Weight knowledge and weight magnitude: impact on lumbosacral loading

Influence of load knowledge on lifting biomechanics

Objectives. Findings from previous studies implied that appropriately controlling load knowledge might help improve the biomechanical performance during lifting tasks. However, only load weight knowledge was often discussed in previous studies. The current study aimed to complement the existing studies and provide improved knowledge about the influence of load knowledge on lifting biomechanics. Methods. Twenty-four healthy male participants were recruited and instructed to perform symmetric lifting tasks with different load weights under different load knowledge conditions. Load weights were set at three levels (40, 80 and 120%) of each participant's maximum acceptable lifting capacity. The examined load knowledge conditions included 'no knowledge' condition, 'weight known' condition, 'fragile material known' condition and 'weight and fragile material known' condition. Results. We found that when knowing fragility information about lifting materials, workers tended to be more cautious by adopting a less dynamic motion pattern during the landing phase, as evidenced by decreases of 6-8% in elbow joint acceleration. The 'cautious' lifting pattern when fragility load knowledge was presented could contribute to reduced risk of lower back disorder. Conclusion. This finding could help to develop lower back disorder prevention interventions to improve occupational safety and health.

Older adults utilize less efficient postural adaptations when they are uncertain about the magnitude of a perturbation

People frequently experience perturbations while standing or walking in crowded areas or when interacting with external objects. Balance maintenance in response to a perturbation is affected by the predictability of the magnitude of a body disturbance. The aim of this quasi-experimental study was to investigate the role of aging in maintenance of standing balance in response to perturbations of varying magnitudes. Twelve older adults and twelve young adults received a series of frontal perturbations of small or large magnitudes induced to their upper body by a pendulum impact while standing. The perturbation sequence included 10 trials of small, 15 trials of large, and 10 more trials of small magnitudes. The participants were exposed to either repetitive perturbations of known (predictable) magnitude or perturbations of unknown (unpredictable) magnitude as they were not told which of the perturbation magnitude (small, large) to expect. Electromyographic activity of six leg and trunk muscles and displacements of the center of pressure were recorded and analyzed during anticipatory (APAs) and compensatory (CPAs) phases of postural control. When exposed to both, repetitive perturbations of known magnitude and perturbations of unpredictable magnitude, older adults, compared to young adults, demonstrated delayed and smaller anticipatory and compensatory postural adaptations. Older adults also required more trials to modify postural adjustments, as compared to young adults. The findings imply that the ability to predict magnitudes of frontal perturbations is declined in older adults.

Influence of Load Knowledge on Biomechanics of Asymmetric Lifting

BACKGROUND

Load knowledge has been identified as a factor affecting the risk of low back pain (LBP) during symmetric lifting. However, the effects of load knowledge in asymmetric lifting tasks have not been reported yet. The purpose of this study was to investigate the load knowledge influence on lifting biomechanics in asymmetric lifting tasks; Methods: Twenty-four male adults were recruited to complete a psychophysical lifting capacity test and a simulated asymmetric lifting task. The lifting task was set with load knowledge of 'no knowledge' (NK), 'weight known' (WK), 'fragile material known' (FK), and 'weight and fragile material known' (WFK) for different lifting load weights. Trunk kinematics and kinetics were collected and analyzed; Results: When fragility information was presented, trunk sagittal flexion acceleration, lateral flexion velocity and acceleration, and average lateral bending moment were significantly lowered at the deposit phase. Lifting a high load weight was found to significantly increase low back sagittal bending moment at the lifting phase and low back moments of all three dimensions at the deposit phase; Conclusions: The decrease of trunk kinematic load suggests that providing material fragility information to workers in asymmetric lifting tasks would be effective in reducing their risk of LBP.

