Boyi Hu

The changes of lumbar muscle flexion–relaxation response due to laterally slanted ground surfaces

Lifting tasks performed on uneven ground surfaces are common in outdoor industries. Previous studies have demonstrated that lifting tasks performed on laterally slanted ground surfaces influence lumbar muscle activation and trunk kinematics. In this study, the effect of laterally slanted ground surfaces on the lumbar muscle flexion–relaxation responses was investigated. Fourteen participants performed sagittal plane, trunk flexion–extension tasks on three laterally slanted ground surfaces (0° (flat ground), 15° and 30°), while lumbar muscle activities and trunk kinematics were recorded. Results showed that flexion–relaxation occurred up to 6.2° earlier among ipsilateral lumbar muscles with an increase in laterally slanted ground angle; however, the contralateral side was not affected as much. Our findings suggest that uneven ground alters the lumbar tissue load-sharing mechanism and creates unbalanced lumbar muscle activity, which may increase the risk of low back pain with repeated exposure to lifting on variable surfaces. Practitioner Summary: Uneven ground surfaces are ubiquitous in agriculture, construction, fishing and other outdoor industries. A better understanding of the effects of laterally slanted ground surfaces on the interaction between passive and active lumbar tissues during lifting tasks could provide valuable knowledge in the design of preventive strategies for low back injuries.

The influence of lumbar extensor muscle fatigue on lumbar–pelvic coordination during weightlifting

Lumbar muscle fatigue is a potential risk factor for the development of low back pain. In this study, we investigated the influence of lumbar extensor muscle fatigue on lumbar–pelvic coordination patterns during weightlifting. Each of the 15 male subjects performed five repetitions of weightlifting tasks both before and after a lumbar extensor muscle fatiguing protocol. Lumbar muscle electromyography was collected to assess fatigue. Trunk kinematics was recorded to calculate lumbar–pelvic continuous relative phase (CRP) and CRP variability. Results showed that fatigue significantly reduced the average lumbar–pelvic CRP value (from 0.33 to 0.29 rad) during weightlifting. The average CRP variability reduced from 0.17 to 0.15 rad, yet this change ws statistically not significant. Further analyses also discovered elevated spinal loading during weightlifting after the development of lumbar extensor muscle fatigue. Our results suggest that frequently experienced lumbar extensor muscle fatigue should be avoided in an occupational environment. Practitioner Summary: Lumbar extensor muscle fatigue generates more in-phase lumbar–pelvic coordination patterns and elevated spinal loading during lifting. Such increase in spinal loading may indicate higher risk of back injury. Our results suggest that frequently experienced lumbar muscle fatigue should be avoided to reduce the risk of LBP.

The Changes of Trunk Motion Rhythm and Spinal Loading During Trunk Flexion and Extension Motions Caused by Lumbar Muscle Fatigue

Previous studies indicated that lumbar extensor muscle fatigue could potentially affect lumbar–pelvic rhythm and influence spinal loading during trunk motions. In this study, the effects of lumbar extensor muscle fatigue on the normalized lumbar–pelvic rotation rhythm and the associated L5/S1 joint loading during weight lifting and lowering tasks were investigated. Thirteen volunteers performed lifting and lowering of a 20-lbs box both before and after lumbar extensor muscle fatigue, which was generated through a static weight holding task. The normalized lumbar–pelvic motion ratio (L/P ratio) and the external moment on the L5/S1 joint were calculated and compared. Results showed that subjects demonstrated significantly larger normalized L/P ratios during both weight lifting and lowering tasks with the influence of fatigue. In addition, although the spinal loadings remain unchanged at the beginning and ending of both lifting and lowering motions, significantly larger L5/S1 joint moments were observed during both motions after fatigue. Such changes indicate potentially elevated risk of back injury. In a clinical setting, the current results demonstrated that lumbar muscle fatigue could cause transient changes in lumbar–pelvic motion rhythm. Therefore, lumbar muscle fatigue must be avoided when using lumbar–pelvic motion rhythms for patient diagnosis or rehabilitation assessment.

The influence of hand load on lumbar-pelvic coordination during lifting task

Manual material handling (MMH) tasks such as weight lifting are very common in many industries. The effect of hand load on lumbar-pelvic continuous relative phase (CRP) coordination during lifting was investigated in this study. Twelve male subjects performed sagittal symmetric lifting tasks with or without load in hand; meanwhile lumbar kinematics data were recorded. Results of the current study demonstrated a significant difference of lumbar-pelvic coordination between the two conditions. Subjects tended to show more in-phase CRP pattern when lifting a load. Also, when lifting a load subjects’ lumbar-pelvic motion pattern made their torso generated larger loading on the L5/S1 joint. The findings of this study can be used to better understand how hand load influences lifting biomechanics.

The influences of foot placement on lumbopelvic rhythm during trunk flexion motion

Different standing postures could potentially influence trunk biomechanics during task performance. The current study investigated how foot placement, especially stance width and foot angle influenced lumbopelvic rhythm during sagittal trunk flexion motion. Ten participants performed pace controlled sagittally symmetric trunk flexion motions while maintaining three different stance widths and two different foot angles. The results showed the narrower stance and angled foot placement conditions generated more in-phase lumbopelvic coordination patterns during trunk flexion motions, possibly due to the reduced base of support and the associated postural stability. Findings of this study provided important information regarding the effects of foot placement on postural control and trunk biomechanics during trunk bending motions; these results suggested that foot placement could alter the motion patterns of spinal segments.

