Fredrik Öhberg

Chronic whiplash associated disorders and neck movement measurements: an instantaneous helical axis approach

This paper presents an assessment tool for objective neck movement analysis of subjects suffering from chronic whiplash-associated disorders (WAD). Three-dimensional (3-D) motion data is collected by a commercially available motion analysis system. Head rotation, defined in this paper as the rotation angle around the instantaneous helical axis (IHA), is used for extracting a number of variables (e.g., angular velocity and range, symmetry of motion). Statistically significant differences were found between controls and subjects with chronic WAD in a number of variables.

Ensemble coding of muscle stretches in afferent populations containing different types of muscle afferents.

Ensemble coding of simple mechanical stimuli (small sinusoidal stretches) was studied in simultaneously recorded mixed ensembles of primary- and secondary muscle spindle afferents (MSAs), and Golgi tendon organ (GTO) afferents recorded from L7-S1 dorsal root filaments. The experiments were made on 48 recorded afferents (29 primary MSAs, 6 secondary MSAs and 13 GTO afferents) in chloralose anaesthetised cats. For the analyses, we used a combination of principal component analysis and algorithms for quantification of stimulus discrimination. Mixed ensembles of primary- and secondary MSAs, and GTO afferents, discriminated significantly better between different muscle stretches than ensembles of only one or two types of these afferents. All kinds of ensembles showed a successive increase in discriminative ability with increased ensemble size and this ability seemed to level at larger populations. However, the increase in discriminative ability was significantly greater for the mixed ensembles. It is hypothesised that the main reason for the greater discriminative ability achieved by mixed ensembles, might be that the variation in response profiles (sensitivity tuning) among the individual afferents of the mixed ensemble will be larger than that for ensembles of only one type of afferent. Finally, the results in the present study give experimental support to some of the teleological arguments in favour of the ensemble coding theory.

Quadriceps EMG in Open and Closed Kinetic Chain Tasks in Women With Patellofemoral Pain

The authors investigated whether the discrepancy noted in the literature regarding delayed and decreased activity in vastus medialis obliquus (VMO) in people with patellofemoral pain (PFP) depends on the nature of the open kinetic chain (OKC) and the closed kinetic chain (CKC) in the experimental task. They hypothesized that activity in VMO would be more delayed and decreased in CKC tasks than in OKC tasks. Women with PFP (n = 17) and healthy controls (n = 17) performed isometric quadriceps contractions in CKC and OKC tasks. The authors manipulated only the application of resistance. Electromyographs (EMGs) showed that participants with PFP reacted later and activated the quadriceps more in the CKC task but had intramuscular quadriceps coordination similar to that of controls. The nature of the OKC task or the CKC task does not seem to explain contradictory findings regarding VMO activation.

Classification of neck movement patterns related to whiplash-associated disorders using neural networks

This paper presents a new method for classification of neck movement patterns related to whiplash-associated disorders (WAD) using a resilient backpropagation neural network (BPNN). WAD are a common diagnosis after neck trauma, typically caused by rear-end car accidents. Since physical injuries seldom are found with present imaging techniques, the diagnosis can be difficult to make. The active range of the neck is often visually inspected in patients with neck pain, but this is a subjective measure, and a more objective decision support system, that gives a reliable and more detailed analysis of neck movement pattern, is needed. The objective of this study was to evaluate the predictive ability of a BPNN, using neck movement variables as input. Three-dimensional (3-D) neck movement data from 59 subjects with WAD and 56 control subjects were collected with a ProReflex system. Rotation angle and angle velocity were calculated using the instantaneous helical axis method and motion variables were extracted. A principal component analysis was performed in order to reduce data and improve the BPNN performance. BPNNs with six hidden nodes had a predictivity of 0.89, a sensitivity of 0.90 and a specificity of 0.88, which are very promising results. This shows that neck movement analysis combined with a neural network could build the basis of a decision support system for classifying suspected WAD, even though further evaluation of the method is needed.

Three-Dimensional Camera System for Measuring Arm Volume in Women with Lymphedema Following Breast Cancer Treatment

BACKGROUND Lymphedema is a common complication following breast cancer treatment, estimated to affect 20% of breast cancer survivors. The condition is associated with a number of symptoms, such as impaired range of motion and anxiety. A wide range of methods for determining the volume of the lymphedematous arm have been described. Circumference measurement (CM) is commonly used in clinics to appraise arm volume, while water displacement (WD) is often used in studies. The aim of the study was to assess the performance of a new method using 3D-technology in comparison to CM and WD. METHODS AND RESULTS The study was performed on 25 subjects with lymphedema secondary to breast cancer treatment. Volumetric data from CM, WD, and the 3D-camera were gathered on all subjects. The measurements were performed by two physiotherapists, each subject being measured by one of the physiotherapist. Estimates of differences between the methods was calculated through analyzing the data collected from the three methods using mixed-design analyses of variance. The results indicated a tendency for the 3D-camera to overestimate the volume in comparison the WD by 45.25 mL, 95% confidence interval (CI) -36.31 - 126.82 (p value 0.270). Conversely, CM showed a tendency to underestimate the volume compared to WD (-24.28 mL, CI -99.78 - 51.22, p value 0.521). Thus, no statistically significant difference was found between the methods. CONCLUSIONS The 3D-camera is a viable method for measuring arm volume, performing on level with the established methods WD and CM.

