Patric Eichelberger

Analysis of accuracy in optical motion capture – A protocol for laboratory setup evaluation

Validity and reliability as scientific quality criteria have to be considered when using optical motion capture (OMC) for research purposes. Literature and standards recommend individual laboratory setup evaluation. However, system characteristics such as trueness, precision and uncertainty are often not addressed in scientific reports on 3D human movement analysis. One reason may be the lack of simple and practical methods for evaluating accuracy parameters of OMC. A protocol was developed for investigating the accuracy of an OMC system (Vicon, volume 5.5×1.2×2.0m(3)) with standard laboratory equipment and by means of trueness and uncertainty of marker distances. The study investigated the effects of number of cameras (6, 8 and 10), measurement height (foot, knee and hip) and movement condition (static and dynamic) on accuracy. Number of cameras, height and movement condition affected system accuracy significantly. For lower body assessment during level walking, the most favorable setting (10 cameras, foot region) revealed mean trueness and uncertainty to be -0.08 and 0.33mm, respectively. Dynamic accuracy cannot be predicted based on static error assessments. Dynamic procedures have to be used instead. The significant influence of the number of cameras and the measurement location suggests that instrumental errors should be evaluated in a laboratory- and task-specific manner. The use of standard laboratory equipment makes the proposed procedure widely applicable and it supports the setup process of OCM by simple functional error assessment. Careful system configuration and thorough measurement process control are needed to produce high-quality data.

Pelvic floor muscle reflex activity during coughing – an exploratory and reliability study

OBJECTIVES Activities that provoke stress urinary incontinence (SUI) rapidly increase the intra-abdominal pressure and the impact loading on the pelvic floor muscles (PFMs). Coughing can cause urinary leakage and is often used to test SUI. However, PFM characteristics during coughing, including their reliability, have not been investigated. Here, we used electromyography (EMG) to describe PFM pre-activity and reflexivity during coughing and examined the reliability of the measurements. METHODS This was an exploratory and reliability study including 11 young healthy women to characterize EMG reflex activity in PFMs during coughing. We describe 6 variables, averaged over 3 coughs per subject, and tested their reliability (intraclass correlation coefficient 3,1 [ICC(3,1)] and ICC(3,k), related standard error of measurement (SEM) and minimal difference [MD]). The variables represented the mean EMG activity for PFMs during 30-ms time intervals of pre-activity (initial time point of coughing [T0] and minus 30ms) and reflex activity (T0-30, 30-60, 60-90, 90-120 and 120-150ms after T0) of stretch-reflex latency responses. RESULTS The mean %EMG (normalized to maximal voluntary PFM contraction) for EMG variables was 35.1 to 52.2 and was significantly higher during coughing than for PFM activity at rest (mean 24.9±3.7%EMG; P<0.05). ICC(3,k) ranged from 0.67 to 0.91 (SEM 6.1-13.3%EMG and MD 16.7-36.8%EMG) and was higher than ICC(3,1) (range 0.40-0.77; SEM 9.0-18.0%EMG, MD 24.9-50.0%EMG). CONCLUSIONS PFM activity during reflex latency response time intervals during coughing was significantly higher than at rest, which suggests PFM pre-activity and reflex activity during coughing. Although we standardized coughing, EMG variables for PFM activity showed poor reliability [good to excellent ICC(3,k) and fair to excellent ICC(3,1) but high SEM and MD]. Therefore, coughing is expected to be heterogeneous, with low reliability, in clinical test situations. Potential crosstalk from other muscles involved in coughing could limit the interpretation of our results.

Evaluation of pelvic floor muscle activity during running in continent and incontinent women: An exploratory study.

Impact activities like running are known to elicit symptoms of stress urinary incontinence (SUI). The aim of this study was to investigate and compare pelvic floor muscle activity in continent and SUI women during running at three different speeds and thereby elucidate contraction characteristics of the pelvic floor during impact.

Neuromuscular Control Mechanisms During Single-Leg Jump Landing in Subacute Ankle Sprain Patients: A Case Control Study

Optimal neuromuscular control mechanisms are essential for preparing, maintaining, and restoring functional joint stability during jump landing and to prevent ankle injuries. In subacute ankle sprain patients, neither muscle activity nor kinematics during jump landing has previously been assessed.

Evaluation of pelvic floor kinematics in continent and incontinent women during running: An exploratory study

Impact activity like running is associated with an increase in intra‐abdominal pressure which needs to be sufficiently countered by pelvic floor muscle (PFM) activity to secure continence. The aim of this study was to investigate and compare PFM kinematics in continent and incontinent women during running.

