The Two-Dimensional Relationship Between Ground Reaction Force Vector and Knee Axis of Rotation Reflect Knee Loading Deficits During Squatting Post-ACLr

PURPOSE Individuals post-anterior cruciate ligament reconstruction (ACLr) perform reduced knee extensor moments (KEM) during squats by shifting weight to the non-surgical (NSx) limb 1 or by shifting demands from the knee to hip 1,2. These compensations occur without observable differences in joint angles by small adjustments in the center of pressure (COP). This makes them difficult to detect and may contribute to their persistence. Differences between limbs in COP position suggest that individuals adjust the relationship of the ground reaction force vector (GRFv) relative to the joint center to redistribute the loading demands in the surgical limb 3. Recent technology allows for two-dimensional video assessment of this relationship and may provide more accessible means to identify knee loading deficits. The purpose of this study is to determine if the between-limb difference in the two-dimensional distance between the GRFv and knee joint axis of rotation and the GRF magnitude will predict a between limb difference in knee extensor moment in a squat. METHODS Twenty-two individuals (age: 25.7 ± 10.3 years) 110 ± 18 days following ACLr participated. Kinematic and kinetic data were collected (3D motion capture system, force platforms) while bilateral squats were performed to self-selected depth. Joint moments were calculated using standard inverse dynamics equations. The horizontal distance from a marker placed over the lateral epicondyle of the knee and the GRFv, peak KEM and GRFv magnitude were calculated at the instance of KEM. Ratios Sx/NSx were calculated for all variables to reflect difference between limbs. Multiple linear regression assessed the influence of the horizontal distance and GRFv magnitude ratio on KEM ratio. RESULTS Together, between-limb ratios of horizontal distance and GRF magnitude explained 81.4% of the variance in KEM ratio. Horizontal distance ratio explained 61% of the variance and GRF ratio an additional 21.4% of the variance of KEM ratio. CONCLUSIONS Combination of GRF and the horizontal distance between the GRFv and knee axis of rotation in the sagittal plane provides good information about knee extensor loading deficits. This relationship suggests that these variables may allow for estimations of KEM deficits during a squat in individuals post-ACLr. REFERENCES 1. Sigward SM, Chan MSM, Lin PE, Almansouri SY, Pratt KA. Compensatory strategies that reduce knee extensor demand during a bilateral squat change from 3 to 5 months following anterior cruciate ligament reconstruction. Journal of Orthopaedic and Sports Physical Therapy. 2018;48(9):713-718. doi:10.2519/jospt.2018.7977 2. Salem GJ, Salinas R, Harding FV. Bilateral kinematic and kinetic analysis of the squat exercise after anterior cruciate ligament reconstruction. Arch Phys Med Rehabil. 2003;84(8):1211-1216. doi:10.1016/S0003-9993(03)00034-0 3. Chan MS, Sigward SM. Center of pressure predicts Intra-limb compensatory patterns that shift demands away from knee extensors during squatting. J Biomech. 2020;111(2020):110008. doi:10.1016/j.jbiomech.2020.11000

Individuals Following Anterior Cruciate Ligament Reconstruction Respond Differently To Limb Loading Instruction: A Clustering Analysis

