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  • 1.
    Ekblom, Maria
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Ovendal, Alexander
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Tais, Senna
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Halvorsen, Kjartan
    KTH.
    Eriksson, Martin
    KTH.
    Acute effects of concurrent EMG feedback on knee extensor strength and activation2012Conference paper (Refereed)
  • 2. Forsell, Caroline
    et al.
    Halvorsen, Kjartan
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    A method for determining minimal sets of markers for the estimation of center of mass, linear and angular momentum.2009In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 42, no 3, p. 361-5Article in journal (Refereed)
    Abstract [en]

    A new method is proposed for finding small sets of points on the body giving sufficient information for estimating the whole body center of mass (CoM), as well as the linear momenta (LM) and angular momenta (AM). In the underlying model each point (whose trajectory is tracked by a marker) is a point mass: Hence the body is represented by a simple system of point masses. The first step is to determine the appropriate set of points and the mass of each point, which is assumed to be specific for the movement performed. The distribution of the mass to each marker is determined from training data for which the true (or reference) trajectories of the CoM, LM or AM are known. This leads to a quadratic optimization problem with inequality constraints. The use of the method is demonstrated on data from discus throw. Results indicate reasonably small errors, considering the magnitude of other error sources, in CoM position (average magnitude of estimation error 1-2cm), and moderate errors in AM (13-20% of peak value).

  • 3. Frohm, A
    et al.
    Halvorsen, Kjartan
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Thorstensson, Alf
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Patellar tendon load in different types of eccentric squats.2007In: Clinical Biomechanics, ISSN 0268-0033, E-ISSN 1879-1271, Vol. 22, no 6, p. 704-11Article in journal (Refereed)
    Abstract [en]

    BACKGROUND: Differences in mechanical loading of the patellar tendon have been suggested as a reason for varying effects in rehabilitation of patellar tendinopathy using different eccentric squat exercises and devices. The aim was to characterize the magnitude and pattern of mechanical load at the knee and on the patellar tendon during four types of eccentric squat. METHODS: Subjects performed squats with a submaximal free weight and with maximal effort in a device for eccentric overloading (Bromsman), on a decline board and horizontal surface. Kinematics was recorded with a motion-capture system, reaction forces with force plates, and electromyography from three leg muscles with surface electrodes. Inverse dynamics was used to calculate knee joint kinetics. FINDINGS: Eccentric work, mean and peak patellar tendon force, and angle at peak force were greater (25-30%) for squats on decline board compared to horizontal surface with free weight, but not in Bromsman. Higher knee load forces (60-80%), but not work, were observed with Bromsman than free weight. Angular excursions at the knee and ankle were larger with decline board, particularly with free weight, and smaller in Bromsman than with free weight. Mean electromyography was greater on a decline board for gastrocnemius (13%) and vastus medialis (6%) with free weight, but in Bromsman only for gastrocnemius (7%). INTERPRETATION: The results demonstrated clear differences in the biomechanical loading on the knee during different squat exercises. Quantification of such differences provides information that could be used to explain differences in rehabilitation effects as well as in designing more optimal rehabilitation exercises for patellar tendinopathy.

  • 4. Frohm, Anna
    et al.
    Halvorsen, Kjartan
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Thorstensson, Alf
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    A new device for controlled eccentric overloading in training and rehabilitation.2005In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 94, no 1-2, p. 168-74Article in journal (Refereed)
    Abstract [en]

