Changes in Neuromuscular Coordination with Jump Training After ACL Reconstruction

Of the nearly 200,000 young athletes who undergo anterior cruciate ligament (ACL) reconstructive surgery every year in the United States, approximately half will be diagnosed with early-onset osteoarthritis within 10-15 years. Chronic impairments in mechanics and neuromuscular coordination are thought to decrease the ability of the knee to attenuate forces and accept weight during high-demand activities such as landing from a jump or hop. Specifically, decreased knee bending and a concomitant increase in co-contraction of the anterior and posterior thigh musculature are thought to increase compressive forces during landing. While brief instruction has been found to elicit a transient improvement in mechanical and neuromuscular behaviors in landing, there has been limited research into the effect of extended jump training in this population. No research has been done into the extent to which co-contraction can be modified with training, thereby ameliorating the risk of early-onset osteoarthritis. PURPOSE: To determine the effects of a best-practice jump training program on mechanical and neuromuscular behaviors in people with impaired weight acceptance following ACL reconstruction. METHODS: Twenty-five subjects completed a biomechanical screening evaluation (Wk0) of a single leg land from a 20 cm platform utilizing an 8-camera motion capture system with dual force plates. Peak vertical ground reaction force (VGRF) and peak internal extension moment during landing were both normalized to body weight (BW). They and peak knee bending in degrees served as a measure of performance. Quadriceps and hamstring recruitment were analyzed using surface electromyography (sEMG) and normalized to maximum voluntary isometric contraction. Instantaneous hamstring/quadriceps co-contraction was defined as the ratio of the two muscles multiplied by the sum of their activations with a minimum of 0 and maximum of 1. The instantaneous co-contraction was integrated over the weight acceptance phase of landing to generate a co-contraction index (CoI) with a minimum of 0 and maximum of 100. Fifteen subjects were found to have deficits in mechanical function and were enrolled in an 8-week training program. These subjects underwent twice-weekly jump training sessions, with re-testing utilizing the same protocols at mid-training (Wk4), immediately post-training (Wk8), and two months after training (Wk16). The change in kinematic and kinetic variables as well as CoI were analyzed with paired t-tests with a priori significance set to p=0.05. RESULTS: As of this writing, 14 subjects had completed Wk4 and Wk8 testing. One subject left the study after Wk4. Six had completed Wk16 testing. CoI decreased significantly with training (mean±SD; Wk0: 38.3±16.1; Wk4: 24.4±14.9 (p=0.003); Wk8: 21.3±11.3 (Wk0-Wk8 p=0.0003)). Peak knee flexion increased significantly with training as well (Wk0: 58.0°±10.9°; Wk4: 68.0°±10.1° (p=0.0004); Wk8: 73.3°±7.9° (Wk4-Wk8: p=0.037; Wk0-Wk8: p DISCUSSION: All mechanical and neuromuscular variables responded to training as expected. While jump training following ACL reconstruction has been recommended, only one other study has demonstrated its effectiveness in ameliorating mechanical risk factors for re-injury and osteoarthritis in this population. We are unaware of another study demonstrating effectiveness in changing neuromuscular behaviors that can increase compressive loads and thereby increase the risk of osteoarthritis. At this time, extensive jump training following ACL reconstruction is uncommon, with most athletes released to practice based on time from surgery or strength symmetry. These results underscore the need for more extensive rehabilitation to improve long-term outcomes for these young athletes

NRG1 functions downstream of EDS1 to regulate TIR-NLR-mediated plant immunity in Nicotiana benthamiana.

Effector-triggered immunity (ETI) in plants involves a large family of nucleotide-binding leucine-rich repeat (NLR) immune receptors, including Toll/IL-1 receptor-NLRs (TNLs) and coiled-coil NLRs (CNLs). Although various NLR immune receptors are known, a mechanistic understanding of NLR function in ETI remains unclear. The TNL Recognition of XopQ 1 (Roq1) recognizes the effectors XopQ and HopQ1 from Xanthomonas and Pseudomonas, respectively, which activates resistance to Xanthomonas euvesicatoria and Xanthomonas gardneri in an Enhanced Disease Susceptibility 1 (EDS1)-dependent way in Nicotiana benthamiana In this study, we found that the N. benthamiana N requirement gene 1 (NRG1), a CNL protein required for the tobacco TNL protein N-mediated resistance to tobacco mosaic virus, is also essential for immune signaling [including hypersensitive response (HR)] triggered by the TNLs Roq1 and Recognition of Peronospora parasitica 1 (RPP1), but not by the CNLs Bs2 and Rps2, suggesting that NRG1 may be a conserved key component in TNL signaling pathways. Besides EDS1, Roq1 and NRG1 are necessary for resistance to Xanthomonas and Pseudomonas in N. benthamiana NRG1 functions downstream of Roq1 and EDS1 and physically associates with EDS1 in mediating XopQ-Roq1-triggered immunity. Moreover, RNA sequencing analysis showed that XopQ-triggered gene-expression profile changes in N. benthamiana were almost entirely mediated by Roq1 and EDS1 and were largely regulated by NRG1. Overall, our study demonstrates that NRG1 is a key component that acts downstream of EDS1 to mediate various TNL signaling pathways, including Roq1 and RPP1-mediated HR, resistance to Xanthomonas and Pseudomonas, and XopQ-regulated transcriptional changes in N. benthamiana

Do female association preferences predict the likelihood of reproduction?

Sexual selection acting on male traits through female mate choice is commonly inferred from female association preferences in dichotomous mate choice experiments. However, there are surprisingly few empirical demonstrations that such association preferences predict the likelihood of females reproducing with a particular male. This information is essential to confirm association preferences as good predictors of mate choice. We used green swordtails (<i>Xiphophorus helleri</i>) to test whether association preferences predict the likelihood of a female reproducing with a male. Females were tested for a preference for long- or short-sworded males in a standard dichotomous choice experiment and then allowed free access to either their preferred or non-preferred male. If females subsequently failed to produce fry, they were provided a second unfamiliar male with similar sword length to the first male. Females were more likely to reproduce with preferred than non-preferred males, but for those that reproduced, neither the status (preferred/non-preferred) nor the sword length (long/short) of the male had an effect on brood size or relative investment in growth by the female. There was no overall preference based on sword length in this study, but male sword length did affect likelihood of reproduction, with females more likely to reproduce with long- than short-sworded males (independent of preference for such males in earlier choice tests). These results suggest that female association preferences are good indicators of female mate choice but that ornament characteristics of the male are also important

A picogram and nanometer scale photonic crystal opto-mechanical cavity

We describe the design, fabrication, and measurement of a cavity opto-mechanical system consisting of two nanobeams of silicon nitride in the near-field of each other, forming a so-called "zipper" cavity. A photonic crystal patterning is applied to the nanobeams to localize optical and mechanical energy to the same cubic-micron-scale volume. The picrogram-scale mass of the structure, along with the strong per-photon optical gradient force, results in a giant optical spring effect. In addition, a novel damping regime is explored in which the small heat capacity of the zipper cavity results in blue-detuned opto-mechanical damping.Comment: 15 pages, 4 figure