ISOKINETIC PEAK POWER AND PREDICTION OF PERFORMANCE

The purpose of the present study was to examine the relationship between joint peak power during isokinetic concentric knee extension and during squat vertical jump performed on a Kistler force plate. Kjnematic data from both tests were colleded. Peak power was measured as the product of angular velocity and moment at the knee joint in both tests. Rank order correlations revealed that there is no relationship between the two tests concerning the peak power output at the knee joint. It was concluded that isolated joint isokinetic tests cannot be used to predict functional performance because of the differences in muscle and joint fundion characteristics during the different movements

Strength Training for Adolescents with cerebral palsy (STAR): study protocol of a randomised controlled trial to determine the feasibility, acceptability and efficacy of resistance training for adolescents with cerebral palsy

Introduction: Gait is inefficient in children with cerebral palsy, particularly as they transition to adolescence. Gait inefficiency may be associated with declines in gross motor function and participation among adolescents with cerebral palsy. Resistance training may improve gait efficiency through a number of biomechanical and neural mechanisms. The aim of the Strength Training for Adolescents with cerebral palsy (STAR) trial is to evaluate the effect of resistance training on gait efficiency, activity and participation in adolescents with cerebral palsy. We also aim to determine the biomechanical and neural adaptations that occur following resistance training and evaluate the feasibility and acceptability of such an intervention for adolescents with cerebral palsy. Methods and analysis: 60 adolescents (Gross Motor Function Classification System level I–III) will be randomised to a 10-week resistance training group or a usual care control group according to a computer generated random schedule. The primary outcome is gait efficiency. Secondary outcomes are habitual physical activity, participation, muscle–tendon mechanics and gross motor function. General linear models will be used to evaluate differences in continuous data between the resistance training and usual care groups at 10 and 22 weeks, respectively. A process evaluation will be conducted alongside the intervention. Fidelity of the resistance training programme to trial protocol will be quantified by observations of exercise sessions. Semi structured interviews will be conducted with participants and physiotherapists following the resistance training programme to determine feasibility and acceptability of the programme. Ethics and dissemination: This trial has ethical approval from Brunel University London’s Department of Clinical Sciences’ Research Ethics Committee and the National Research Ethics Service (NRES) Committee London—Surrey Borders. The results of the trial will be submitted for publication in academic journals, presented at conferences and distributed to adolescents, families and healthcare professionals through the media with the assistance of the STAR advisory group

Identifying Robust Risk Factors for Knee Osteoarthritis Progression: An Evolutionary Machine Learning Approach

Knee osteoarthritis (KOA) is a multifactorial disease which is responsible for more than 80% of the osteoarthritis disease’s total burden. KOA is heterogeneous in terms of rates of progression with several different phenotypes and a large number of risk factors, which often interact with each other. A number of modifiable and non-modifiable systemic and mechanical parameters along with comorbidities as well as pain-related factors contribute to the development of KOA. Although models exist to predict the onset of the disease or discriminate between asymptotic and OA patients, there are just a few studies in the recent literature that focused on the identification of risk factors associated with KOA progression. This paper contributes to the identification of risk factors for KOA progression via a robust feature selection (FS) methodology that overcomes two crucial challenges: (i) the observed high dimensionality and heterogeneity of the available data that are obtained from the Osteoarthritis Initiative (OAI) database and (ii) a severe class imbalance problem posed by the fact that the KOA progressors class is significantly smaller than the non-progressors’ class. The proposed feature selection methodology relies on a combination of evolutionary algorithms and machine learning (ML) models, leading to the selection of a relatively small feature subset of 35 risk factors that generalizes well on the whole dataset (mean accuracy of 71.25%). We investigated the effectiveness of the proposed approach in a comparative analysis with well-known FS techniques with respect to metrics related to both prediction accuracy and generalization capability. The impact of the selected risk factors on the prediction output was further investigated using SHapley Additive exPlanations (SHAP). The proposed FS methodology may contribute to the development of new, efficient risk stratification strategies and identification of risk phenotypes of each KOA patient to enable appropriate interventions