Acute effects of partial-body vibration in sitting position

AIM To investigate the acute effects of sinusoidal and stochastic resonance partial-body vibration in sitting position, including muscle activity, heart rate variability, balance and flexibility. METHODS Fifty healthy participants were assigned randomly to two training conditions: A sinusoidal partial-body vibration (SIN, 8 Hz) or a stochastic resonance partial-body vibration (STOCH, 8 ± 2 Hz). For baseline assessment participants sat on the vibration platform without vibration. Both training conditions consisted of five series of a one-minute vibration training and a one-minute break between them. In this experimental study surface electromyography (EMG) of the erector spinae (ES), one of the back muscles, and heart rate variability (HRV) was measured at baseline and during training. Balance and flexibility were assessed at baseline and immediately after training. Balance was measured with the modified star excursion balance test (mSEBT) and flexibility was assessed through the modified fingertip-to-floor method (mFTF). RESULTS Paired sample t-test showed a significant increase in balance that was restricted to STOCH (t = -2.22, P = 0.018; SIN: t = -0.09, P = 0.466). An increase in flexibility was also restricted to STOCH (t = 2.65, P = 0.007; SIN: t = 1.41, P = 0.086). There was no significant change of muscle activity in the ES-EMG in STOCH or SIN conditions. In both training conditions, HRV decreased significantly, but remained in a low-load range (STOCH: t = 2.89, P = 0.004; SIN: t = 2.55, P = 0.009). CONCLUSION In sitting position, stochastic resonance partial-body vibration can improve balance and flexibility while cardiovascular load is low. STOCH can be a valuable training option to people who are unable to stand (e.g., people, who are temporarily wheelchair-bound).

The influence of gait and speed on the dynamic navicular drop – A cross sectional study on healthy subjects

INTRODUCTION Variations of gait speed influence kinematic variables that may have an effect on dynamic foot deformation. The influence of gait speed on the navicular drop has not yet been investigated. METHODS The navicular drop was evaluated in static and dynamic conditions using a 3D-motion capture system. The dynamic navicular drop was evaluated on a treadmill while walking and running at three different speeds. A repeated measures ANOVA and post-hoc tests were conducted to evaluate the differences in dynamic navicular drop, corresponding unloaded navicular height at foot strike and loaded navicular height during stance. RESULTS Higher walking speed led to a significant decrease in navicular height at foot strike and a subsequent decrease of dynamic navicular drop (p=0.006). Across increasing running speeds, minimum navicular height was significantly decreased which in consequence led to an increased dynamic navicular drop (p=0.015). For walking and running at the same speed, there was a large effect of gait style with an increase of dynamic navicular drop by 3.5mm (p<0.001) during running. DISCUSSION The change of gait from walking to running at the same speed had a large effect on dynamic navicular drop. The values of navicular height at foot strike and minimum navicular height during stance should be taken into account for the interpretation of dynamic navicular drop measures. Static and dynamic navicular drop measures differ substantially.

Intra- and interday reliability of the dynamic navicular rise, a new measure for dynamic foot function: A descriptive, cross-sectional laboratory study

BACKGROUND The lack of reliable parameters to evaluate dynamic foot function, emphasizes the need for a deeper insight in foot biomechanics. The aims were to investigate the reliability of a new parameter (dynamic navicular rise dNR), and its relationship with the dynamic navicular drop (dND). METHODS Twenty healthy participants (mean age 30.2±8.1years) had to walk on even ground and downstairs. Data of ten trials per task on two measurement days were recorded. The dNR was defined as the difference in millimetres (mm) between the minimum navicular height (NH) during stance and the NH at toe off. To test intra- and interday reliability, Intraclass Correlation Coefficients (ICC2.1) and repeatability were calculated. To obtain the absolute repeatability (RP) in mm, the equation RP=1.96×SDdifferences was used. Furthermore, the relationship between the dNR and the dND was examined by calculating Pearson (r) or Spearman (rs) correlation coefficients. RESULTS Included participants showed a mean dNR of (12.2±3.7) mm for level walking and (14.8±3.4) mm for stair descent. The ICC2.1 for the dNR were 0.98 (intraday), 0.91 (interday) for level walking and 0.97 (intraday), 0.94 (interday) for stair descent. The interday repeatability was 3.2mm (level walking), 2.7mm (stair descent) respectively. For level walking, r was 0.31 (p=0.049), and rs=0.88 (p<0.001) for stair descent. CONCLUSIONS The dNR seems to be highly reliable (ICCs), however, repeatability is unacceptable. For level walking, the dNR might be an independent measure, but not for stair climbing.

