Automatic identification of gait events using an instrumented sock

Background: textile-based transducers are an emerging technology in which piezo-resistive properties of materials are used to measure an applied strain. By incorporating these sensors into a sock, this technology offers the potential to detect critical events during the stance phase of the gait cycle. This could prove useful in several applications, such as functional electrical stimulation (FES) systems to assist gait. Methods: we investigated the output of a knitted resistive strain sensor during walking and sought to determine the degree of similarity between the sensor output and the ankle angle in the sagittal plane. In addition, we investigated whether it would be possible to predict three key gait events, heel strike, heel lift and toe off, with a relatively straight-forward algorithm. This worked by predicting gait events to occur at fixed time offsets from specific peaks in the sensor signal. Results: our results showed that, for all subjects, the sensor output exhibited the same general characteristics as the ankle joint angle. However, there were large between-subjects differences in the degree of similarity between the two curves. Despite this variability, it was possible to accurately predict gait events using a simple algorithm. This algorithm displayed high levels of trial-to-trial repeatability. Conclusions: this study demonstrates the potential of using textile-based transducers in future devices that provide active gait assistance

Is there a minimum complexity required for the biomechanical modelling of running?

Mathematical models have the potential to provide insight into human running. Existing models can be categorised as either simple or complex, and there appears to be a lack of natural progression in model development. By sequentially adding complexity, there is the potential to determine how different mechanical components contribute to the biomechanics of running. In this study, a series of four models, of increasing complexity were developed in OpenSim: a simple spring-mass model, a two-segment model with a torsional spring at the knee and two three-segment models, one with a sprung knee and ankle and another with a sprung knee and actuated ankle. For each model, a forward simulation was developed and model predictions compared with experimental data from 10 forefoot runners. The results showed the spring-mass model overestimated the vertical displacement of the centre of mass (percentage difference: 43.6(22.4)-67.7(21.7)%) and underestimated the vertical ground reaction force (percentage difference: 13.7(8.9)-34.4(10.9)%) compared to the experimental data. Adding a spring at the knee increased the match with the vertical centre of mass displacement (percentage difference: 4.4(25.2)-18.4(40.2)%), however, geometry restrictions meant it was only possible to model approximately 60% of stance. The passive three-segment model showed a good match with centre of mass movements across most of stance (percentage difference in the vertical centre of mass displacement: 4.3(24.5)-21.3(19.2)%), however, actuation at the ankle was required to obtain a closer match with experimental kinetics and joint trajectories (e.g. vertical ground reaction force RMSD decreased by approximately 0.4BW). This is the first study to investigate models of increasing complexity of distance running. The results show that agreement between experimental data and model simulations improves as complexity increases and this provides useful insight into the mechanics of human running

The biomechanical characteristics of high-performance endurance running

The biomechanical profile of high-level endurance runners may represent a useful model that could be used for developing training programmes designed to improve running style. This study, therefore, sought to compare the biomechanical characteristics of high-performance and recreational runners. Kinematic and kinetic measurements were taken during overground running from a cohort of 14 high-performance (8 male) and 14 recreational (8 male) runners, at four speeds ranging from 3.3 to 5.6 m s−1. Two-way ANOVA analysis was then used to explore group and speed effects and principal component analysis used to explore the interdependence of the tested variables. The data showed the high-performance runners to have a gait style characterised by an increased vertical velocity of the centre of mass and a flight time that was 11% longer than the recreational group. The high-performance group were also observed to adopt a forefoot strike pattern, to contact the ground with their foot closer to their body and to have a larger ankle moment. Importantly, although observed group differences were mostly independent of speed, the tested variables showed a high degree of interdependence suggesting an underlying unitary phenomenon. This is the first study to compare high-performance and recreational runners across a full range of kinematic and kinetic variables. The results suggest that high-performance runners maintain stride length with a prolonged aerial phase, rather than by landing with a more extended knee. These findings motivate future intervention studies that should investigate whether recreational runners could benefit from instruction to decrease shank inclination at foot contact

A marker set for measuring the kinematics of the lumbar spine and thoracic spine during running : a technical note

A protocol for tracking the motion of the lumbar spine, which uses seven skin mounted markers, has been adopted in previous studies investigating running. However, this configuration of can be difficult to track with passive motion capture systems. This study therefore investigated whether a four-marker configuration could accurately reproduce the pose of the lumbar spine obtained using the seven-marker configuration. The study also investigated two methods of tracking the thorax. The first method consisted of markers attached to the sterum and the second used two markers placed bilaterally over the acromioclavicular joints and another on the posterior thoracic spine. Kinematic data was collect for n=15 male subjects and the pose, calculated using the different tracking configurations, compared for both the lumbar spine and thoracic spine. The results demonstrated a good match between two lumbar tracking marker sets. However, there was considerable difference between the two thoracic markers sets which was likely due to movement of the arms influencing the pose of the thorax. We therefore recommend the use of four makers to track the motion of the lumbar spine and a rigid plate, mounted at the top of the sternum, to track motion of the thoracic spine during running

Variation in pelvic morphology may prevent the identification of anterior pelvic tilt