Validity of the International Physical Activity Questionnaire Short Form (IPAQ-SF) as a measure of physical activity (PA) in young people with cerebral palsy

Clinical trial registration number ISRCTN90378161.© 2019 The Authors. Published by Elsevier Ltd on behalf of Chartered Society of Physiotherapy. Objectives The aim of this study was to examine the validity of the International Physical Activity Questionnaire Short Form (IPAQ-SF) as a measure of physical activity (PA) in young people with cerebral palsy (CP). Design Cross-sectional. Setting Participants were recruited through 8 National Health Service (NHS) trusts, one school, one university and through organisations that provide services for people with disabilities in England. Participants Sixty-four, ambulatory young people aged 10-19 years with CP [Gross Motor Function Classification System (GMFCS) levels I–III] participated in this study. Main outcome measure The IPAQ-SF was administered to participants. Participants were then asked to wear a wGT3X-BT triaxial accelerometer (ActiGraph, Pensacola, FL) for 7 days to objectively assess PA. Time spent in sedentary behaviour, in moderate to vigorous PA (MVPA) and in total PA (TPA) was compared between measures. Results Young people with CP self-reported less time in sedentary behaviour and underestimated the time spent in TPA,when compared to accelerometer measurements. Bland-Altman plots demonstrated poor agreement between the measures for MVPA, with upper and lower 95% limits of agreement of -147.23 to 148.9 min. After adjusting for gender and GMFCS level, age was a predictor of the difference between measures for MVPA (p < 0.001) and TPA (p < 0.001). Conclusions These findings suggest that the IPAQ-SF is not a valid method of measuring TPA or sedentary behaviour in young people with CP andit is not appropriate for use when assessing an individual’s time in MVPA. Therefore, where feasible, an objective measure of PA should be used

Stair Gait in Older Adults Worsens With Smaller Step Treads and When Transitioning Between Level and Stair Walking.

Older people have an increased risk of falling during locomotion, with falls on stairs being particularly common and dangerous. Step going (i.e., the horizontal distance between two consecutive step edges) defines the base of support available for foot placement on stairs, as with smaller going, the user's ability to balance on the steps may become problematic. Here we quantified how stair negotiation in older participants changes between four goings (175, 225, 275, and 325 mm) and compared stair negotiation with and without a walking approach. Twenty-one younger (29 ± 6 years) and 20 older (74 ± 4 years) participants negotiated a 7-step experimental stair. Motion capture and step-embedded force platform data were collected. Handrail use was also monitored. From the motion capture data, body velocity, trunk orientation, foot clearance and foot overhang were quantified. For all participants, as stair going decreased, gait velocity (ascent pA = 0.033, descent pD = 0.003) and horizontal step clearance decreased (pA = 0.001), while trunk rotation (pD = 0.002) and foot overhang increased (pA,D A D = 0.001) and their foot clearance tended to be smaller. With a walking approach, the older group (Group x Start interaction) showed a larger trunk rotation (pA = 0.011, pD = 0.015), and smaller lead foot horizontal (pA = 0.046) and vertical clearances (pD = 0.039) compared to the younger group. A regression analysis to determine the predictors of foot clearance and amount of overhang showed that physical activity was a common predictor for both age groups. In addition, for the older group, medications and fear of falling were found to predict stair performance for most goings, while sway during single-legged standing was the most common predictor for the younger group. Older participants adapted to smaller goings by using the handrails and reducing gait velocity. The predictors of performance suggest that motor and fall risk assessment is complex and multifactorial. The results shown here are consistent with the recommendation that larger going and pausing before negotiating stairs may improve stair safety, especially for older users

The human patellar tendon moment arm assessed in vivo using dual-energy X-ray absorptiometry

