Nathalie Alexander

Lower limb joint forces during walking on the level and slopes at different inclinations

Sloped walking is associated with an increase of lower extremity joint loading compared to level walking. Therefore, the aim of this study was to analyse lower limb joint compression forces as well as tibiofemoral joint shear forces during sloped walking at different inclinations. Eighteen healthy male participants (age: 27.0 ± 4.7 years, height: 1.80 ± 0.05 m, mass: 74.5 ± 8.2 kg) were asked to walk at a pre-set speed of 1.1m/s on a ramp (6 m × 1.5 m) at the slopes of -18°, -12°, -6°, 0°, 6°, 12° and 18°. Kinematic data were captured with a twelve-camera motion capture system (Vicon). Kinetic data were recorded with two force plates (AMTI) imbedded into a ramp. A musculoskeletal model (AnyBody) was used to compute lower limb joint forces. Results showed that downhill walking led to significantly increased hip, tibiofemoral and patellofemoral joint compression forces (p<0.05) and to significantly decreased ankle joint compression forces (p<0.05). Uphill walking significantly increased all lower limb joint compression forces with increasing inclination (p<0.05). Findings that downhill walking is a stressful task for the anterior cruciate ligament could not be supported in the current study, since anterior tibiofemoral joint shear forces did not increase with the gradient. Due to diverse tibiofemoral joint shear force patterns in the literature, results should be treated with caution in general. Finally, lower limb joint force analyses provided more insight in the structure loading conditions during sloped walking than joint moment analyses.

Comparison of Estimated and Measured Muscle Activity During Inclined Walking.

While inclined walking is a frequent daily activity, muscle forces during this activity have rarely been examined. Musculoskeletal models are commonly used to estimate internal forces in healthy populations, but these require a priori validation. The aim of this study was to compare estimated muscle activity using a musculoskeletal model with measured EMG data during inclined walking. Ten healthy male participants walked at different inclinations of 0°, ± 6°, ± 12°, and ± 18° on a ramp equipped with 2 force plates. Kinematics, kinetics, and muscle activity of the musculus (m.) biceps femoris, m. rectus femoris, m. vastus lateralis, m. tibialis anterior, and m. gastrocnemius lateralis were recorded. Agreement between estimated and measured muscle activity was determined via correlation coefficients, mean absolute errors, and trend analysis. Correlation coefficients between estimated and measured muscle activity for approximately 69% of the conditions were above 0.7. Mean absolute errors were rather high with only approximately 38% being ≤ 30%. Trend analysis revealed similar estimated and measured muscle activities for all muscles and tasks (uphill and downhill walking), except m. tibialis anterior during uphill walking. This model can be used for further analysis in similar groups of participants.

Effect of sloped walking on lower limb muscle forces

Lower limb joint loadings are increased during sloped walking compared to level walking and muscle forces are major contributors to lower limb joint forces. Therefore, the aim of this study was to analyze lower limb muscle forces during sloped walking at different inclinations. Eighteen healthy male participants (27.0±4.7y, 1.80±0.05m, 74.5±8.2kg) walked at a pre-set speed of 1.1m/s on a ramp at the inclinations of 0°, ±6°, ±12° and ±18°. Kinematic data were captured with a motion capture system and kinetic data were recorded with two force plates imbedded into the ramp. A musculoskeletal model was used to compute lower limb muscle forces (normalized to body weight and gait cycle duration). During downhill walking gluteus maximus, quadriceps, soleus, peroneus and tibialis anterior muscle forces increased (p≤0.002) compared to level walking, while gluteus minimus, piriformis, adductor, iliopsoas, hamstrings and gastrocnemii muscle forces decreased (p≤0.002). Uphill walking decreased gluteus minimus, iliopsoas and tibialis anterior muscle forces (p≤0.002), while all other muscle forces increased (p≤0.002, except gluteus medius). Joint-muscle-force waveforms provided information on possible muscle contributions to joint compression forces. The most important muscles were: gluteus medius for hip forces, quadriceps and gastrocnemii for tibiofemoral forces, quadriceps for patellofemoral forces and triceps surae for ankle forces. The contribution of each muscle changed with the inclination during sloped walking compared to level walking. The current study provided important information on muscle forces during sloped walking that can be useful for rehabilitation and training procedures.