    The aim of this work was to evaluate a device that allows for eccentric overload to be applied under controlled and safe conditions and it is applicable in exercises commonly used in training and rehabilitation. The machine contains a barbell, which is lowered and raised by a motor, following a predetermined velocity profile. It is capable of handling heavy loads (>500 kg) and is instrumented with a sensor to measure the velocity of the barbell and two scales to measure the vertical component of the ground reaction force. The velocity recordings of the built-in displacement sensor were found to correspond well with those obtained using a motion-capture system. Applying known weights on each scale demonstrated linearity with respect to magnitude and independence regarding location of application. The velocity of the barbell was found to be dependent on the load on the barbell and on the resisting force produced by the individual training in the machine. The combined man-machine reliability was tested using a group of habitually active males (n = 13, 28-55 years) performing squats. Peak voluntary resisting force and position at peak resistance were recorded on two occasions, showing no significant differences and a coefficient of variation of 9% and 22%, respectively. Preliminary observations from training in the machine have been positive both for increasing performance in top athletes and for causing pain relief in patients with diffuse knee problems. The possibility of feedback of the force under each foot makes individual dosage of training load possible, which is valuable, e.g. in rehabilitation of a unilateral injury.

  • 5. Frohm, Anna
    et al.
    Saartok, Tönu
    Halvorsen, Kjartan
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Renström, Per
    Eccentric treatment for patellar tendinopathy: a prospective randomised short-term pilot study of two rehabilitation protocols.2007In: British Journal of Sports Medicine, ISSN 0306-3674, E-ISSN 1473-0480, Vol. 41, no 7, p. e7-Article in journal (Refereed)
    Abstract [en]

    OBJECTIVE: To compare the efficacy and safety of two eccentric rehabilitation protocols for patients with symptomatic patellar tendinopathy. A new eccentric overload training device was compared with the present standard eccentric rehabilitation programme on a decline board. DESIGN: Prospective, randomised clinical trial. SETTING: Sports rehabilitation clinic, university sports laboratory, supplemented with home exercises. PATIENTS: 20 competitive and recreational athletes, all with clinical diagnosis of patellar tendinopathy, verified by MRI or ultrasound imaging. INTERVENTIONS: A 12-week rehabilitation period, either with bilateral eccentric overload strength training using the Bromsman device twice a week or with unilateral eccentric body load training using a decline board twice a week, supplemented with daily home exercises. OUTCOME MEASURES: The primary outcome was pain and function, assessed by the Swedish Victorian Institute of Sport Assessment for Patella (VISA-P) score. Secondary outcome measures were isokinetic muscle torque, dynamic function and muscle flexibility, as well as pain level estimations using visual analogue scale (VAS). Side effects were registered. RESULTS: Both treatment groups improved in the short term according to the VISA-P scores during the 12-week rehabilitation period. However, there were no significant differences between the groups in terms of pain and function. After a 3-month rehabilitation period, most patients could be regarded as improved enough to be able to return to training and sports. No serious side effects were detected in either group. CONCLUSION: In patients with patellar tendinopathy pain, two-legged eccentric overload training twice per week, using the new device (Bromsman), was as efficient and safe as the present standard daily eccentric one-legged rehabilitation-training regimen using a decline board.

  • 6. Frykberg, Gunilla E
    et al.
    Åberg, Anna Cristina
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences.
    Halvorsen, Kjartan
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Borg, Jörgen
    Hirschfeld, Helga
    Temporal coordination of the sit-to-walk task in subjects with stroke and in controls.2009In: Archives of physical medicine and rehabilitation, ISSN 1532-821X, Vol. 90, no 6, p. 1009-17Article in journal (Refereed)
    Abstract [en]

    OBJECTIVES: To explore events and describe phases for temporal coordination of the sit-to-walk (STW) task, within a semistandardized set up, in subjects with stroke and matched controls. In addition, to assess variability of STW phase duration and to compare the relative duration of STW phases between the 2 groups. DESIGN: Cross-sectional. SETTING: Research laboratory. PARTICIPANTS: A convenience sample of persons with hemiparesis (n=10; age 50-67y) more than 6 months after stroke and 10 controls matched for sex, age, height, and body mass index. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Relative duration of STW phases, SE of measurement in percentage of the mean, and intraclass correlation coefficients (ICCs). RESULTS: Four STW phases were defined: rise preparation, transition, primary gait initiation, and secondary gait initiation. The subjects with stroke needed 54% more time to complete the STW task than the controls did. ICCs ranged from .38 to .66 and .22 to .57 in the stroke and control groups, respectively. SEs of measurement in percentage of the mean values were high, particularly in the transition phase: 54.1% (stroke) and 50.4% (controls). The generalized linear model demonstrated that the relative duration of the transition phase was significantly longer in the stroke group. CONCLUSIONS: The present results extend existing knowledge by presenting 4 new phases of temporal coordination of STW, within a semistandardized set-up, in persons with stroke and in controls. The high degree of variability regarding relative STW phase duration was probably a result of both the semistandardized set up and biological variability. The significant difference in the transition phase across the 2 groups requires further study.