Accurate assessment of muscle-tendon forces in vivo requires knowledge of the muscle-tendon moment arm. Dual-energy X-ray absorptiometry (DXA) can produce 2D images suitable for visualising both tendon and bone, thereby potentially allowing the moment arm to be measured but there is currently no validated DXA method for this purpose. The aims of this study were (i) to compare in vivo measurements of the patellar tendon moment arm (d) assessed from 2D DXA and magnetic resonance (MR) images and (ii) to compare the reliability of the two methods. Twelve healthy adults (mean±SD: 31.4±9.5yr; 174.0±9.5cm; 76.2±16.6kg) underwent two DXA and two MR scans of the fully extended knee at rest. The tibiofemoral contact point (TFCP) was used as the centre of joint rotation in both techniques, and the d was defined as the perpendicular distance from the patellar tendon axis to the TFCP. The d was consistently longer when assessed via DXA compared to MRI (+3.79±1.25mm or +9.78±3.31%; P<0.001). The test-retest reliability of the DXA [CV=2.13%; ICC=0.94; ratio limits of agreement (RLA)=1.01 (*/÷1.07)] and MR [(CV=2.27%; ICC=0.96; RLA=1.00 (*/÷1.07)] methods was very high and comparable between techniques. Moreover, the RLA between the mean DXA and MRI d values [1.097 (*/÷1.061)] demonstrated very strong agreement between the two methods. In conclusion, highly reproducible d measurements can be determined from DXA imaging with the knee fully extended at rest. This has implications for the calculation of patellar tendon forces in vivo where MR equipment is not available. © 2014 Elsevier Ltd

The role of agonist and antagonist muscles in explaining isometric knee extension torque variation with hip joint angle.

PURPOSE: The biarticular rectus femoris (RF), operating on the ascending limb of the force-length curve, produces more force at longer lengths. However, experimental studies consistently report higher knee extension torque when supine (longer RF length) compared to seated (shorter RF length). Incomplete activation in the supine position has been proposed as the reason for this discrepancy, but differences in antagonistic co-activation could also be responsible due to altered hamstrings length. We examined the role of agonist and antagonist muscles in explaining the isometric knee extension torque variation with changes in hip joint angle. METHOD: Maximum voluntary isometric knee extension torque (joint MVC) was recorded in seated and supine positions from nine healthy males (30.2 ± 7.7 years). Antagonistic torque was estimated using EMG and added to the respective joint MVC (corrected MVC). Submaximal tetanic stimulation quadriceps torque was also recorded. RESULT: Joint MVC was not different between supine (245 ± 71.8 Nm) and seated (241 ± 69.8 Nm) positions and neither was corrected MVC (257 ± 77.7 and 267 ± 87.0 Nm, respectively). Antagonistic torque was higher when seated (26 ± 20.4 Nm) than when supine (12 ± 7.4 Nm). Tetanic torque was higher when supine (111 ± 31.9 Nm) than when seated (99 ± 27.5 Nm). CONCLUSION: Antagonistic co-activation differences between hip positions do not account for the reduced MVC in the supine position. Rather, reduced voluntary knee extensor muscle activation in that position is the major reason for the lower MVC torque when RF is lengthened (hip extended). These findings can assist standardising muscle function assessment and improving musculoskeletal modelling applications

Anterior Cruciate Ligament Injury: Compensation during Gait using Hamstring Muscle Activity

Previous research has shown that an increase in hamstring activation may compensate for anterior tibial transalation (ATT) in patients with anterior cruciate ligament deficient knee (ACLd); however, the effects of this compensation still remain unclear. The goals of this study were to quantify the activation of the hamstring muscles needed to compensate the ATT in ACLd knee during the complete gait cycle and to evaluate the effect of this compensation on quadriceps activation and joint contact forces. A two dimensional model of the knee was used, which included the tibiofemoral and patellofemoral joints, knee ligaments, the medial capsule and two muscles units. Simulations were conducted to determine the ATT in healthy and ACLd knee and the hamstring activation needed to correct the abnormal ATT to normal levels (100% compensation) and to 50% compensation. Then, the quadriceps activation and the joint contact forces were calculated. Results showed that 100% compensation would require hamstring and quadriceps activations larger than their maximum isometric force, and would generate an increment in the peak contact force at the tibiofemoral (115%) and patellofemoral (48%) joint with respect to the healthy knee. On the other hand, 50% compensation would require less force generated by the muscles (less than 0.85 of maximum isometric force) and smaller contact forces (peak tibiofemoral contact force increased 23% and peak patellofemoral contact force decreased 7.5% with respect to the healthy knee). Total compensation of ATT by means of increased hamstring activity is possible; however, partial compensation represents a less deleterious strategy

