Anna Bjerkefors

Deep and superficial abdominal muscle activation during trunk stabilization exercises with and without instruction to hollow.

The deepest muscle of the human ventro-lateral abdominal wall, the Transversus Abdominis (TrA), has been ascribed a specific role in spine stabilization, which has motivated special core stability exercises and hollowing instruction to specifically involve this muscle. The purpose here was to evaluate the levels of activation of the TrA and the superficial Rectus Abdominis (RA) muscles during five common stabilization exercises performed in supine, bridging and four-point kneeling positions, with and without instruction to hollow, i.e. to continuously pull the lower part of the abdomen towards the spine. Nine habitually active women participated and muscle activity was recorded bilaterally from TrA and RA with intramuscular fine-wire electrodes introduced under the guidance of ultrasound. Results showed that subjects were able to selectively increase the activation of the TrA, isolated from the RA, with the specific instruction to hollow and that side differences in the amplitude of TrA activity, related to the asymmetry of the exercises, remained even after the instruction to hollow. The exercises investigated caused levels of TrA activation from 4 to 43% of that during maximal effort and can thus be used clinically to grade the load on the TrA when designing programs aiming at training that muscle.

TRUNK MUSCLE ACTIVATION IN A PERSON WITH CLINICALLY COMPLETE THORACIC SPINAL CORD INJURY

OBJECTIVE The aim of this study was to assess if, and how, upper body muscles are activated in a person with high thoracic spinal cord injury, clinically classified as complete, during maximal voluntary contractions and in response to balance perturbations. METHODS Data from one person with spinal cord injury (T3 level) and one able-bodied person were recorded with electromyography from 4 abdominal muscles using indwelling fine-wire electrodes and from erector spinae and 3 upper trunk muscles with surface electrodes. Balance perturbations were carried out as forward or backward support surface translations. RESULTS The person with spinal cord injury was able to activate all trunk muscles, even those below the injury level, both in voluntary efforts and in reaction to balance perturbations. Trunk movements were qualitatively similar in both participants, but the pattern and timing of muscle responses differed: upper trunk muscle involvement and occurrence of co-activation of ventral and dorsal muscles were more frequent in the person with spinal cord injury. CONCLUSION These findings prompt further investigation into trunk muscle function in paraplegics, and highlight the importance of including motor tests for trunk muscles in persons with thoracic spinal cord injury, in relation to injury classification, prognosis and rehabilitation.

Dynamic trunk stability is improved in paraplegics following kayak ergometer training.

The purpose of the study was to assess whether postural stability in persons with spinal cord injury (SCI) could be affected by training. Ten post‐rehabilitated persons with thoracic SCI performed 30 sessions of kayak ergometer training during a 10‐week period. The ergometer was modified with a balance module adjustable in the medio‐lateral direction. Before and after the training period, horizontal support‐surface translations were presented randomly, either in the forward or backward direction, or to the side, while subjects sat in their own wheelchairs. The platform perturbation consisted of an unpredictable initial acceleration, followed by a constant‐velocity phase and a predictable deceleration. Markers were applied on the trunk and movement data were recorded in 3D. Four kinematic responses of trunk angular and linear displacement were investigated. In general, postural stability was improved after training with smaller rotational and linear displacements of the trunk observed during both predictable and unpredictable translations in all directions. Thus, the training was able to improve the ability of persons with long‐standing SCI to maintain an upright sitting posture in response to externally generated balance perturbations, which should imply an increased capacity to master similar challenges to balance in everyday life.

Sitting balance and effects of kayak training in paraplegics.

OBJECTIVES The objectives of this study were to evaluate biomechanical variables related to balance control in sitting, and the effects of kayak training, in individuals with spinal cord injury. SUBJECTS Twelve individuals with spinal cord injury were investigated before and after an 8-week training period in open sea kayaking, and 12 able-bodied subjects, who did not train, served as controls. METHODS Standard deviation and mean velocity of centre of pressure displacement, and median frequency of centre of pressure acceleration were measured in quiet sitting in a special chair mounted on a force plate. RESULTS All variables differed between the group with spinal cord injury, before training, and the controls; standard deviation being higher and mean velocity and median frequency lower in individuals with spinal cord injury. A significant training effect was seen only as a lowering of median frequency. CONCLUSION The results indicate that individuals with spinal cord injury may have acquired and consolidated an alternative strategy for balance control in quiet sitting allowing for only limited further adaptation even with such a vigorous training stimulus as kayaking.