Lower limb joint work and joint work contribution during downhill and uphill walking at different inclinations

Work performance and individual joint contribution to total work are important information for creating training protocols, but were not assessed so far for sloped walking. Therefore, the purpose of this study was to analyze lower limb joint work and joint contribution of the hip, knee and ankle to total lower limb work during sloped walking in a healthy population. Eighteen male participants (27.0±4.7yrs, 1.80±0.05m, 74.5±8.2kg) walked on an instrumented ramp at inclination angles of 0°, ±6°, ±12° and ±18° at 1.1m/s. Kinematic and kinetic data were captured using a motion-capture system (Vicon) and two force plates (AMTI). Joint power curves, joint work (positive, negative, absolute) and each joints contribution to total lower limb work were analyzed throughout the stance phase using an ANOVA with repeated measures. With increasing inclination positive joint work increased for the ankle and hip joint and in total during uphill walking. Negative joint work increased for each joint and in total work during downhill walking. Absolute work was increased during both uphill (all joints) and downhill (ankle & knee) walking. Knee joint contribution to total negative and absolute work increased during downhill walking while hip and ankle contributions decreased. This study identified, that, when switching from level to a 6° and from 6° to a 12° inclination the gain of individual joint work is more pronounced compared to switching from 12° to an 18° inclination. The results might be used for training recommendations and specific training intervention with respect to sloped walking.

Static and dynamic evaluation of a pedal system for measuring three-dimensional forces in cycling

The purpose of this study was to determine the accuracy of a newly developed pedal system (JA:Ped3) for measuring three-dimensional pedal forces in laboratory conditions in cycling. Three-dimensional force measurements were obtained using 12 strain gauges in each pedal, and the pedal angle was measured with a rotary potentiometer mounted on the pedal axle. The pedal forces were validated in a static condition by comparing a range of known forces and in dynamic conditions using the JA:Ped3 with the data collected simultaneously by two commercially available systems, SRM Powermeter and PowerForce. An incremental cycling test was performed with seven elite cyclists. In the static measurements, JA:Ped3 showed an average deviation of <2% and the maximum absolute error did not exceed 4.2 N. In the dynamic measurements, JA:Ped3-calculated pedal torque and power output yielded similar values to the corresponding data from the SRM Powermeter and showed an average deviation of <3%. Using the JA:Ped3 in a laboratory setting for testing, elite cyclists revealed plausible results. The pedal is lightweight and data transmission could be implemented to offer a device for laboratory and field measurements. This pedal would be specifically helpful for cyclists, coaches, therapists and scientists.

Effects of a leaf spring structured midsole on lower limb muscle forces in running

The current method has an accuracy that is in line with those obtained in recent studies (e.g. Preece et al., 2009), meaning a classification accuracy of over 95%. We found that jogging is the most erroneous classified activity, while running is the most accurately classified activity. It should be noted that in real-life situations, the accuracies are very likely to be lower due to disturbances, different sensor alignment, etc. In this study, the size of the confidence region was chosen large enough to cover all samples of testing data. Therefore, all the data were classified as belonging to one of the activities, as are usual for laboratory studies. When smaller confidence regions are chosen, they will not cover all the testing data samples, resulting in some samples not being classified as activity. The choice of the size of the confidence regions has a big influence on the number of samples that are classified correctly.

Does an inverted pendulum model accurately represent the gait of individuals with unilateral transfemoral amputation while walking over level ground

Background: An inverted pendulum model represents the mechanical function of able-bodied individuals walking accurately, with centre of mass height and forward velocity data plotting as sinusoidal curves, 180° out of phase. Objectives: This study investigated whether the inverted pendulum model represented level gait in individuals with a unilateral transfemoral amputation. Study Design: Controlled trial. Methods: Kinematic and kinetic data from 10 individuals with unilateral transfemoral amputation and 15 able-bodied participants were recorded during level walking. Results: During level walking, the inverted pendulum model described able-bodied gait well throughout the gait cycle, with median relative time shifts between centre of mass height and velocity maxima and minima between 1.2% and 1.8% of gait cycle. In the group with unilateral transfemoral amputation, the relative time shift was significantly increased during the prosthetic-limb initial double-limb support phase by 6.3%. Conclusion: The gait of individuals with unilateral transfemoral amputation shows deviation from a synchronous inverted pendulum model during prosthetic-limb stance. The reported divergence may help explain such individuals’ increased metabolic cost of gait. Temporal divergence of inverted pendulum behaviour could potentially be utilised as a tool to assess the efficacy of prosthetic device prescription. Clinical relevance The size of the relative time shifts between centre of mass height and velocity maxima and minima could potentially be used as a tool to quantify the efficacy of innovative prosthetic device design features aimed at reducing the metabolic cost of walking and improving gait efficiency in individuals with amputation.

