Short-term effects of backpack load placement on spine deformation and repositioning error in schoolchildren.

Backpack weight of 10-15% has been recommended as an acceptable limit for schoolchildren. However, there is still no clear guideline regarding where the backpack centre of gravity (CG) should be positioned. The changes of spinal curvature and repositioning error when carrying a backpack loaded at 15% of body weight at different CG locations (anterior or posterior at T7, T12 or L3) in schoolchildren were analysed. Both spinal curvature and repositioning error were found to be affected by backpack anterior-posterior position and CG level. A relatively smaller change was observed during anterior carriage with the least change when the backpack CG was positioned at T12. The results also suggested that alternative carriage by changing the backpack position occasionally between anterior and posterior positions might help to relieve the effects of backpack on spine. However, future study is recommended to further substantiate the beneficial effects of alternative carriage on children. STATEMENT OF RELEVANCE: Anteriorly carried backpack with centre of gravity positioned at T12 was shown to induce relatively less effect on spinal deformation and repositioning error in schoolchildren. Changing backpack carriage position occasionally may help to relieve its effects on spinal deformation. The findings are important for ergonomic schoolbag design and determining a proper load carriage method.

Effects of electroacupuncture on a degenerated intervertebral disc using an in-vivo rat-tail model.

Electroacupuncture (EA) has long been used as conservative treatment for low back pain (LBP). Its effect on relief of back pain has been demonstrated in many clinical studies. However, whether it has any effect on the biological properties of an intervertebral disc, which is one of the major causes of LBP, is still unclear. The aim of this study was, therefore, to investigate the effects of EA with different simulation frequencies on an intervertebral disc with simulated degeneration using an in-vivo rat-tail model. In this study, 33 rats were used. Disc degeneration was simulated in the rat caudal 8-9 disc via continuous static compressive loading of 11 N for 2 weeks. EA with a frequency of 2 or 100 Hz was then applied to the degenerated disc for 3 weeks with 3 sessions/week and 20 min/session. The intervertebral disc height was measured before and after compression as well as after EA intervention for 3 weeks. The static compression was found to result in a reduction in the disc height of about 22 per cent. There was no evidence that this change could be reversed after resting or the EA intervention. However, EA at 100 Hz was found to induce a further decrease in disc height, which was not shown for the rats after resting or EA at 2 Hz. The results of this study showed that effects of EA on disc degeneration are frequency dependent and adverse effects could result if EA at a certain frequency was used.

Effects of whole body vibration on spinal proprioception in healthy individuals.

BACKGROUND: Low back pain (LBP) is a common health problem with high reoccurrence rate. As patients with LBP are often found to be proprioception impaired, new proprioception exercises should be explored. Whole body vibration (WBV) has been proven to improve muscle function and proprioception. OBJECTIVE: The aim of this study was to determine the effects of WBV on spinal proprioception when WBV was administered in standing and seated postures. METHODS: Twenty healthy male individuals (mean age: 23.2±1.2 years) were recruited and randomly assigned to two WBV groups: WBV in standing or WBV in seated posture. Their body posture, lumbar repositioning ability, maximum reaching distance and lumbopelvic coordination during dynamic motion in flexion and extension were assessed before, immediately after, 30 minutes after and 1 hour after 5 minutes of WBV (18 Hz, 6 mm amplitude) exposure. A Mixed ANOVA was used to analyze the effects of group and time factors on these four outcome measures. RESULTS: There were no significant interaction (group and time) and group effects on all outcome measures. Participants were found to have significant different time effect on body posture, lumbar repositioning ability, maximum reaching distance and lumbopelvic coordination. CONCLUSIONS: WBV could significantly improve spinal proprioception including body posture, lumbar repositioning ability, maximum reaching distance and lumbopelvic coordination in healthy individuals. WBV protocol is recommended to confirm its clinical application for improving spinal proprioception and its effects on patients with LBP is warranted.

Effect of an on-hip load-carrying belt on physiological and perceptual responses during bimanual anterior load carriage.

Manual load carriage continues to be a major contributor of musculoskeletal injury. This study investigates the physiological and subjective effects of an on-hip load-carrying belt (HLCB) during bimanual anterior load carriage. Fifteen healthy male participants walked on a level ground treadmill at 4.5 km/h for 5 min carrying 5, 10 and 15 kg loads with hands and arms in front of the body, with and without using the HLCB (WD and ND). Heart rate, normalized oxygen uptake, minute ventilation and, central and peripheral ratings of perceived exertion were the dependent variables. The mean heart rate, normalized oxygen uptake, minute ventilation and peripheral rating of perceived exertion increased significantly with load under both WD and ND conditions. At a load of 15 kg, the mean heart rate, normalized oxygen uptake, minute ventilation and peripheral rating of perceived exertion were significantly lower by 6.6%, 8.0%, 11.8% and 13.9% respectively in WD condition when compared to the ND condition. There was no significant difference between WD and ND conditions with 5 or 10 kg load. It can be concluded that the HLCB could reduce a person's physiological and peripheral perceptual responses when walking on a level ground treadmill at 4.5 km/h with a load of 15 kg. Using a HLCB or similar device is therefore recommended for bimanual anterior load carriage for loads of 15 kg or probably larger.

Active finite element analysis of skeletal muscle-tendon complex during isometric, shortening and lengthening contraction.