Variants within the MMP3 gene and patellar tendon properties in vivo in an asymptomatic population

Background/aim Gene variants encoding for proteins involved in homeostatic processes within tendons may influence its material and mechanical properties in humans. The purpose of this study was to examine the association between three polymorphisms of the MMP3 gene, (rs679620, rs591058 and rs650108) and patellar tendon dimensional and mechanical properties in vivo. Methods One hundred and sixty, healthy, recreationally-active, Caucasian men and women, aged 18–39 were recruited. MMP3 genotype determined using real-time PCR was used to select 84 participants showing greatest genetic differences to complete phenotype measurements. Patellar tendon dimensions (volume) and functional (elastic modulus) properties were assessed in vivo using geometric modelling, isokinetic dynamometry, electromyography and ultrasonography. Results No significant associations were evident between the completely linked MMP3 rs591058 and rs679620 gene variants, and closely linked rs650108 gene variant, and either patellar tendon volume (rs679620, P = 0.845; rs650108, P = 0.984) or elastic modulus (rs679620, P = 0.226; rs650108, P = 0.088). Similarly, there were no associations with the Z-score that combined those dimension and functional properties into a composite value (rs679620, P = 0.654; rs650108, P = 0.390). Similarly, no association was evident when comparing individuals with/without the rarer alleles (P > 0.01 in all cases). Conclusions Patellar tendon properties do not seem to be influenced by the MMP3 gene variants measured. Although these MMP3 gene variants have previously been associated with the risk of tendon pathology, that association is unlikely to be mediated via underlying tendon dimensional and functional properties

Near-source pulse-like seismic demand for multi-linear backbone oscillators

Nonlinear static procedures, which relate the seismic demand of a structure to that of an equivalent single-degree-of-freedom (SDOF) oscillator, are well-established tools in the performance based earthquake engineering framework and have gradually found their way into modern codes for seismic design and assessment. Initially, such procedures made recourse to inelastic spectra derived for simple elastic-plastic or bilinear oscillators, but the request for demand estimates, which delve deeper into the inelastic range, shifted the trend towards inves-tigating the seismic demand of oscillators with more complex backbone curves. Meanwhile, the engineering relevance of near-source (NS) pulse-like ground motions has been receiving increased attention, since it has been recognized that such ground motions can induce a distinctive type of inelastic demand. Pulse-like NS ground motions are usually the result of rupture directivity, where seismic waves generated at different points along the rupture front arrive at a site at the same time, leading to a double-sided velocity pulse, which delivers most of the seismic energy. Recent research has led to a methodology being proposed for incorpo-rating this NS effect in the implementation of nonlinear static procedures. Both of the aforementioned lines of earthquake engineering research motivate the present study, which investigates the ductility demands imposed by pulse-like NS ground motions on SDOF oscillators who feature pinching hysteretic behavior with trilinear backbone curves. This in-vestigation uses incremental dynamic analysis (IDA) considering a suite of one hundred and thirty pulse-like-identified ground motions. Median, as well as 16% and 84% fractile, IDA curves are calculated, on which an analytical model is fitted. Least-squares estimates are ob-tained for the model parameters, which importantly include pulse period Tp. The resulting equa-tions effectively constitute an R-μ-T/Tp relation for pulse-like NS motions. A potential application of this result is briefly demonstrated in an illustrative example of NS seismic de-mand estimation