Joint moments during downhill and uphill walking of a person with transfemoral amputation with a hydraulic articulating and a rigid prosthetic ankle—a case study

Introduction Functional characteristics of prosthetic ankle design may facilitate sloped walking for individuals with transfemoral (TF) amputation. The aim of the current case study was to analyze the effects of a rigid versus a hydraulically articulating ankle component on the biological joint moments of an individual with TF amputation during downhill, uphill, and level walking. Materials and Methods The gait of one individual with unilateral TF amputation, using the same prosthetic foot with rigid and hydraulic ankle components, was analyzed and compared with a control group of 18 able-bodied participants. Kinematic and kinetic data were recorded at self-selected walking speed on a sloped ramp with inclinations of −12°, −4° (downhill), 0° (level), +4°, and +12° (uphill). Results The slope influenced lower-limb joint moments similarly in both the able-bodied participants and the participant with unilateral TF amputation. The effect of altering ankle movement through exchanging prosthetic ankle componentry was most acutely seen at the hip joint of the residual limb. The use of a hydraulic ankle joint component resulted in decreased mean hip joint extension and flexion moments of up to 92% and 48%, respectively, in the residual limb when compared with the use of the rigid ankle joint component. Conclusions During sloped walking, the use of a hydraulically articulating versus rigid ankle joint component reduced the joint moments observed at the hip joint of the residual limb in an individual with unilateral TF amputation. This indicates a benefit for persons with TF amputation as the increased ankle function reduces the moment producing requirements of the hip joint, which may result in decreased energy consumption and subsequently a more efficient gait.

O 106 – Influence of ankle’s degree of freedom on muscle force estimation in different simulation environments

The main movements of the ankle joint are dorsi-, plantarflexion (DF/PF), eversion and inversion. In musculoskeletal modelling of walking, the ankle is often simplified, e.g. restricting the degree of freedom (DoF) of the ankle joint, which might lead to altered muscle force estimations. Different simulation environments use different standard anatomical models which complicates comparison between results.

Reliability of scapular kinematics estimated with three-dimensional motion analysis during shoulder elevation and flexion

BACKGROUND Knowing the reliability of three-dimensional motion analysis to evaluate scapular kinematics during upper limb movements is essential to plan further research dedicated to understanding scapulothoracic joint movements relative to the global shoulder motion. RESEARCH QUESTION The aim of this study was to assess the intra-subject as well as intra- and interrater reliability of scapulothoracic joint angles during shoulder elevation in scapular plane and shoulder flexion. METHODS Twenty healthy participants (26.6 ± 3.5 years) were asked to perform maximum shoulder elevation in scapular plane as well as shoulder flexion. Reliability was assessed using the intraclass correlation coefficient (ICC) and its 95% confidence interval of scapular kinematics (rotation, tilting, pro-retraction) at each degree of global motion (shoulder elevation or shoulder flexion) between 0° to 150°. RESULTS ICCs above 0.60 were accepted as good indicators for reliability. Intra-subject reliability was found to be very high (>0.9 for most part) for all scapulothoracic joint angles during both movements. Intra- and interrater reliability also showed good reliability being above 0.60 for the most part (except scapula tilting during shoulder elevation). Scapular kinematics showed low reliability during the respective first 10° and 20° of shoulder elevation and shoulder flexion. Furthermore, decreasing reliability was found above 120° of shoulder elevation or flexion. SIGNIFICANCE This study generally showed good to high levels of reliability in the range of interest (20-120°) in evaluating scapula kinematics in healthy adults during shoulder elevation and flexion; these results are important for future research providing a better understanding of scapular kinematics.