intra-articular pathology in 100 consecutive patients whose sole ligament injury was an arthroscopically confirmed anterior cruciate ligament (ACL) rupture. Hyperextension of both knees was measured using a supine heel-height measurement of high reliability. There was more articular damage to the total joint, lateral joint, and lateral meniscus in patients who hyperextended than in those who did not. There was more articular damage to the total joint and medial joint in patients who were chronically ACL deficient than in those who were acutely or subacutely ACL deficient. The results demonstrate that individuals with ACL injuries whose knees hyperextend 3 cm or more sustain significantly more joint damage at the time of injury than in those whose knees hyperextend less than 3 cm. This study further defines the role of knee hyperextension in ACL injuries and offers a useful and reliable means of measuring knee hyperextension.

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Wendy I. Drechsler, John F. Knarr and Lynn Snyder-Mackler

Eighteen subjects participated in a randomized controlled clinical trial to compare the effectiveness of two physical therapy treatments for tennis elbow. The subjects were divided into two groups: In the neural tension group (NTG), the head of the radius was mobilized and specific physical therapy mobilizations were used to address hypomobility of the radial nerve. The standard treatment group (STG) received ultrasound, transverse friction massage, and stretching and strengthening exercises for the extensors of the wrist. All subjects were treated twice weekly for 6 to 8 weeks. Follow-up data were obtained at 3 months post-treatment. Subjects who received radial head mobilization improved over time (p < .05), while those who did not receive radial head mobilization did not improve. Results of the NTG treatment were linked to the radial head treatment, and isolated effects of the NTG treatment could not be determined. There were no long-term positive results in the STG.

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Michael J. Axe, Kirk H. Swigart and Lynn Snyder-Mackler

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Brian Powell, Wendy Hurd and Lynn Snyder-Mackler

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Erin H. Hartigan, Joseph Zeni Jr., Stephanie Di Stasi, Michael J. Axe and Lynn Snyder-Mackler

Less than 50% of athletes pass criteria to return to sports (RTS) 6 months after ACL reconstruction (ACLR). Using data on 38 noncopers, we hypothesized that preoperative age, quadriceps strength index (QI), and knee flexion moments (KFM) during gait would predict the ability to pass/fail RTS criteria and that preoperative quadriceps strength gains would be predictive of passing RTS criteria. Gait analysis and strength data were collected before and after a preoperative intervention and 6 months after ACLR. Age, QI, and KFM each contributed to the predictability to pass or fail RTS criteria 6 months after ACLR. Collectively, the variables predict 69% who would pass and 82% who would fail RTS criteria 6 months after ACLR. Younger athletes who have symmetrical quadriceps strength and greater KFM were more likely to pass RTS criteria. Further, 63% of those who increased preoperative quadriceps strength passed RTS criteria, whereas 73% who did not failed. Increasing quadriceps strength in noncopers before ACLR seems warranted.