Compensatory strategies for muscle weakness during stair ascent in subjects with total knee arthroplasty

Subjects with total knee arthroplasty (TKA) exhibit decreased quadriceps and hamstring strength. This may bring about greater relative effort or compensatory strategies to reduce knee joint moments in daily activities. To study gait and map out the resource capacity, knee muscle strength was assessed by maximal voluntary concentric contractions, and whole body kinematics and root mean square (RMS) electromyography (EMG) of vastus lateralis and semitendinosus were recorded during stair ascent in 23 unilateral TKA-subjects ~19 months post-operation, and in 23 healthy controls. Muscle strength and gait velocity were lower in the TKA group, but no significant group differences were found in RMS EMG or forward trunk lean. The results suggest that reduced walking velocity sufficiently compensated for reduced knee muscle strength.

Comparative analysis of different adaptive filters for tracking lower segments of a human body using inertial motion sensors

For all segments and tests, a modified Kalman filter and a quasi-static sensor fusion algorithm were equally accurate (precision and accuracy ∼2‐3 ◦ ) compared to normalized least mean squares filtering, recursive least-squares filtering and standard Kalman filtering. The aims were to: (1) compare adaptive filtering techniques used for sensor fusion and (2) evaluate the precision and accuracy for a chosen adaptive filter. Motion sensors (based on inertial measurement units) are limited by accumulative integration errors arising from sensor bias. This drift can partly be handled with adaptive filtering techniques. To advance the measurement technique in this area, a new modified Kalman filter is developed. Differences in accuracy were observed during different tests especially drift in the internal/external rotation angle. This drift can be minimized if the sensors include magnetometers.

AGNES: Connecting people in a multimodal way

Western societies are confronted with a number of challenges caused by the increasing number of older citizens. One important aspect is the need and wish of older people to live as long as possible in their own home and maintain an independent life. As people grew older, their social networks disperse, with friends and families moving to other parts of town, other cities or even countries. Additionally, people become less mobile with age, leading to less active participation in societal life. Combined, this normal, age-related development leads to increased loneliness and social isolation of older people, with negative effects on mental and physical health of those people. In the AGNES project, a home-based system has been developed that allows connecting elderly with their families, friends and other significant people over the Internet. As most older people have limited experience with computers and often special requirements on technology, one focus of AGNES was to develop with the users novel technological means for interacting with their social network. The resulting system uses ambient displays, tangible interfaces and wearable devices providing ubiquitous options for interaction with the network, and secondary sensors for additionally generating carefully chosen information on the person to be relayed to significant persons. Evaluations show that the chosen modalities for interaction are well adopted by the users. Further it was found that use of the AGNES system had positive effects on the mental state of the users, compared to the control group without the technology.

Individual Differences in Motor Timing and Its Relation to Cognitive and Fine Motor Skills

The present study investigated the relationship between individual differences in timing movements at the level of milliseconds and performance on selected cognitive and fine motor skills. For this purpose, young adult participants (N = 100) performed a repetitive movement task paced by an auditory metronome at different rates. Psychometric measures included the digit-span and symbol search subtasks from the Wechsler battery as well as the Raven SPM. Fine motor skills were assessed with the Purdue Pegboard test. Motor timing performance was significantly related (mean r = .3) to cognitive measures, and explained both unique and shared variance with information-processing speed of Ravens scores. No significant relations were found between motor timing measures and fine motor skills. These results show that individual differences in cognitive and motor timing performance is to some extent dependent upon shared processing not associated with individual differences in manual dexterity.

Peak knee flexion angles during stair descent in TKA patients

Reduced peak knee flexion during stair descent (PKSD) is demonstrated in subjects with total knee arthroplasty (TKA), but the underlying factors are not well studied. 3D gait patterns during stair descent, peak passive knee flexion (PPKF), quadriceps strength, pain, proprioception, demographics, and anthropometrics were assessed in 23 unilateral TKA-subjects ~19 months post-operatively, and in 23 controls. PKSD, PPKF and quadriceps strength were reduced in the TKA-side, but also in the contralateral side. A multiple regression analysis identified PPKF as the only predictor (57%) to explain the relationship with PKSD. PPKF was, however sufficient for normal PKSD. Deficits in quadriceps strength in TKA-group suggest that strength is also contributing to smaller PKSD. Increased hip adduction at PKSD may indicate both compensatory strategy and reduced hip strength.