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Christopher A. Knight, Adam R. Marmon and Dhiraj H. Poojari

Subjects learned to produce brief isometric force pulses that were 10% of their maximal voluntary contraction (MVC) force. Subjects became proficient at performing sets of 10 pulses within boundaries of 8–12% MVC, with visual feedback and without (kinesthetic sense). In both the control (Con, n = 10) and experimental (Exp, n = 20) groups, subjects performed two sets of 10 kinesthetically guided pulses. Subjects then either performed a 10-s MVC (Exp) or remained at rest (Con) between sets. Following the MVC, Exp subjects had force errors of +30%, whereas performance was maintained in Con. There was evidence for both muscular and neural contributions to these errors. Postactivation potentiation resulted in a 40% gain in muscle contractility (p = .003), and there was a 26% increase in the neural stimulation of muscle (p = .014). Multiple regression indicated that the change in neural input had a stronger relationship with force errors than the increased contractility.

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Nancy Getchell, Samuel J. Mackenzie and Adam R. Marmon

This study examined the effect of short-term auditory pacing practice on dual motor task performance in children with and without dyslexia. Groups included dyslexic with Movement Assessment Battery for Children (MABC) scores > 15th percentile (D_HIGH, n = 18; mean age 9.89 ± 2.0 years), dyslexic with MABC ≤ 15th percentile (D_LOW, n = 15; mean age 10.43 ± 1.8 years), and typically developing (TD, n = 18; mean age 10.64 ± 1.8 years). Participants clapped and walked simultaneously for 3 pretest trials, completed 16 trials with auditory pacing, and 3 posttest trials without pacing. D_LOW differed significantly from D_HIGH and TD in mean relative phase (MRP) of the clap relative to the step, and variability (VRP) of the MRP. Significant differences also existed between pretest blocks and all other blocks in MRP. The results suggest that a short-term auditory pacing may be effective in improving MRP in all children. Further, there may be subtypes of dyslexia wherein children have more profound coordination difficulties and may preferentially change dual motor task performance with auditory pacing.

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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.