The Effect of Predictability of the Perturbation Magnitude on Anticipatory and Compensatory Postural Adjustments during a Bimanual Load-Lifting Task

Background: To minimize the potential postural disturbance induced by external or self-initiated perturbations, humans generate anticipatory postural adjustments based on their perceived consequences of the body disturbance. Lifting is a common activity that induces a self-initiated perturbation that can compromise balance control. Aim: To assess anticipatory (APAs) and compensatory (CPAs) postural adjustments generated in response to a self-initiated perturbation induced by lifting objects of uncertain mass. Methods: Ten young adults lifted the tray with either light or heavy object placed in it. Electromyographic activity of eight trunk and leg muscles, and center-of-pressure (COP) displacements were recorded and analyzed during the APAs and CPAs phases. Results: When the object mass changed unpredictably, the participants generated APAs based on the most recent experience of lifting and needed three trials of lifting to generate optimal APAs and CPAs. Conclusions: Young adults were able to predict the perturbation magnitude during self-initiated perturbations induced by lifting objects. The outcome provides a foundation for future studies focusing on the role of predictability of perturbation consequences in postural control of older adults and individuals with balance deficit.

Sagittal spine disposition and pelvic tilt during outdoor fitness equipment use and their associations with kinanthropometry proportions in middle-aged and older adults

BACKGROUND

Outdoor fitness training has become popular as a tool for improving the health, especially middle-aged and older adults. For this purpose, outdoor fitness equipment (OFE) have been installed in public areas. However, their safety and effectiveness are still unknown. The aim of the present research was to analyze the sagittal disposition of the spine and pelvic tilt during the use of OFE, and to determine the influence of anthropometric variables on these factors in middle-aged and older adults.

METHODS

Seventy healthy volunteers, 56 women and 14 men (age: 63.14 ± 8.19 years) participated in the study. Sagittal spine disposition and pelvic tilt were measured using a Spinal Mouse®, in the relaxed standing position, and during the use of the OFE. In addition, kinanthropometry variables were also measured according to the guidelines of the International Society for the Advancement of Kinanthropometry.

RESULTS

Regarding thoracic kyphosis, a significant decrease was found in thoracic kyphosis in the initial position (IP) in single bonny rider (SBR) (p = 0.006) and row (p = 0.046), and a significant increase in the final position (FP) in the row (p = 0.011), surfboard (p < 0.001) and air walker (p = 0.027) machines. In relation to the lumbar curvature and pelvic tilt, a significant decrease in lumbar lordosis and a decrease in pelvic anteversion were observed in the IP and FP in SBR and row; and in the bike (p < 0.001) machine. In the surfboard machine, a significant decrease in lumbar lordosis was found (p = 0.002), with no changes in pelvic tilt. According to the multiple linear regression analysis, the subjects with a higher cormic index and height were more at risk of increasing their thoracic kyphosis, decreasing lumbar lordosis and/or decreasing pelvic anteversion towards pelvic retroversion.

CONCLUSIONS

Middle-aged and older adults show spinal misalignments when using the OFE with respect to the standing position, showing a decrease in the thoracic kyphosis in IP of SBR and ROW, and a significant increase in the surfboard and air walker, and in the FP of Row, in the lumbar lordosis in all the OFE in sitting and some in standing, and in the pelvic anteversion in all the OFE in sitting. The variables height and the cormic index explained most of the changes in sagittal spine disposition.

Psychophysiological responses to manual lifting of unknown loads

BACKGROUND

The handling of unknown weights, which is common in daily routines either at work or during leisure time, is suspected to be highly associated with the incidence of low back pain (LBP).

OBJECTIVES

To investigate the effects of knowledge and magnitude of a load (to be lifted) on brain responses, autonomic nervous activity, and trapezius and erector spinae muscle activity.

METHODS

A randomized, within-subjects experiment involving manual lifting was conducted, wherein 10 participants lifted three different weights (1.1, 5, and 15 kg) under two conditions: either having or not having prior knowledge of the weight to be lifted.