  • 7. Frykberg, Gunilla
    et al.
    Åberg, Anna Cristina
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences.
    Halvorsen, Kjartan
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Hirschfeld, Helga
    Temporal characteristics of the sit-to-walk task in subjects with stroke and in controls - Preliminary results2007In: The 16th annual meeting of ESMAC. September 2007, Athens Greece, 2007Conference paper (Other academic)
  • 8. Gullstrand, Lennart
    et al.
    Halvorsen, Kjartan
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Tinmark, Fredrik
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Eriksson, Martin
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Nilsson, Johnny
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Measurements of vertical displacement in running, a methodological comparison.2009In: Gait & posture, ISSN 1879-2219, Vol. 30, no 1, p. 71-75Article in journal (Refereed)
    Abstract [en]

    The aim was (1) to evaluate measurements of vertical displacements (V(disp)) of a single point on sacrum as an estimate of the whole body centre of mass (CoM) V(disp) during treadmill running and (2) to compare three methods for measuring this single point. These methods were based on a position transducer (PT), accelerometers (AMs) and an optoelectronic motion capture system. Criterion method was V(disp) of the whole body CoM measured with the motion capture system. Thirteen subjects ran at 10, 12, 14, 16, 18, 20 and 22kmh(-1) with synchronous recordings with the three methods. Four measurements of the (V(disp)) were derived: (1) V(disp) of CoM calculated from a segment model consisting of 13 segments tracked with 36 reflective markers, (2) V(disp) of the sacrum recorded with the PT, (3) V(disp) of the sacrum calculated from the AM, and (4) V(disp) of the sacrum calculated as the mid point of two reflective markers (sacrum marker, SM) attached at the level of the sacral bone. The systematic discrepancy between the measurements of sacrum V(disp) and CoM V(disp) varied between 0 and 1.5mm and decreased with increasing running velocity and decreasing step duration. PT and SM measurements showed strong correlation, whereas the AM showed a variability increasing with velocity. The random discrepancy within each subject was 7mm for all three methods. In conclusion single-point recordings of the sacrum V(disp) may be used to monitor changes in V(disp) of CoM during treadmill running.

  • 9.
    Halvorsen, Kjartan
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Eriksson, Martin
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Gullstrand, Lennart
    Tinmark, Fredrik
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Nilsson, Johnny
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Minimal marker set for center of mass estimation in running.2009In: Gait & Posture, ISSN 0966-6362, E-ISSN 1879-2219, Vol. 30, no 4, p. 552-555Article in journal (Refereed)
    Abstract [en]

    The purpose was to study the validity of a recently proposed method [Forsell C, Halvorsen K. A method for determining minimal sets of markers for the estimation of center of mass, linear and angular momentum. Journal of Biomechanics 2009;42(3):361-5] for estimating the trajectory of the whole-body center of mass (CoM) in the case of running at velocities ranging from 10 to 22 kmh(-1). The method gives an approximation to the CoM using the position of fewer markers on the body than the standard method of tracking each segment of the body. Fourteen male athletes participated. A standard method for determining the CoM from a model of 13 segments and using the position of 36 markers was used as reference method. Leave-one-out cross-validation revealed errors that decreased with increasing number of markers used in the approximative method. Starting from four markers, the error in absolute position of the CoM decreased from 15mm to 3mm in each direction. For the velocity of the CoM the estimation bias was neglectable, and the random error decreased from 0.15 to 0.05 ms(-1). The inter-subject and intra-subject variability in the estimated model parameters increased with increasing number of markers. The method worked well also when applied to running at velocities outside the range of velocities in the data used to determine the model parameters. The results indicate that a model using 10 markers represents a good trade-off between simplicity and accuracy, but users must take into account requirements of their specific applications.