Pelvic tilt is often quantified using the angle between the horizontal and a line connecting the anterior superior iliac spine (ASIS) and the posterior superior iliac spine (PSIS). Although this angle is determined by the balance of muscular and ligamentous forces acting between the pelvis and adjacent segments, it could also be influenced by variations in pelvic morphology. The primary objective of this anatomical study was to establish how such variation may affect the ASIS-PSIS measure of pelvic tilt. In addition, we also investigated how variability in pelvic landmarks may influence measures of innominate rotational asymmetry and measures of pelvic height. Thirty cadaver pelves were used for the study. Each specimen was positioned in a fixed anatomical reference position and the angle between the ASIS and PSIS measured bilaterally. In addition, side-to-side differences in the height of the innominate bone were recorded. The study found a range of values for the ASIS-PSIS of 0–23 degrees, with a mean of 13 and standard deviation of 5 degrees. Asymmetry of pelvic landmarks resulted in side-to-side differences of up to 11 degrees in ASISPSIS tilt and 16 millimeters in innominate height. These results suggest that variations in pelvic morphology may significantly influence measures of pelvic tilt and innominate rotational asymmetry

Trunk flexion during walking in people with knee osteoarthritis

BACKGROUND:Over 50% of the body's mass is concentrated within the head, arms and trunk. Thus, small deviations in the orientation of the trunk, during normal walking, could influence the position of the centre of mass relative to the lower limb joint centres and impact on lower limb biomechanics. However, there are minimal data available on sagittal kinematics of the trunk in people with knee osteoarthritis (OA) during walking.RESEARCH QUESTION:Do people with knee OA have altered kinematic patterns of the trunk, pelvis or hip compared with healthy control participants during walking?METHODS:Statistical parametric mapping was used to compare sagittal and frontal plane kinematic patterns, during walking, between a healthy group and cohort of people with knee OA.RESULTS:Individuals with knee OA walked with a mean increase in trunk flexion of 2.6°. Although this difference was more pronounced during early stance, it was maintained across the whole of stance phase. There were no differences, between the groups, in sagittal plane pelvic or hip kinematics. There were also no differences in trunk, pelvic or hip kinematics in the frontal plane.SIGNIFICANCE:Most previous gait research investigating trunk motion in people with knee OA has focused on the frontal plane. However, our data suggest that an increase in sagittal trunk flexion may be a clinical hallmark of people with this disease. Altered trunk flexion could affect joint moments and muscle patterns and therefore our results motivate further research in this area

Reproducibility of kinematic measures of the thoracic spine, lumbar spine and pelvis during fast running

This study evaluated the reproducibility of the angular rotations of the thoracic spine, lumbar, spine, pelvis and lower extremity during running. In addition, the study compared kinematic, reproducibility between two methods for calculating kinematic trajectories: a six degrees of freedom, (6DOF) approach and a global optimisation (GO) approach. With the first approach segments were, treated independently, however with GO approach joint constraints were imposed to stop translation, of adjacent segments. A total of 12 athletes were tested on two separate days whilst running over, ground at a speed of 5.6ms-1. The results demonstrated good between-day reproducibility for most, kinematic parameters in the frontal and transverse planes with typical angular errors of 1.4-3°., Acceptable repeatability was also found in the sagittal plane. However, in this plane, although, kinematic waveform shape was preserved between testing session, there were sometimes shifts in, curve offset which lead to slightly higher angular errors, typically ranging from 1.9-3.5°. In general, the, results demonstrated similar levels of reproducibility for both computational approaches (6DOF and, GO) and therefore suggest that GO may not lead to improved kinematic reproducibility during running

A 10% increase in step rate improves running kinematics and clinical outcomes in runners with patellofemoral pain at 4 weeks and 3 months

Background: Aberrant frontal plane hip and pelvis kinematics have been frequently observed in runners with patellofemoral pain (PFP). Gait retaining interventions have been shown to improve running kinematics and may therefore be beneficial in runners with PFP. Purpose: the aim of this study was to investigate whether a 10% increase in running step rate influences frontal plane kinematics of the hip and pelvis, as well as clinical outcomes in runners with PFP. Study Design: Case Series Methods: Runners with PFP underwent a 3D gait analysis to confirm the presence of aberrant frontal plane hip and pelvis kinematics at baseline. Twelve participants with frontal plane hip and pelvis kinematics one standard deviation above a reference database, were invited to participate in the gait retraining intervention. Running kinematics along with clinical outcomes of pain and functional measures were recorded at baseline, 4 weeks following retraining and 3-months. Gait retraining consisted of a single session where step rate was increased by 10% using an audible metronome. Participants were asked to continue their normal running while self-monitoring their step rate using a global positioning system watch and audible metronome. Results: Following gait retraining significant improvements in running kinematics and clinical outcomes were observed at 4 week and 3-month follow up. Repeated measures ANOVA with post hoc Bonferroni (p <0.016) showed significant reductions in peak contralateral pelvic drop (Mean Difference [MD], 3.12⁰; 95% Confidence Interval [CI], 1.88⁰, 4.37⁰), hip adduction (MD, 3.99⁰; 95% CI, 2.01⁰, 5.96⁰) and knee flexion (MD, 4.09⁰; 95% CI, 0.04⁰, 8.15⁰), as well as significant increases in self-reported weekly running volume (MD, -13.78km; 95% CI, -22.93km, -4.62km) and longest run pain free (MD, -6.84km; 95% CI, -10.62km, -3.05km). Friedman test with post hoc Wilcoxon signed-rank showed significant improvements in Numerical Rating Scale for worst pain in the past week and Lower Extremity Functional Scale. Conclusion: A single session of gait retraining using a 10% increase in step rate results in significant improvements in running kinematics, pain and function in runners with PFP. These improvements were maintained at 3-month follow up. It is important to assess for aberrant running kinematics at baseline to ensure gait interventions are targeted appropriately. Clinical Relevance: Step rate modification is a simple method of gait retraining that can be easily integrated into clinical practice and running outside of a laboratory setting