An active finite element model was developed to predict the mechanical behaviors of skeletal muscle-tendon complex during isometric, shortening and lengthening contraction. The active finite element was created through incorporation of a user-defined material property into ABAQUS finite element code. The active finite element is controlled by a motor element that is activated by a mathematical function. The nonlinear passive behavior of the muscle was defined by the viscoelastic elements and can be easily altered to other properties by using other elements in the material library without the need of re-defining the constitutive relation of the muscle. The isometric force-length relationship, force-strain relations of the muscle-tendon complex during both shortening and lengthening contraction and muscle relaxation response were predicted using the proposed finite element model. The predicted results were found to be in good agreement with available experimental data. In addition, the stress distribution in the muscle-tendon complex during isometric, shortening and lengthening contractions was simulated. The location of the maximum stress may provide useful information for studying muscle damage and fatigue in the future.

Effects of whole body vibration on spinal proprioception in normal individuals.

Low back pain (LBP) is a common health problem with high reoccurrence rate. While most LBP cases are classified as non-specific, patients in general often present impaired proprioception. Whole body vibration (WBV) has been proven to improve muscle function and proprioception in the lumbo-pelvic region. The aim of this study was to determine whether WBV would affect spinal proprioception. Eleven young normal individuals were recruited. Their body alignment, lumbar repositioning error and lumbo-pelvic coordination during dynamic motion were assessed before and after 5 minutes WBV (18 Hz, 6 mm amplitude). Assessments were conducted before, immediately after, 30 minutes after and 1 hour after WBV. Subjects were found to have improved lumbo-pelvic coordination and flexibility without any adverse effect on the neuromuscular system after WBV. However, WBV had no significant immediate effect on lumbar repositioning ability and body alignment. Future studies of the effects of different WBV protocols on LBP patients are recommended.

Comfort evaluation of maternity support garments in a wear trial.

This study aims to evaluate the wear comfort of eight commercially available maternity support garments. The thermophysiological, sensory/tactile and movement comfort were assessed in a wear trial using a 19-item questionnaire. Fourteen pregnant Chinese women aged 32.3 +/- 4.2 years were recruited from a local obstetric clinic. The results show that the tested garments generally provided greater sensory comfort than thermophysiological comfort. The thermophysiological comfort was mainly influenced by the fibre contents and breathability. Significant linear relationships were found between material appearance and hand feel (r = 0.86, p < 0.001), and between non-itchiness and no red mark (r = 0.78, p < 0.001). Movement comfort was influenced by the garment type and style features. Overall, the soft, good-fit, cotton/elastane maternity brief was perceived as the best product. The findings of comfort needs in pregnant women and the effects of various garment attributes would be helpful for the development of maternity support garment design criteria that are required to satisfy critical ergonomic needs. Low back pain during pregnancy is a common and significant health problem. A maternity support garment is regarded as a convenient and safe device to stabilise the lumbar spine so as to relieve pain. However, patient compliance is likely to be affected by discomfort and inconvenience. The results of this study provide guidance for the optimal design of maternity support clothing.

Changes in spinal curvature and proprioception of schoolboys carrying different weights of backpack.

Despite evidence linking backpack carriage and back pain, previous studies to examine the effects of backpack carriage have focused on changes in physical performance rather than the direct effects on the spine itself. Spinal curvature and proprioception (in terms of spinal repositioning consistency) of 15 schoolboys during normal upright stance without a backpack and while carrying a specially adapted backpack loaded at 10, 15 and 20% of their bodyweight were measured and compared using repeated measures ANOVA. A significant flattening of the lumbar lordosis and the upper thoracic kyphosis was found with increasing backpack load, as well as a significant decrease in the thoraco-lumbar and lumbar repositioning consistencies. Carriage of a loaded backpack causes immediate changes in spinal curvature and appears to have a direct effect on the repositioning consistency. Further investigation of the changes in spinal curvature and repositioning consistency over time with prolonged backpack carriage is warranted. Daily carriage of a school backpack on the musculoskeletal health of children and adolescents has become an area of concern due to the association between backpack carriage and back pain. Data regarding the direct effect of backpack carriage on the spine in children are limited.

The feasibility of repositioning ability as a tool for ergonomic evaluation: effects of chair back inclination and fatigue on head repositioning.

Poor posture has been suggested as one of the main factors contributing to the high prevalence of neck pain in video display unit (VDU) users, but no clear association between pain and any particular resting neck posture has been found. Postural awareness of the neck, as indicated by the repositioning accuracy, may therefore be an appropriate measure and potentially useful assessment tool. The objective of this study is to examine whether posture and fatigue affect the head repositioning ability in typical VDU usage. A group of 20 healthy participants reproduced a normal comfortable posture for forward, upright and backward chair back inclinations in random order both before and after fatigue of the upper trapezius muscles. Ten repetitions of the posture were recorded for 2 s each, and the angular and translational deviations from the original head position were measured with regard to the external environment (head in space repositioning) and with regard to the trunk (head on trunk repositioning). Analysis by repeated measures ANOVA showed significant effects and interactions of fatigue and chair back inclination on the repositioning errors in the sagittal plane, which typically showed systematic trends towards certain postures rather than random errors around a mean position. While further work is required to examine the ergonomic impact of impaired repositioning ability, head repositioning is sensitive to ergonomic factors such as seating configuration and fatigue, and may therefore be a useful tool for evaluation of static working postures.