Cortical and vestibular stimulation reveal preserved descending motor pathways in individuals with motor-complete spinal cord injury.

OBJECTIVE To use a combination of electrophysiological techniques to determine the extent of preserved muscle activity below the clinically-defined level of motor-complete spinal cord injury. METHODS Transcranial magnetic stimulation and vestibular-evoked myogenic potentials were used to investigate whether there was any preserved muscle activity in trunk, hip and leg muscles of 16 individuals with motor-complete spinal cord injury (C4-T12) and 16 able-bodied matched controls. RESULTS Most individuals (14/16) with motor-complete spinal cord injury were found to have transcranial magnetic stimulation evoked, and/or voluntary evoked muscle activity in muscles innervated below the clinically classified lesion level. In most cases voluntary muscle activation was accompanied by a present transcranial magnetic stimulation response. Furthermore, motor-evoked potentials to transcranial magnetic stimulation could be observed in muscles that could not be voluntarily activated. Vestibular-evoked myogenic potentials responses were also observed in a small number of subjects, indicating the potential preservation of other descending pathways. CONCLUSION These results highlight the importance of using multiple electrophysiological techniques to assist in determining the potential preservation of muscle activity below the clinically-defined level of injury in individuals with a motor-complete spinal cord injury. These techniques may provide clinicians with more accurate information about the state of various motor pathways, and could offer a method to more accurately target rehabilitation.

EFFECTS oF SEATED DoublE-PolINg ERgoMETER TRAININg oN AERobIC AND MEChANICAl PowER IN INDIVIDuAlS wITh SPINAl CoRD INJuRy

OBJECTIVE To determine whether regular interval training on a seated double-poling ergometer can increase physical capacity and safely improve performance towards maximal level in individuals with spinal cord injury. METHODS A total of 13 subjects with spinal cord injury (injury levels T5-L1) performed 30 sessions of seated double-poling ergometer training over a period of 10 weeks. Sub-maximal and maximal double-poling ergometer tests were performed before (test-retest) and after this training period. Oxygen uptake was measured using the Douglas Bag system. Three-dimensional kinematics were recorded using an optoelectronic system and piezoelectric force sensors were used to register force in both poles. RESULTS The mean intra-class correlation coefficient for test-retest values was 0.83 (standard deviation 0.11). After training significant improvements were observed in people with spinal cord injury in oxygen uptake (22.7%), ventilation (20.7%) and blood lactate level (22.0%) during maximal exertion exercises. Mean power per stroke and peak pole force increased by 15.4% and 23.7%, respectively. At sub-maximal level, significantly lower values were observed in ventilation (-12.8%) and blood lactate level (-25.0%). CONCLUSION Regular interval training on the seated double-poling ergometer was effective for individuals with spinal cord injury below T5 level in terms of improving aerobic capacity and upper-body power output. The training was safe and did not cause any overload symptoms.

Seated Double-Poling Ergometer Performance of Individuals with Spinal Cord Injury - A New Ergometer Concept for Standardized Upper Body Exercise

This study aimed to evaluate biomechanics during seated double-poling exercises in individuals with spinal cord injury (SCI) and to compare these with those of able-bodied persons (AB). 26 participants volunteered for the study; 13 with SCI (injury levels C7-T12), and 13 AB. A seated double-poling ergometer (SDPE) was developed. 3-dimensional kinematics was measured and piezoelectric force sensors were used to register force in both poles for calculation of power during incremental intensities. Significantly lower power outputs, (143.2 ± 51.1 vs. 198.3 ± 74.9 W) and pole forces (137.1 ± 43.1 vs. 238.2 ± 81.2 N) were observed during maximal effort in SCI compared to AB. Sagittal upper trunk range of motion increased with intensity and ranged from 6.1-34.8° for SCI, and 6.9-31.3° for AB, with larger peak amplitudes in flexion for AB (31.4 ± 12.9°) compared to SCI (10.0 ± 8.0°). All subjects with SCI were able to exercise on the SDPE. Upper body kinematics, power and force outputs increased with intensity in both groups, but were in general, lower in SCI. In conclusion, the SDPE could be successfully used at low to high work intensities enabling both endurance and strength training for individuals with SCI.