  • 10.
    Halvorsen, Kjartan
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Johnston, Christopher
    Back, Willem
    Stokes, Virgil
    Lanshammar, Håkan
    Tracking the motion of hidden segments using kinematic constraints and Kalman filtering.2008In: Journal of Biomechanical Engineering, ISSN 0148-0731, E-ISSN 1528-8951, Vol. 130, no 1, p. 011012-Article in journal (Refereed)
    Abstract [en]

    Motion capture for biomechanical applications involves in almost all cases sensors or markers that are applied to the skin of the body segments of interest. This paper deals with the problem of estimating the movement of connected skeletal segments from 3D position data of markers attached to the skin. The use of kinematic constraints has been shown previously to reduce the error in estimated segment movement that are due to skin and muscles moving with respect to the underlying segment. A kinematic constraint reduces the number of degrees of freedom between two articulating segments. Moreover, kinematic constraints can help reveal the movement of some segments when the 3D marker data otherwise are insufficient. Important cases include the human ankle complex and the phalangeal segments of the horse, where the movement of small segments is almost completely hidden from external observation by joint capsules and ligaments. This paper discusses the use of an extended Kalman filter for tracking a system of connected segments. The system is modeled using rigid segments connected by simplified joint models. The position and orientation of the mechanism are specified by a set of generalized coordinates corresponding to the mechanism's degrees of motion. The generalized coordinates together with their first time derivatives can be used as the state vector of a state space model governing the kinematics of the mechanism. The data collected are marker trajectories from skin-mounted markers, and the state vector is related to the position of the markers through a nonlinear function. The Jacobian of this function is derived. The practical use of the method is demonstrated on a model of the distal part of the limb of the horse. Monte Carlo simulations of marker data for a two-segment system connected by a joint with three degrees of freedom indicate that the proposed method gives significant improvement over a method, which does not make use of the joint constraint, but the method requires that the model is a good approximation of the true mechanism. Applying the method to data on the movement of the four distal-most segments of the horse's limb shows good between trial consistency and small differences between measured marker positions and marker positions predicted by the model.

  • 11.
    Halvorsen, Kjartan
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Söderström, Torsten
    Stokes, Virgil
    Lanshammar, Håkan
    Using an extended kalman filter for rigid body pose estimation.2005In: Journal of Biomechanical Engineering, ISSN 0148-0731, E-ISSN 1528-8951, Vol. 127, no 3, p. 475-83Article in journal (Refereed)
    Abstract [en]

    Rigid body pose is commonly represented as the rigid body transformation from one (often reference) pose to another This is usually computed for each frame of data without any assumptions or restrictions on the temporal change of the pose. The most common algorithm was proposed by Söderkvist and Wedin (1993, "Determining the Movements of the Skeleton Using Well-configured Markers," J. Biomech., 26, pp. 1473-1477), and implies the assumption that measurement errors are isotropic and homogenous. This paper describes an alternative method based on a state space formulation and the application of an extended Kalman filter (EKF). State space models are formulated, which describe the kinematics of the rigid body. The state vector consists of six generalized coordinates (corresponding to the 6 degrees of freedom), and their first time derivatives. The state space models have linear dynamics, while the measurement function is a non-linear relation between the state vector and the observations (marker positions). An analytical expression for the linearized measurement function is derived. Tracking the rigid body motion using an EKF enables the use of a priori information on the measurement noise and type of motion to tune the filter. The EKF is time variant, which allows for a natural way of handling temporarily missing marker data. State updates are based on all the information available at each time step, even when data from fewer than three markers are available. Comparison with the method of Söderkvist and Wedin on simulated data showed a considerable improvement in accuracy with the proposed EKF method when marker data was temporarily missing. The proposed method offers an improvement in accuracy of rigid body pose estimation by incorporating knowledge of the characteristics of the movement and the measurement errors. Analytical expressions for the linearized system equations are provided, which eliminate the need for approximate discrete differentiation and which facilitate a fast implementation.