Individuals following anterior cruciate ligament reconstruction (ACLr) demonstrate altered loading strategies such as shifting mechanical demand away from the surgical knee. Previous work found that individuals can restore limb loading symmetry with instruction to equalize weight distribution between limbs during a squat task. However, when looking at individual responses to these instructions, it appear that not all individual responded similarly. PURPOSE: To use k-means clustering to describe the variation in response to instruction to equalize weight between limbs in individuals 3-4 months post-ACLr. METHODS: We performed a secondary analysis of a dataset including two groups: individuals 110.4 days (18.4 days) post-anterior cruciate ligament reconstruction (ACLr; n = 20) and healthy matched controls (CTRL; n = 19). Kinematic and kinetic data were collected (3D motion capture system, force platforms) while participants performed squats in natural (no instruction; N) and instructed (instructed to evenly distribute their weight between limbs; IN) conditions. Limb and knee loading symmetry were calculated as the ratio of vertical ground reaction force and knee extensor moment impulse, respectively, between surgical (Sx):matched and non-surgical (non-Sx):matched limbs (ACLr:control). K-means clustering created three clusters based on natural and instructed LLS and KLS and the between condition difference of LLS and KLS. RESULTS: Three clusters were defined describing various responses to limb loading instruction: 1) non-responders, 2) symmetrical responders, and 3) overloading responders. A random forest algorithm was used to find the most influential variables and identified natural KLS to be the most important variable in clustering. CONCLUSION: Only 20% of participants in our sample of individuals following ACLr improved knee loading to be symmetrical when given instruction to equalize weight between limbs. This instruction may not be effective in restoring knee loading in the post-ACLr population

Suppression of Dwarf Galaxy Formation by Cosmic Shocks

We carry out a numerical study of the effects of supernova-driven shocks on galaxy formation at z=9. These "cosmic explosions" can have a significant impact on galaxies forming nearby. We study such interactions in two key cases. In the first case in which the forming galaxy has already virialized, the impinging shock has only a small effect (< 1% of the gas is removed) and star formation continues relatively unimpeded. However, in the second case in which the nearby forming galaxy is at the more diffuse turn-around stage, a large fraction (~70%) of the gas is stripped away from the host dark-matter halo and ejected into the intergalactic medium. As the time spent near turn-around is much longer than the interval from virialization to galaxy formation due to strong radiative losses, we expect the second case to be more representative of the majority of outflow-galaxy interactions. Thus SN-driven pregalactic outflows may be an efficient mechanism for inhibiting the formation of neighbouring galaxies at high redshift. We briefly outline the possible cosmological consequences of this effect.Comment: 11 pages, 6 figures, accepted for publication in MNRA

Editorial: Neuromuscular diagnostics and sensorimotor performance in training and therapy: beyond the pure biomechanical approach