A minimal markerset for three-dimensional foot function assessment: measuring navicular drop and drift under dynamic conditions

BackgroundThe validity of predicting foot pronation occurring mainly at the midfoot by surrogate measures from the rearfoot, like eversion excursion, is limited. The dynamic navicular mobility in terms of vertical navicular drop (dNDrop) and medial navicular drift (dNDrift) may be regarded as meaningful clinical indicators to represent overall foot function. This study aimed to develop a minimal approach to measure the two parameters and to examine their intra- and interday reliability during walking.MethodsThe minimal markerset uses markers at the lateral and medial caput of the 1st and 5th metatarsals, respectively, at the dorsal calcaneus and at the tuberosity of the navicular bone. Dynamic navicular drop and drift were assessed with three-dimensional motion capture in 21 healthy individuals using a single-examiner test-retest study design.ResultsIntra- and interday repeatability were 1.1 mm (ICC21 0.97) and 2.3 mm (ICC21 0.87) for dynamic navicular drop and 1.5 mm (ICC21 0.96) and 5.3 mm (ICC21 0.46) for dynamic navicular drift. The contribution of instrumental errors was estimated to 0.25 mm for dynamic navicular drop and 0.86 mm for dynamic navicular drift.ConclusionsInterday reliability was generally worse than intraday reliability primary due to day-to-day variations in movement patterns and the contribution of instrumental errors was below 23% for dynamic navicular drop but reached 57% for dynamic navicular drift. The minimal markerset allows to simply transfer the known concepts of navicular drop and drift from quasi-static clinical test conditions to functional tasks, which is recommended to more closely relate assessments to the functional behavior of the foot.

Walking with an induced unilateral knee extension restriction affects lower but not upper body biomechanics in healthy adults

BACKGROUND Unilateral knee flexion contractures (KFC) are frequently seen in orthopedic rehabilitation and often interfere with the normal gait pattern, resulting in passive and/or active secondary deviations. In order to prevent KFC-related complications such as patellofemoral pain or the knee spine syndrome, a comprehensive understanding of such deviations is necessary. RESEARCH QUESTION How does an artificially induced unilateral KFC affect whole body biomechanics in young healthy adults during gait? METHODS Twenty-four healthy young adults (females/males: 13/11; mean age: 27.3 ± 3.8 years) were included in this cross-sectional study. Using an 8-camera optical motion capture system and two embedded force plates, three-dimensional lower extremity, pelvis and trunk kinematics as well as lower extremity joint moments were derived during normal walking and walking with unilateral KFCs by means of a lightweight knee brace locked at 30° and 60° of flexion. Data were analyzed using one-dimensional statistical parametric mapping, allowing explorative group comparisons of continuous data rather than pre-defined discrete parameters. RESULTS On the braced side, increased hip flexion (p < 0.001, 1-100 % of gait cycle [%GC]), knee flexion (p < 0.001, 1-72 and 82-100 %GC) and ankle dorsiflexion angles (p < 0.001, 1-100 %GC) as well as external knee flexion moments (p < 0.001, 1-98 % of stance phase [%StPh]) and decreased ankle dorsiflexion (p < 0.001, 74-94 %StPh), hip flexion and hip adduction moments (p < 0.001, 1-32 %StPh and p < 0.001, 71-92 %StPh, respectively) were observed. The unbraced side showed similar but less pronounced deviations. Pelvis and upper body kinematics were not altered, suggesting that the lower limbs fully compensate for KFCs of less than 30°. SIGNIFICANCE Asymmetric limb loading and considerable increases in external knee flexion moments might increase the risk for adverse effects of lower extremity joints in the long-term. It seems therefore important to treat KFCs as early as possible and to implement preventive strategies to avoid possible complications.BACKGROUND Unilateral knee flexion contractures (KFC) are frequently seen in orthopedic rehabilitation and often interfere with the normal gait pattern, resulting in passive and/or active secondary deviations. In order to prevent KFC-related complications such as patellofemoral pain or the knee spine syndrome, a comprehensive understanding of such deviations is necessary. RESEARCH QUESTION How does an artificially induced unilateral KFC affect whole body biomechanics in young healthy adults during gait? METHODS Twenty-four healthy young adults (females/males: 13/11; mean age: 27.3 ± 3.8 years) were included in this cross-sectional study. Using an 8-camera optical motion capture system and two embedded force plates, three-dimensional lower extremity, pelvis and trunk kinematics as well as lower extremity joint moments were derived during normal walking and walking with unilateral KFCs by means of a lightweight knee brace locked at 30° and 60° of flexion. Data were analyzed using one-dimensional statistical parametric mapping, allowing explorative group comparisons of continuous data rather than pre-defined discrete parameters. RESULTS On the braced side, increased hip flexion (p < 0.001, 1-100 % of gait cycle [%GC]), knee flexion (p < 0.001, 1-72 and 82-100 %GC) and ankle dorsiflexion angles (p < 0.001, 1-100 %GC) as well as external knee flexion moments (p < 0.001, 1-98 % of stance phase [%StPh]) and decreased ankle dorsiflexion (p < 0.001, 74-94 %StPh), hip flexion and hip adduction moments (p < 0.001, 1-32 %StPh and p < 0.001, 71-92 %StPh, respectively) were observed. The unbraced side showed similar but less pronounced deviations. Pelvis and upper body kinematics were not altered, suggesting that the lower limbs fully compensate for KFCs of less than 30°. SIGNIFICANCE Asymmetric limb loading and considerable increases in external knee flexion moments might increase the risk for adverse effects of lower extremity joints in the long-term. It seems therefore important to treat KFCs as early as possible and to implement preventive strategies to avoid possible complications.