RESULTS

The results revealed that the lifting of unknown weights caused increased average heart rate and percentage of maximum voluntary contraction (%MVC) but decreased average inter-beat interval, very-low-frequency power, low-frequency power, and low-frequency/high-frequency ratio. Regardless of the weight magnitude, lifting of unknown weights was associated with smaller theta activities in the power spectrum density (PSD) of the central region, smaller alpha activities in the PSD of the frontal region, and smaller beta activities in the PSDs of both the frontal and central regions. Moreover, smaller alpha and beta activities in the PSD of the parietal region were associated only with lifting of unknown lightweights.

CONCLUSIONS

Uncertainty regarding the weight to be lifted could be considered as a stress-adding variable that may increase the required physical demand to be sustained during manual lifting tasks. The findings of this study stress the importance of eliminating uncertainty associated with handling unknown weights, such as in the cases of handling patients and dispatching luggage. This can be achieved through preliminary self-sensing of the load to be lifted, or the cautious disclosure of the actual weight of manually lifted objects, for example, through clear labeling and/or a coding system.

The impact of forward head posture on the electromyographic activity of the spinal muscles

Objective

This study aims to examine the electromyographic activity of the regional spinal muscle between patients with forward head posture (FHP) and those with a normal cranio-vertebral (CV) angle.

Methods

We recruited 60 adult women aged between 18 and 29 years from a single institution. The CV angle was measured in the sagittal plane, which helped us to assign the participants in the FHP group (n = 30) with a large CV angle (53.1 ± 2.3) and the control group (n = 30) with a normal CV angle (43.0 ± 3.6). The surface electromyography (EMG) was used to measure the magnitude of normalised muscle activity of eight spinal muscles (cervical, lumbar, and thoracic levels) while standing and performing a specific manual handling task.

Results

The CV angle was significantly lower in the FHP group than in the control group (p = .001). The cervical erector spinae (CES) muscle activity was significantly increased in the FHP group compared to that in the control group. The right and left CES of those in the FHP group exhibited 73% and 87%, respectively, higher normalised muscle activity than those in the control group while performing the manual handling task (p = .001). No significant difference was detected for the thoracic or lumbar segment muscles between groups.

Conclusion

Our results indicate that greater neck muscle demands result from anterior head translation in FHP. This effect is a counterbalance to the reduced CV angle and to support the neck. The increased activity of the neck muscles in FHP could demand more support from the neck muscles and might increase the risk of spinal injuries. Management of FHP is essential to avoid overloading the spinal muscles.

Relationship between sagittal spinal curves geometry and isokinetic trunk muscle strength in adults

PURPOSE

Sagittal spinal deviation has been reported to be a significant musculoskeletal problem affecting both genders and could develop at any age. Factors triggering this issue are still not well defined. The purpose of this study was to investigate the relationship between sagittal spine angles and isokinetic peak, average torque, and power of trunk muscles in asymptomatic adults.

METHODS

A convenient sample of 79 subjects with asymptomatic spine participated in this study. Thoracic and lumbar curves angles were measured using the Formetric 4D device. Thoracolumbar (T/L) ratio was calculated as an indicator of spine balance. Isokinetic peak and average torque and average power for trunk flexors and extensors were measured at 60°/s in seated and semi-standing test positions.

RESULTS

Lumbar curve angle was moderately inversely correlated (p < 0.001) with peak extension torque (ρ = - 0.532 and - 0.495 in seated and semi-standing positions, respectively) and peak flexion torque (ρ = - 0.604 and - 0.542 in seated and semi-standing positions, respectively). The T/L ratio was found to be significantly associated (p < 0.001) with trunk extension torque (ρ = 0.422 and 0.378 in seated and semi-standing positions, respectively) and trunk flexion torque (ρ = 0.396 and 0.321 in seated and semi-standing positions, respectively). Similarly, average torque and power measurements were significantly correlated with lumbar curve angle and T/L ratio.

CONCLUSIONS

Sagittal spine balance is associated with trunk muscles strength in adults, particularly, the lumbar spine muscles. Therefore, assessment of sagittal spinal balance and trunk muscles strength should be taken into consideration when designing rehabilitation programs for correction of sagittal spine curvature.