Traditional movement science research has adopted methodology that describes differences in movement among groups or conditions using biomechanical variables to infer underlying features of neuromuscular control. Historically, this approach marked the onset of the complex analysis of movement biomechanics bring relevant insights into the mechanics of human movement (1). Hypotheses were developed by extrapolating data from healthy active to injured populations (2). The last decade before the millennium provided first references to the neuromechanical aspects of movement, thus expanding the view towards the neuromotor control aspect of movement generation and adjustment (3). In the 2000s, substantial evidence is reported on spinal and supraspinal adaptations after balance or sensorimotor training which delivered important evidence-based knowledge that was rapidly implemented in clinical practice (4). Moreover, studies that combined both “mechanical” and “neuromuscular” views evolved (5, 6). We can postulate, that we still need more evidence-based knowledge on the interplay between the underlying neurophysiologic movement generation and the observed mechanical motor output. These integral neuro-biomechanical approaches still rely heavily on a biomedical perspective that is lately challenged by the call for biopsychosocial paradigms to cover all relevant aspects in human movement analysis to draw meaningful conclusions for diagnostics, prevention and therapy (7). Research can rarely incorporate all dimensions at one time but our claim should be that we focus on experimental paradigms that purposely integrate both biomechanical and neuromechanical pieces of the puzzle to seek a more comprehensive understanding of typical and impaired movement. There are promising examples of such approaches that now combine classic biomechanical research with neurophysiological methods and patient reported outcomes or other psychometric measures (8, 9). The aim of this Research Topic is therefore to provide a collection of studies that contribute to these integrative approaches by using diverse viewpoints and subsequently diverse methodology from study protocols, scoping or systematic reviews or experimental and interventional studies. They all contribute with different pieces of the puzzle “beyond the pure biomechanical approach”. Three investigations provided insight into motor control and muscle coordination in patient populations and those with experimentally imposed pian. Bartsch-Jimenez et al. described differences in “fine synergies” derived from electromyographic data of multiple lower leg muscles between persons with foot drop and controls that may reflect potentially relevant for motor adaptations to impaired ankle control. Chan and Sigward found that achieving loading symmetry in standing requires attention in those who are recovering from ACL reconstruction while it is more automatic in healthy controls. Bertrand-Charette et al. described the influence of acute ankle pain on motor output and performance of a standard balance test used to assess function in individuals with ankle injuries. While these studies targeted specific adaptations, Quarmby et al.’s systematic review of evidence regarding mechanical and neuromuscular control impairments in individuals with Achilles tendinopathy highlights limited consensus and areas for future work. Other contributors provided insight into the effects of neurocognitive and neurophysiological based interventions. Rogan and Taeymans describe in their systematic review the evidence of positive effects of whole-body vibration on sensorimotor function in the elderly which highlights the therapeutic potential in this population. Faes et al. investigated the effects of a whole-body vibration intervention on several dimensions like movement control, well-being, and cognition in a randomized controlled trial. Hegi et al. summarized the existing body of evidence on sensor-based augmented visual feedback that should be used in coordination training to elicit sensorimotor adaptations. Mourits et al. describe a study protocol of a quasi-randomized controlled trial investigation of a game based intervention that combines neurocognitive effects of an external focus of attention and game like motivation along with patient specific real time spine motion to improve movement control of the spine. Finally, Mathieu-Kälin et al. described an assessment tool for develop to measure movement quality during hop tests. This tool adds important valuation of the control strategies used to complete a task beyond that of just performance. The goal of the Research Topic was accomplished by presenting studies that incorporated a variety of manscirpt that represent “out of the box” neuro-biomechanical approaches to investigate underlying features of impaired movement. The broad range of paradigms and methodological approaches of the Research Topic certainly reflects the initial idea and the contributions highlight different aspects on the pathway to more mutifaceted approaches. The guest editor team would love to see many views, downloads, and citations of the papers included in this Research Topic and we anticipate that in the future more contributions to Frontiers and Sports and Active living could be “virtually” added to this topic

Validation of Vertical Force Measures During Hop Tasks Using Pressure Insoles

Assessment of vertical ground reaction forces (vGRF) during jumping and landing tasks is commonly used as a tool to quantify limb loading following injury. While embedded force plates are the current gold standard, cost and poor ecological validity limit their feasibility for assessment of loading during sport agility tasks. Wearable pressure insoles can measure plantar pressure wirelessly and may provide an alternative for on-field assessments. Previous studies have assessed the validity of insoles with varying results. Few studies have considered tasks that require both vertical and horizontal forces similar to those required for agility tasks. This may have important implications for clinical use outside the laboratory setting. PURPOSE: Determine concurrent validity of pressure insole and forceplates for measuring vertical loading force during hop tasks. METHODS: Fifteen healthy individuals (females=9, age 26.6 ± 3.1 yrs.; 1.7 ± 0.1 m; 72 ± 15.8 kg) participated. Force data was collected concurrently from triaxial force plates (AMTI, 1500 Hz) and pressure insoles (Moticon OpenGo, 25Hz) during single limb stance (SLS), forward hop (FH) and lateral hop (LH) tasks. Impulse (N·s) was calculated as the area under the vertical force time curve for each limb during the stance phase. Impulse was normalized to body weight (force averaged across 3 seconds during SLS) for FH and LH. Three trials per task were used to examine the relationship (Pearson correlation) and agreement (ICC 2,2) between methods. RESULTS: Impulse from insoles was positively related to force plates during SLS (r= .71, p\u3c.05), FH (r=.85, p\u3c.05), and LH (r=.89, p\u3c.05). ICC were SLS (.32 p\u3c.05), FH (.83 p\u3c.05) and LH (.89 p\u3c.05). Average relative differences were SLS -290.92 (200.94) N·s, FH .004 (.13) N·s/N-BW, and LH .006 (.08) N·s/N-BW. CONCLUSION: Fair ICC during SLS suggest that force measures from insoles and force plates have poor agreement. However, after normalizing by body weight, vertical force from insoles and force plates were highly correlated and showed excellent agreement. These data suggest that insoles provide similar information to force plates during forward and lateral hops. The magnitude of relative difference between instruments should be considered when interpreting data for each use case