Changes of Lumbar Muscle Flexion Relaxation Phenomenon When Standing on Unilaterally Elevated Ground

Occupational tasks performed on uneven ground surfaces are common in agriculture and construction industries. The influence of unilaterally elevated ground surface on lumbar muscle flexion relaxation phenomenon (FRP) during trunk flexion and extension motion has been investigated in the current study. Ten subjects performed trunk flexion and extension motion on flat ground and two unilaterally elevated ground conditions while lumbar muscle EMG and trunk kinematics data were recorded. Results of this study demonstrated clear difference in bilateral lumbar muscle FRP under elevated ground conditions. The current finding can be used to better understand uneven ground surfaces as a risk factor for the development of low back pain.

Machine learning algorithms based on signals from a single wearable inertial sensor can detect surface- and age-related differences in walking.

The aim of this study was to investigate if a machine learning algorithm utilizing triaxial accelerometer, gyroscope, and magnetometer data from an inertial motion unit (IMU) could detect surface- and age-related differences in walking. Seventeen older (71.5 ± 4.2 years) and eighteen young (27.0 ± 4.7 years) healthy adults walked over flat and uneven brick surfaces wearing an inertial measurement unit (IMU) over the L5 vertebra. IMU data were binned into smaller data segments using 4-s sliding windows with 1-s step lengths. Ninety percent of the data were used as training inputs and the remaining ten percent were saved for testing. A deep learning network with long short-term memory units was used for training (fully supervised), prediction, and implementation. Four models were trained using the following inputs: all nine channels from every sensor in the IMU (fully trained model), accelerometer signals alone, gyroscope signals alone, and magnetometer signals alone. The fully trained models for surface and age outperformed all other models (area under the receiver operator curve, AUC = 0.97 and 0.96, respectively; p ≤ .045). The fully trained models for surface and age had high accuracy (96.3, 94.7%), precision (96.4, 95.2%), recall (96.3, 94.7%), and f1-score (96.3, 94.6%). These results demonstrate that processing the signals of a single IMU device with machine-learning algorithms enables the detection of surface conditions and age-group status from an individuals walking behavior which, with further learning, may be utilized to facilitate identifying and intervening on fall risk.

The changes of lumbar muscle flexion-relaxation phenomenon due to antero-posteriorly slanted ground surfaces

Abstract Uneven ground surface is a common occupational injury risk factor in industries such as agriculture, fishing, transportation and construction. Studies have shown that antero-posteriorly slanted ground surfaces could reduce spinal stability and increase the risk of falling. In this study, the influence of antero-posteriorly slanted ground surfaces on lumbar flexion-relaxation responses was investigated. Fourteen healthy participants performed sagittally symmetric and asymmetric trunk bending motions on one flat and two antero-posteriorly slanted surfaces (−15° (uphill facing) and 15° (downhill facing)), while lumbar muscle electromyography and trunk kinematics were recorded. Results showed that standing on a downhill facing slanted surface delays the onset of lumbar muscle flexion-relaxation phenomenon (FRP), while standing on an uphill facing ground causes lumbar muscle FRP to occur earlier. In addition, compared to symmetric bending, when performing asymmetric bending, FRP occurred earlier on the contralateral side of lumbar muscles and significantly smaller maximum lumbar flexion and trunk inclination angles were observed. Practitioner Summary: Uneven ground surface is a common risk factor among a number of industries. In this study, we investigated the influence of antero-posteriorly slanted ground surface on trunk biomechanics during trunk bending. Results showed the slanted surface alters the lumbar tissue load-sharing mechanism in both sagittally symmetric and asymmetric bending.

Effects of Touch Screen Interface Parameters on User Task Performance

The influence of different touch screen interface design features on user experience and operators’ task performance was investigated in the current study. Eight participants performed different tasks on a touchscreen monitor with varied interface settings while their performance was recorded and compared. Results demonstrated that an oversized desktop touchscreen monitor could generate negative impacts on users’ performance. Smaller icon size also decreased task performance by increasing total response time. In addition, icon color also influenced users’ performance. Results of the current study provide useful data for new approaches to design improvements which will enhance human performance and users’ experience.

Effects of Uneven Ground Surface on Human Balance

The effect of anteroposteriorly slanted ground surface on human posture control at fully flexed trunk postures was investigated in this study. Custom made wooden apparatus were used to simulate slanted ground surfaces, the slanted were set at -15, 0 and 15 degrees respectively. The flat ground condition was included in the study as a control. Fourteen healthy male subjects were asked to maintain in fully flexed trunk posture while standing on different ground surfaces. The segmental sway motion of C7, T12 and S1 spinal vertebrae in the anteroposterior (AP) and mediolateral (ML) directions were recorded. Results showed that when standing on an anteroposteriorly slanted ground surface and facing downhill (i.e. -15 degree condition) subjects consistently demonstrated the highest sway speeds and reported the highest subjective rating of instability. Therefore, we concluded that, when standing on an anteroposteriorly slanted ground surface in a fully flexed trunk posture facing downhill may result in much higher risk of falling in comparison to facing the opposite direction.