A comparative analysis of lumbar spine mechanics during barbell- and crate-lifting: implications for occupational lifting task assessments

Quantifying how functional and structural personal factors influence biomechanical exposures in paramedic lifting tasks

It is unknown how structural (sex, stature, body mass) and functional (strength, flexibility) personal factors influence lifting strategy in paramedic work. We explored whether variance in peak low back forces and kinematic coordination patterns could be explained by structural and functional personal factors in paramedic lifting tasks. Seventy-two participants performed backboard and stretcher lifts. Peak low back forces normalised to body mass, as well as kinematic coordination patterns, were calculated as dependent variables. Being female, stronger, shorter, having higher body mass, and/or having greater lower body range of motion (ROM) were all independently associated with lower normalised low back forces across backboard and stretcher lifting. Females and stronger individuals seemed to define a movement objective to consistently minimise compressive forces, while individuals with greater hip ROM consistently minimised anteroposterior shear forces. The efficacy of improving strength and hip ROM to reduce low back forces in paramedic lifting should be investigated.Practitioner summary: Females, stronger individuals, and individuals with greater hip range of motion consistently exhibited lower normalised low back forces in paramedic lifting. Improving strength and hip range of motion via training is a potential proactive ergonomics approach to reduce peak low back forces in paramedic lifting tasks.

Transient Electromyographic Responses by Isokinetic Torque Release during Mechanically Assisted Elbow Flexion

Power assistance on joint torque may not be beneficial to all the related muscles. We investigated the effects of power assistance on torque release during isokinetic elbow flexion. An isokinetic dynamometer system was used to simulate dynamic elbow flexion with power assistance, which altered the exercise conditions of baseline isometric torque (greater and lower) and rotation speed (faster and slower) of the lever arm. Ten male right-handed participants performed exercise tasks using the system. We measured (1) the electromyogram (EMG) amplitudes of the biceps brachii (BB), brachioradialis (BR), and triceps brachii (TB) muscles, (2) torque output and its variability, and (3) the perceived assistance level. Transient responses of the objective measurements were analyzed by observing three time epochs before and after power assistance. Greater variability and lower perceived assistance levels were observed when greater torque was released at a faster rotation speed. The torque output and EMG amplitudes of BB and BR muscles decreased over time. However, EMG amplitudes in the TB muscle were relatively constant until 200 ms after power assistance resulting in greater muscle co-contraction. This could be attributed to the increased postural stability of the human musculature system when the external perturbation on joint movement occurred by power assistance, independent of exercise conditions.

Virtual modelling and analysis of manual material handling activities among warehouse workers in the construction industry

BACKGROUND: Musculoskeletal risks (MSRs) are a major concern among construction warehouse workers due to the lifting, carrying and lowering of heavy loads. OBJECTIVE: The objective of this study was to reduce MSRs among warehouse workers in the construction industry using virtual modelling and analysis of activities. METHODS: A preliminary study was carried out using the Standard Nordic Questionnaire. Biomechanical analysis, Ovako Working posture Assessment System (OWAS) and Rapid Upper Limb Assessment (RULA) were used to analyse the material handling activities. Virtual modelling was used develop the manikins with autoclaved aerated concrete (AAC) blocks at different carriage modes and stacking heights for the analysis. RESULTS: The preliminary study results revealed a higher prevalence of risk at their lower back (73.24%) among the construction warehouse workers. Biomechanical analysis showed a higher risk at L4-L5 joint of lumbar spine during overhead and bending postures for stacking the blocks. Posture analysis results of OWAS indicated a lower risk in overhead carriage mode. Detailed analysis with RULA confirms this result. Mean compressive force values at stacking heights were showed a significant difference (p < 0.05) in 8, 13, 18 and 21 kg AAC blocks. However, stacking height with a range of 120–140 cm was found as safer to the workers by considering all block sizes. CONCLUSION: An ergonomic intervention based on safer stacking heights was developed to reduce MSRs to an acceptable range. It improves productivity of handling the AAC blocks by reducing the cycle time. The intervention can be adapted for handling of similar materials in the construction industry.

Reconstructing an accelerometer-based pelvis segment for three-dimensional kinematic analyses during laboratory simulated tasks with obstructed line-of-sight

Close interface between humans and inanimate objects (furniture, assistive devices, and external loads) can obstruct line-of-sight in biomechanics studies that utilize optoelectronic motion capture systems. This specific problem is frequently encountered with the pelvis segment. This study sought to compare joint and pelvis angles computed from a pelvis-fixed local coordinate system (LCS) that was constructed from optically tracked pelvis landmarks (gold standard) and landmarks derived from angular deviations calculated from triaxial accelerometer data. One participant performed seven tasks: sitting, forward bend, sit-to-stand-to-sit, forward lunge, symmetrical squat, asymmetrical squat, and gait. The root mean square error (RMSE) and coefficient of determination (R²) were examined for the pelvis, lumbar spine, and hip joint angles calculated using the standard and accelerometer-based methods for creating a LCS. The RMSE values for global pelvis angles ranged from 2.2° (gait; R² = 0.47) to 4.9° (sit-to-stand-to-sit; R² = 0.98), 0.6° (sitting; R² = 0.88) to 7.4° (gait; R² = 0.39), and 1.5° (forward bend; R² = 0.99) to 2.9° (sit-to-stand-to-sit; R² = 0.99) for motion about the X, Y, and Z axes, respectively. The magnitude of error observed for adjacent joint motion was lowest about the Z axis for all tasks. In conclusion, the accelerometer-based LCS offers an alternative method for computing pelvis and adjacent joint angles without the reliance on a visual line-of-sight. For motion about the X and Y axes, time-series data derived with the accelerometer-based method may be less representative of discrete events, particularly for gait and lunging tasks.

Effects of a liquid cooling vest on physiological and perceptual responses while wearing stab-resistant body armor in a hot environment

This study determines the effects of a liquid cooling vest (LCV) on physiological and perceptual responses while wearing stab-resistant body armor (SRBA). Ten healthy male volunteers wearing SRBA performed human trials with the LCV and without (control) in a hot environment (30 °C and 40% relative humidity). Physiological parameters and perceptual responses were recorded during the tests. The results indicated that the difference in the mean skin temperature and scapula skin temperature between the two conditions was up to 1.2 and 2.5 °C, respectively. The LCV did not significantly decrease the core temperature, heart rate, sweat loss, oxygen consumption, rating of perceived exertion and restriction of movement. However, a significant difference was observed between conditions in terms of evaporation efficiency and thermal sensation. Therefore, the LCV attenuated an increase in thermal sensation but did not mitigate physiological strain. This work can provide fundamental knowledge for high-performance personal cooling system development.