Altered Dynamic Postural Control during Step Turning in Persons with Early-Stage Parkinson's Disease

Persons with early-stage Parkinson's disease (EPD) do not typically experience marked functional deficits but may have difficulty with turning tasks. Studies evaluating turning have focused on individuals in advanced stages of the disease. The purpose of this study was to compare postural control strategies adopted during turning in persons with EPD to those used by healthy control (HC) subjects. Fifteen persons with EPD, diagnosed within 3 years, and 10 HC participated. Participants walked 4 meters and then turned 90°. Dynamic postural control was quantified as the distance between the center of pressure (COP) and the extrapolated center of mass (eCOM). Individuals with EPD demonstrated significantly shorter COP-eCOM distances compared to HC. These findings suggest that dynamic postural control during turning is altered even in the early stages of PD

Sex variation in patellar tendon kinetics during running

Purpose. The aim of the current investigation was to determine whether female recreational runners exhibit distinct patellar tendon loading patterns in relation to their male counterparts. Methods. Twelve male (age 26.55 ± 4.11 years, height 1.78 ± 0.11 m, mass 77.11 ± 5.06 kg) and twelve female (age 26.67 ± 5.34 years, height 1.67 ± 0.12 m, mass 63.28 ± 9.75 kg) runners ran over a force platform at 4.0 m · s –1. Lower limb kinematics were collected using an eight-camera optoelectric motion capture system which operated at 250 Hz. Patellar tendon loads were examined using a predictive algorithm. Sex differences in limb, knee and ankle joint stiffness were examined statistically using independent samples t tests. Results. The results indicate that patellar tendon force (male = 6.49 ± 2.28, female = 7.03 ± 1.35) and patelllar tendon loading rate (male = 92.41 ± 32.51, female = 111.05 ± 48.58) were significantly higher in female runners. Conclusions. Excessive tendon loading in female runners indicates that female runners may be at increased risk of patellar tendon pathologies

How reliable are knee kinematics and kinetics during side-cutting manoeuvres?

INTRODUCTION: Side-cutting tasks are commonly used in dynamic assessment of ACL injury risk, but only limited information is available concerning the reliability of knee loading parameters. The aim of this study was to investigate the reliability of side-cutting data with additional focus on modelling approaches and task execution variables. METHODS: Each subject (n=8) attended six testing sessions conducted by two observers. Kinematic and kinetic data of 45° side-cutting tasks was collected. Inter-trial, inter-session, inter-observer variability and observer/trial ratios were calculated at every time-point of normalised stance, for data derived from two modelling approaches. Variation in task execution variables was regressed against that of temporal profiles of relevant knee data using one-dimensional statistical parametric mapping. RESULTS: Variability in knee kinematics was consistently low across the time-series waveform (≤5°), but knee kinetic variability was high (31.8, 24.1 and 16.9Nm for sagittal, frontal and transverse planes, respectively) in the weight acceptance phase of the side-cutting task. Calculations conveyed consistently moderate-to-good measurement reliability. Inverse kinematic modelling reduced the variability in sagittal (∼6Nm) and frontal planes (∼10Nm) compared to direct kinematic modelling. Variation in task execution variables did not explain any knee data variability. CONCLUSION: Side-cutting data appears to be reliably measured, however high knee moment variability exhibited in all planes, particularly in the early stance phase, suggests cautious interpretation towards ACL injury mechanics. Such variability may be inherent to the dynamic nature of the side-cutting task or experimental issues not yet known