  • 12. Harringe, M L
    et al.
    Halvorsen, Kjartan
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Renström, Per
    Karolinska institutet.
    Werner, S
    Postural control measured as the center of pressure excursion in young female gymnasts with low back pain or lower extremity injury.2008In: Gait & Posture, ISSN 0966-6362, E-ISSN 1879-2219, Vol. 28, no 1, p. 38-45Article in journal (Refereed)
    Abstract [en]

    Gymnasts are known to practice and compete although suffering from injuries and pain. Pain may change strategies for postural control. The primary aim of the present study was to investigate how center of pressure (COP) measurements are influenced by low back pain and lower extremity injury in top-level female gymnasts. A secondary aim was to study the reliability of these measurements using a test-retest design, and how this depends on the duration of the test. Fifty-seven top-level gymnasts were included in four groups: non-injured (NI, n=18), low back pain (LBP, n=11), lower extremity injury (LEI, n=17) and a multiple injury group (MI, n=11). COP excursion during quiet stance was measured on a force platform, during 120s: (1) hard surface/eyes open, (2) hard surface/eyes closed, (3) foam surface/eyes open and (4) foam surface/eyes closed. The COP excursion increased, for all groups, during the foam surface/eyes closed measurement compared to the other three tests. Furthermore, the LBP group showed a 49% (p=0.01) larger COP area compared to the LEI group in the foam surface/eyes closed condition. Measurements on foam surface were in general more reliable than tests on hard surface and tests with eyes closed were more reliable than tests with eyes open. Tests during 120s were in most cases more reliable than tests during 60s. In conclusion the COP excursion is influenced by injury location. Quiet stance measurements on foam surface with eyes closed seems to be reliable and sensitive in young female gymnasts.

  • 13. Jönhagen, S
    et al.
    Halvorsen, Kjartan
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Benoit, D L
    Muscle activation and length changes during two lunge exercises: implications for rehabilitation.2009In: Scandinavian Journal of Medicine and Science in Sports, ISSN 0905-7188, E-ISSN 1600-0838, Vol. 19, no 4, p. 561-8Article in journal (Refereed)
    Abstract [en]

    Eccentric exercises are commonly used as a treatment for various muscle and tendon injuries. During complex motions such as the forward lunge, however, it is not always clear which muscles may be contracting eccentrically and at what time. Because this exercise is used during rehabilitation, the purpose of this investigation was to determine what type of contractions take place during two different types of forward lunge and assess the implications for rehabilitation. Five experienced athletes performed five cycles for each of the walking and jumping forward lunges. Motion analysis was used to calculate the shortening or elongation of each muscle based on the change of position of their origin and insertion points during the lunge. Electromyography of the lateral hamstrings, rectus femoris and lateral gastrocnemius was combined with the muscle length change data to determine when isometric, concentric and eccentric activations occur during the lunge. Eccentric contractions in both the quadriceps and gastrocnemius were observed during the lunge. No hamstring eccentric contractions were found; however, the hamstrings showed isometric contractions during the first part of the stance phase.

