Musculoskeletal models have traditionally relied on measurements of segment kinematics and ground reaction forces and moments (GRF&Ms) from marked-based motion capture and floor-mounted force plates, which are typically limited to laboratory settings. Recent advances in inertial motion capture (IMC) as well as methods for predicting GRF&Ms have enabled the acquisition of these input data in the field. Therefore, this study evaluated the concurrent validity of a novel methodology for estimating the dynamic loading of the lumbar spine during manual materials handling based on a musculoskeletal model driven exclusively using IMC data and predicted GRF&Ms. Trunk kinematics, GRF&Ms, L4–L5 joint reaction forces (JRFs) and erector spinae muscle forces from 13 subjects performing various lifting and transferring tasks were compared to a model driven by simultaneously recorded skin-marker trajectories and force plate data. Moderate to excellent correlations and relatively low magnitude differences were found for the L4–L5 axial compression, erector spinae muscle and vertical ground reaction forces during symmetrical and asymmetrical lifting, but discrepancies were also identified between the models, particularly for the trunk kinematics and L4–L5 shear forces. Based on these results, the presented methodology can be applied for estimating the relative L4–L5 axial compression forces under dynamic conditions during manual materials handling in the field.

Physical inactivity is responsible for 7–10% of all premature deaths worldwide. Thus, valid, reliable and unobtrusive methods for monitoring activities of daily living (ADL) to predict total energy expenditure (TEE) is desired. Multiple methods exist to quantify TEE, but microelectromechanical systems (MEMSs) are the only method, which has shown promising results and are applicable for long-term monitoring in the field. However, no perfect method exists for predicting TEE on a daily basis. The present study evaluates TEE estimation based on a MEMS (Xsens Link system) taking gender and heart rate into account. Fifteen individuals performed seven ADL wearing the Xsens Link system, a heart rate belt and an oxygen mask. Multiple linear regression models were established for sedentary and dynamic activities and evaluated by leave-one-out cross-validation and compared with indirect calorimetry. The linear regression model showed better prediction for dynamic activities (adjusted R2 0.95±0.16) compared to sedentary activities (adjusted R2 0.61±0.19). The root-mean-square error for the TEE estimation ranged between 0.02 and 0.08 kJ/min/kg for the sedentary and dynamic models, respectively. The study showed a viable approach to predict TEE in ADL compared to previously published results. Further studies are warranted to reduce the number of sensors in the estimation of TEE.

Work related upper body musculoskeletal symptoms and disorders constitute a major problem for operators of heavy machinery. Steering input devices mediate risk factors of upper body musculoskeletal disorders. Little research has been conducted to compare the multiple commercially available steering input devices in a multi-faceted approach. The present study evaluated five commonly used steering input devices (conventional steering wheel, fast steering wheel, miniature steering wheel, first-order joystick and second-order joystick) in terms of muscle activity, upper body kinematics and steering performance during heavy machine simulator driving. Fifteen healthy males novice to operation of heavy machinery completed five laps on a simulated track with each steering input device. Results showed a generally lower muscle activity when using the joysticks. The conventional and fast steering wheel increased mean wrist and shoulder flexion/extension angles and participants spent more time in wrist flexion/extension angles corresponding to moderate and poor comfort levels. An increased elbow protonation angle was found for the three steering wheels compared to the joysticks. The conventional steering wheel showed slowest track completion time and was subjectively ranked worst. The first-order joystick was ranked highest but also showed the highest amount of steering reversal rates, posing a risk of increased repetitiveness. Overall, the second-order joystick is considered superior ergonomically compared to the other steering input devices evaluated. However, all evaluated steering input devices exceeded muscle activity and/or joint angle recommendations. Relevance to the industry: Compared to steering wheels, joystick steering showed reduced muscular activity and less awkward joint postures, suggesting a reduced risk of developing musculoskeletal disorders in the long term. However, the results warrant efforts to further develop joystick steering resulting in a reduction of exposure level beyond the existing solutions.

It is common sense that walking on sand poses challenges to postural control. However, there are no studies quantifying the kinematics of sand walking compared to other types of postural perturbations such as unstable shoes. The aim of the study was to investigate differences in walking kinematics during walking on solid ground, in unstable shoes and on unstable surfaces. Nineteen healthy young adults (23.5 ± 1.5 years) performed three different walking tasks: 1) walking at preferred speed while wearing regular shoes; 2) Walking at preferred speed wearing Masai Barefoot Technology shoes and 3) barefoot walking at preferred speed on a large sand grave. Full-body kinematics were recorded during all conditions using an inertial motion capture system. Basic gait parameters (walking speed, stride length and duration), relative vertical center-of-mass position (rvCOM), and ankle, knee and hip joint angles in the sagittal plane were compared across the tasks through statistical parametric mapping over the course of full walking cycles. Participants presented similar walking speed, as well as stride length and duration across different conditions (p > 0.05). However, walking on sand reduced the rvCOM (p < 0.05), while also requiring greater ankle plantarflexion during stance phase (p < 0.05), as well as greater knee and hip flexion during leg swing and initial contact when compared to the other conditions (p < 0.05). It was concluded that walking on sand substantially changes walking kinematics, and may cause greater postural instability than unstable shoes. Therefore, walking on sand can be an alternative to improve postural control in patients undergoing walking rehabilitation.

The objectives were 1) to design and produce two novel unpadded bicycle saddles with a wide/medium width and partial nose cutout; 2) to investigate the responses on pressure distribution and perceived discomfort in female cyclists. For comparison, a standard saddle was also tested. Nineteen female cyclists pedaled on an ergometer cycle for 20 min with each saddle in a counterbalanced order. A pressure mat measured saddle interface pressure. Discomfort ratings were collected using a visual analogue scale. Total mean saddle pressure remained similar across saddles. The wide saddle increased anterior and decreased posterior mean saddle pressure as compared with the standard (p<.002) and the medium saddle (p<.001). Significantly increased ischial tuberosity discomfort was found for the novel saddles (p<.001), while crotch discomfort was not significantly different between saddles. The medium width saddle appeared to be the best compromise since increased crotch discomfort was avoided and saddle pressures were redistributed. Such design may be suggested as an alternative to traditional saddles for women reporting discomfort in the perineal region.

Load carriage can be harmful for workers, and alternative interventions to reduce back pain while walking and carrying loads are necessary. Unstable shoes have been used to improve balance and reduce back pain, but it is unknown whether walking wearing unstable shoes while carrying loads anteriorly causes excessive trunk extensors muscle activation. The aim of this study was to investigate the effects of different shoe types and anterior load carriage on gait kinematics and lumbar electromyographic (EMG) activity. Fourteen adults that predominantly walk or stand during the work day were asked to walk with and without carrying 10% of body mass anteriorly while wearing regular walking shoes (REG) and unstable shoes (MBT). The effects of shoe type, load carriage, and shoe × load interactions on the longissimus thoracis (LT) and iliocostalis lumborum (IC) EMG, stride duration, and stride frequency were assessed. MBT shoes induced a significant increase in LT (44.4 ± 35%) and IC EMG (33.0 ± 32%, p < .005), while load carriage increased LT (58.5 ± 41%) and IC EMG (55.1 ± 32%, p < .001). No significant shoe × load interaction was found (p>.05). However, walking wearing MBT shoes while carrying loads induced a 46 ± 40% higher EMG activity compared to walking wearing MBT shoes without load carriage. No effects of shoes or load carriage were found on stride duration and stride frequency. It was concluded that walking wearing MBT shoes and carrying 10% of total body mass induced greater activation of trunk extensors muscle compared to these factors in isolation, such a combination may not influence gait patterns.