Papers by Kjartan Halvorsen
The purpose of this study was to investigate ground reaction forces during long jump take-off for... more The purpose of this study was to investigate ground reaction forces during long jump take-off for lower limb amputees. Elite transtibial amputee (n=3) and able-bodied (n=6) athletes performed six running long jumps in an indoor athletics stadium with a force plate sunk into the runway. For each athletes' longest jump, vertical (Fz) and horizontal (Fy) peak forces and impulses were calculated. The amputees had a shorter braking impulse duration, followed by a longer propulsive impulse duration with greater peak horizontal propulsive force and impulse than the able-bodied athletes. Vertical loading force and rate of force development at take-off was smaller for the amputees. It may be that amputees attempt to conserve as much horizontal velocity as possible by braking briefly, providing a longer duration in which to apply propulsive forces.
Journal of Biomechanics, 2003
It is shown that a recently published least squares method for the estimation of the average cent... more It is shown that a recently published least squares method for the estimation of the average center of rotation is biased. Consequently, a correction term is proposed, and an iterative algorithm is derived for finding a bias compensated solution to the least squares problem.The accuracy of the proposed bias compensated least squares method is compared to the previously proposed least squares method by Monte-Carlo simulations. The tests show that the new method gives a substantial improvement in accuracy.
Journal of Biomechanics, 2009
A new method is proposed for finding small sets of points on the body giving sufficient informati... more 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 1-2 cm), and moderate errors in AM (13-20% of peak value).
Journal of Biomechanics, 2010
Gait & Posture, 2008
Gymnasts are known to practice and compete although suffering from injuries and pain. Pain may ch... more 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.
British Journal of Sports Medicine, 2007
To compare the efficacy and safety of two eccentric rehabilitation protocols for patients with sy... more 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. Prospective, randomised clinical trial. Sports rehabilitation clinic, university sports laboratory, supplemented with home exercises. 20 competitive and recreational athletes, all with clinical diagnosis of patellar tendinopathy, verified by MRI or ultrasound imaging. 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. 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. 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. 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.
Journal of biomechanics, Jan 7, 2014
The concept of mobility describes an important property of the human body when performing manipul... more The concept of mobility describes an important property of the human body when performing manipulation tasks. It describes, in a sense, how easy it is to accelerate a link or a point on the manipulator. Most often it is calculated for the end-link or end-point of the manipulator, since these are important for the control objective of the manipulator. Mobility is the inverse of the inertia experienced by a force acting on the end-point, or a combined force and torque acting on the end-link. The concept has been used in studies of reaching tasks with one arm, but thus far not for bi-manual manipulation. We present here the concept for both single-handed and double-handed manipulation, in a general manner which includes any type of grip of the hands on the object. The use of the concept is illustrated with data on the left and right arm in a golf swing.
Scandinavian journal of medicine & science in sports, 2009
Eccentric exercises are commonly used as a treatment for various muscle and tendon injuries. Duri... more 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 t...
Page 1. Analysis of elite golfers' kinematic sequence in full and partial shots Fredrik Tinm... more Page 1. Analysis of elite golfers' kinematic sequence in full and partial shots Fredrik Tinmark THE SWEDISH SCHOOL OF SPORT AND HEALTH SCIENCES (GIH) Thesis for the degree of master 17:2007 Supervisor: Kjartan Halvorsen, PhD Page 2. Abstract Aim ...
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Papers by Kjartan Halvorsen