  • 14.
    Nilsson, Johnny
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Tinmark, Fredrik
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Halvorsen, Kjartan
    Arndt, Anton
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Kinematic, kinetic and electromyographic adaptation to speed and resistance in double poling cross country skiing2013In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 113, no 6, p. 1385-1394Article in journal (Refereed)
    Abstract [en]

    This study incorporated variations in speed and the horizontal resistance acting upon elite female skiers during double poling (DP) on a treadmill and specifically analyzed biomechanical adaptations to these variations. Whole body kinematics and pole force data were recorded and used to calculate the moment of force acting on the shoulder and elbow joints. Data were obtained with a 3D optoelectronic system using reflective markers at given anatomical landmarks. Forces along the long axis of the right pole were measured with a piezoelectric force transducer. Surface electrodes were used to record EMG activity in the rectus femoris, rectus abdominis, latissimus dorsi and triceps brachii muscles. In a first set of recordings, the participants double poled with zero elevation at five different speeds from 8 to 17 km h−1. In a second set of recordings, horizontal resistance was added by weights (0.4–1.9 kg) attached to a pulley system pulling the skier posteriorly during DP at 14 km h−1. Results showed increasing relative duration of the thrust phase with increasing resistance, but not with speed. Significant kinematic differences occurred with increase in both speed and resistance. The mean (±SD) horizontal force components ranged between 1.7 (±1.3) and 2.8 (±1.1) percent (%) bodyweight (BW) in the speed adaptation and 3.1 (±0.6) and 4.0 (±1.3) % BW in the adaptation to horizontal resistance. Peak muscle activity showed a central to peripheral (proximo-distal) activation sequence. The temporal cycle phase pattern in the adaptation to speed and horizontal resistance differed.

  • 15.
    Tais, Senna
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Eriksson, Martin
    KTH.
    Halvorsen, Kjartan
    KTH och Uppsala Universitet.
    Ekblom, Maria
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Effects of training with concurrent EMG feedback on Quadriceps stength and activation2012Conference paper (Refereed)
  • 16.
    Tarassova, Olga
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Halvorsen, Kjartan
    Åberg, Anna Christina
    Uppsala Universitet.
    Ekblom, Maria
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Balance mechanisms in children with and without motor coordination difficulties2012In: Balance mechanisms in children with and without motor coordination difficulties, 2012Conference paper (Refereed)
  • 17.
    Tinmark, Fredrik
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Hellström, John
    Arndt, Anton
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Halvorsen, Kjartan
    Contributions to club velocity in golf swings to submaximal and maximal shot distances2012In: eProceedings of the 30th Conference of the International Society of Biomechanics in Sports, 2012: Volume 3 / [ed] Bradshaw, E.J., Burnett, A., Hume, P.A., 2012, p. 81-83Conference paper (Refereed)
    Abstract [en]

    The contribution of joint rotations to endpoint velocity was investigated in golf shots to submaximal and maximal shot distances using a 41degrees of freedom (DOF) kinematic model. A subset of 16 DOFs was found to explain 97%-99% of endpoint velocity regulation at club–ball contact. The largest contributors, for both groups at every shot condition, were pelvis and torso twist rotation among the most proximal DOFs, elbow pronation/supination and wrist flexion/extension among DOFs in the left arm, and shoulder internal/external rotation and wrist flexion/extension among DOFs in the right arm. The contributions from pelvis obliquity, left wrist flexion/extension, left wrist ulnar/radial deviation and right shoulder flexion/extension differed significantly between the advanced and intermediate group.

  • 18.
    Tinmark, Fredrik
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Hellström, John
    Örebro universitet.
    Halvorsen, Kjartan
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Thorstensson, Alf
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Elite golfers' kinematic sequence in full-swing and partial-swing shots2010In: Sports Biomechanics, ISSN 1476-3141, Vol. 9, no 4, p. 236-244Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to investigate whether kinematic proximal-to-distal sequencing (PDS) and speed-summation are common characteristics of both partial and full-swing shots in golf players of different skill levels and genders. A total of 45 golfers participated, 11 male tournament professionals, 21 male and 13 female elite amateurs. They performed partial shots with a wedge to targets at three submaximal distances, 40, 55 and 70 m, and full-swing shots with a 5 iron and a driver for maximal distance. Pelvis, upper torso and hand movements were recorded in 3D with an electromagnetic tracking system (Polhemus Liberty) at 240 Hz and the magnitude of the resultant angular velocity vector of each segment was computed. The results showed a significant proximal-to-distal temporal relationship and a concomitant successive increase in maximum (peak) segment angular speed in every shot condition for both genders and levels of expertise. A proximal-to-distal utilization of interaction torques is indicated. Using a common PDS movement strategy in partial and full-swing golf shots appears beneficial from mechanical and control points of view and could serve the purpose of providing both high speed and accuracy.