ASSESSMENT OF ABDOMINAL MUSCLE FUNCTION IN INDIVIDUALS WITH MOTOR-COMPLETE SPINAL CORD INJURY ABOVE T6 IN RESPONSE TO TRANSCRANIAL MAGNETIC STIMULATION

OBJECTIVE To use transcranial magnetic stimulation and electromyography to assess the potential for preserved function in the abdominal muscles in individuals classified with motor-complete spinal cord injury above T6. SUBJECTS Five individuals with spinal cord injury (C5-T3) and 5 able-bodied individuals. METHODS Transcranial magnetic stimulation was delivered over the abdominal region of primary motor cortex during resting and sub-maximal (or attempted) contractions. Surface electromyography was used to record motor-evoked potentials as well as maximal voluntary (or attempted) contractions in the abdominal muscles and the diaphragm. RESULTS Responses to transcranial magnetic stimulation in the abdominal muscles occurred in all spinal cord injury subjects. Latencies of muscle response onsets were similar in both groups; however, peak-to-peak amplitudes were smaller in the spinal cord injury group. During maximal voluntary (or attempted) contractions all spinal cord injury subjects were able to elicit electromyography activity above resting levels in more than one abdominal muscle across tasks. CONCLUSION Individuals with motor-complete spinal cord injury above T6 were able to activate abdominal muscles in response to transcranial magnetic stimulation and during maximal voluntary (or attempted) contractions. The activation was induced directly through corticospinal pathways, and not indirectly by stretch reflex activations of the diaphragm. Transcranial magnetic stimulation and electromyography measurements provide a useful method to assess motor preservation of abdominal muscles in persons with spinal cord injury.

Three-dimensional kinematic analysis and power output of elite flat-water kayakers

Abstract The purpose was to examine power output and three-dimensional (3D) kinematic variables in the upper limbs, lower limbs and trunk in elite flat-water kayakers during kayak ergometer paddling. An additional purpose was to analyse possible changes in kinematics with increased intensity and differences between body sides. Six male and four female international level flat-water kayakers participated. Kinematic and kinetic data were collected during three tasks; low (IntL), high (IntH) and maximal (IntM) intensities. No differences were observed in any joint angles between body sides, except for shoulder abduction. Significantly greater range of motion (RoM) values were observed for IntH compared to IntL and for IntM compared to IntL in trunk and pelvis rotation, and in hip, knee and ankle flexion. The mean maximal power output was 610 ± 65 and 359 ± 33 W for the male and female athletes, respectively. The stroke frequencies were significantly different between all intensities (IntL 59.3 ± 6.3; IntH 108.0 ± 6.8; IntM 141.7 ± 18.4 strokes/min). The results showed that after a certain intensity level, the power output must be increased by other factors than increasing the joint angular RoM. This information may assist coaches and athletes to understand the relationship between the movement of the kayaker and the paddling power output.

Three-Dimensional Kinematics and Power Output in Elite Para-Kayakers and Elite Able-Bodied Flat-Water Kayakers

Trunk, pelvis, and leg movements are important for performance in sprint kayaking. Para-kayaking is a new Paralympic sport in which athletes with trunk and/or leg impairment compete in 3 classification groups. The purpose of this study was to identify how physical impairments impact on performance by examining: differences in 3-dimensional joint range of motion (RM) between 10 (4 females and 6 males) elite able-bodied kayakers and 41 (13 females and 28 males) elite para-kayakers from the 3 classification groups, and which joint angles were correlated with power output during high-intensity kayak ergometer paddling. There were significant differences in RM between the able-bodied kayakers and the 3 para-kayak groups for the shoulders (flexion, rotation: able-bodied kayakers < para-kayakers); trunk and pelvis (rotation: able-bodied kayakers > para-kayakers); and legs (hip, knee, and ankle flexion: able-bodied kayakers > para-kayakers) during paddling. Furthermore, athletes with greater impairment exhibited lower trunk and leg RM compared with those with less impairment. Significant positive correlations were observed for both males and females between power output and peak shoulder and trunk flexion; trunk and pelvis rotation RM; and hip, knee, and ankle flexion RM. This information is important for understanding how key kinematic and kinetic variables for para-kayaking performance vary between athletes from different classification groups.