  • 19.
    Åberg, Anna Cristina
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Frykberg, Gunilla Elmgren
    Halvorsen, Kjartan
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Medio-lateral stability of sit-to-walk performance in older individuals with and without fear of falling.2010In: Gait & Posture, ISSN 0966-6362, E-ISSN 1879-2219, Vol. 31, no 4, p. 438-43Article in journal (Refereed)
    Abstract [en]

    Most falls in older people are due to loss of balance during everyday locomotion, e.g., when initiating walking from sitting; sit-to-walk (STW). It has been considered that the broader stride width in walking that is seen in many people with fear of falling (FoF) does not increase stability, but could be predictive of future falls because of increased medio-lateral (ML) velocity of the body centre of mass (CoM). This study was aimed to examine step-, velocity- and stability-related parameters, focusing on ML stability, in STW performance of people with and without FoF. Ten subjects with FoF and 10 matched controls, aged > or = 70 years, were included. Kinematic and kinetic data were collected in a laboratory. Stability parameters were calculated from a formula implying that the vertical projection of the CoM extrapolated by adding its velocity times a factor radicall/g (height of inverted pendulum divided by gravity) should fall within the base of support (BoS). A related spatial margin of stability (SMoS), defined as the minimum distance from the extrapolated CoM (XCoM) to the boundaries of the BoS, was also calculated. In the phase 'seat-off-second-toe-off', the FoF group had significantly (p<0.05) shorter and broader steps, lower forward but similar ML CoM velocity, and broader CoM and XCoM widths. The FoF group therefore exhibited a disproportionately large sideways velocity compared to the controls. This indicates that STW may be a hazardous transfer for older people with FoF, which should be relevant in assessment and training aimed at preventing falls.

  • 20.
    Åberg, Anna Cristina
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Thorstensson, Alf
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Tarassova, Olga
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.
    Halvorsen, Kjartan
    School of Technology and Health, KTH-Royal Institute of Technology, Stockholm, Sweden.
    Calculations of mechanisms for balance control during narrow and single-leg standing in fit older adults: A reliability study.2011In: Gait & Posture, ISSN 0966-6362, E-ISSN 1879-2219, Vol. 34, no 3, p. 352-7Article in journal (Refereed)
    Abstract [en]

    For older people balance control in standing is critical for performance of activities of daily living without falling. The aims were to investigate reliability of quantification of the usage of the two balance mechanisms M1 ‘moving the centre of pressure’ and M2 ‘segment acceleration’ and also to compare calculation methods based on a combination of kinetic (K) and kinematic (Km) data, (K–Km), or Km data only concerning M2. For this purpose nine physically fit persons aged 70–78 years were tested in narrow and single-leg standing. Data were collected by a 7-camera motion capture system and two force plates. Repeated measure ANOVA and Tukey's post hoc tests were used to detect differences between the standing tasks. Reliability was estimated by ICCs, standard error of measurement including its 95% CI, and minimal detectable change, whereas Pearson's correlation coefficient was used to investigate agreement between the two calculation methods. The results indicated that for the tasks investigated, M1 and M2 can be measured with acceptable inter- and intrasession reliability, and that both Km and K–Km based calculations may be useful for M2, although Km data may give slightly lower values. The proportional M1:M2 usage was approximately 9:1, in both anterio-posterior (AP) and medio-lateral (ML) directions for narrow standing, and about 2:1 in the AP and of 1:2 in the ML direction in single-leg standing, respectively. In conclusion, the tested measurements and calculations appear to constitute a reliable way of quantifying one important aspect of balance capacity in fit older people.

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