Rong Huangfu

Characterizing exposure to physical risk factors among reforestation hand planters in the Southeastern United States

Low back and neck/shoulder pain are commonly reported among reforestation hand planters. While some studies have documented the intensive cardiovascular demands of hand planting, limited information is available regarding exposures to physical risk factors associated with the development of musculoskeletal disorders (MSDs) among hand planters. This study used surface electromyography (EMG) and inertial measurement units (IMUs) to characterize the muscle activation patterns, upper arm and trunk postures, movement velocities, and physical activity (PA) of fourteen Southeastern reforestation hand planters over one work shift. Results indicated that hand planters are exposed to physical risk factors such as extreme trunk postures (32.5% of time spent in ≥45° trunk flexion) and high effort muscle exertions (e.g., mean root-mean-square right upper trapezius amplitude of 54.1% reference voluntary exertion) that may place them at increased risk for developing MSDs. The findings indicate a need for continued field-based research among hand planters to identify and/or develop maximally effective interventions.

Evaluating the Linear Integration Method of Estimating Cumulative Loading Using an Eccentric Exercise

The ability to quantify cumulative exposure is critically in understanding dose-response relationship in the development of work-related musculoskeletal disorders. Different integration methods have been used in estimating cumulative loading (force or torque). The general objective of cumulative loading integration methods has been to sum the loading exposure for each individual task, calculate by multiplying the magnitude of the task loading times the task duration, and develop an “area under the curve”. An assumption of this linear integration model is that short time exposure to high forces will result in a similar level of damage as relatively long-time exposure to low forces. In this study, three loading groups of eccentric exercise with the same “area under the curve” were performed by thirty participants (ten in each group). Relaxed elbow angle and maximum isometric voluntary contractions (MIVC) were collected before, immediately after, and 2, 4, 8 days after the exercise. The relaxed elbow angle and the changes in MIVC were significantly impacted by the loading group. This result suggests that the linear integration method of estimating cumulative loading may underestimate the impact of high force loading in terms of cumulative muscle damage.

Lumbar Muscle Fatigue Analysis Using Sorensen Test with Different Upper Body Offload Conditions

The Sorensen test has been widely used in assessing the isometric endurance of trunk muscles. In this study, a modified Sorensen test was performed using four different upper body offload conditions (0%, 25% 50% and 75%) and surface EMG (sEMG) was used to determine fatigue characteristics in lumbar muscles. Results showed that the offloading of the upper body has a statistically significant impact on the slope of the EMG median frequency, which is representative of lumbar muscle fatigue responses. The first 25% offloading significantly decreased the fatigue response in the lumbar region. In addition, the 25% offload condition was significantly different from the 75% offload condition. However, the slopes of 25% and 50% offload conditions are not statistically different from each other and same for 50% and 75% offload conditions.

Use of Varied Definitions of Repetition with the Distal Upper Extremity Tool (DUET)

Defining what constitutes a repetition in performance of a task involving exertions of the upper extremity can be difficult due to highly varied activities. In this paper, we examine three different definitions of repetition with the use of the Distal Upper Extremity Tool (DUET). These definitions include Grips Alone (manipulation of an object by the hands), Reps Alone (wrist deviations), and Grips + Reps (manipulations plus deviations). Validation of the DUET tool was performed against an existing cross-sectional epidemiology study for all three definitions. The log of the DUET Cumulative Damage (CD) measure demonstrated strong and consistent associations with five separate distal upper extremity outcomes using each of these definitions of repetition when controlled for covariates including site, gender, age, and BMI (with significant odds ratios ranging from 1.20 – 2.10). Results suggest that DUET may allow for flexibility in the definition of “repetition” and still successfully identify hazardous jobs.

Validation of the Lifting Fatigue Failure Tool (LiFFT)

Manual material handling is common in industry and has demonstrated a strong association with the development of low back disorders (LBDs). Several risk assessment tools exist in the literature to assess acceptable lifting limits, and/or the development of improved design of manual lifting tasks. However, recent evidence has strongly suggested that LBDs (and other MSDs) may the result of a process of mechanical fatigue failure. Prior tools have not used fatigue failure methods to assess risk, which may be beneficial is these disorders are indeed the result of such a process. The purpose of this paper is to describe a new risk assessment tool for manual lifting (LiFFT) and to provide validation of this tool using two existing epidemiological databases. Results demonstrate that the LiFFT cumulative damage measure is significantly associated with low back outcomes in both epidemiological studies.

Assessment of Job Rotation Effects for Lifting Jobs Using Fatigue Failure Analysis

Job rotation is a common method employed by industry to reduce the risk of musculoskeletal disorders (MSDs). However, the efficacy of this technique has been open to question and methods of quantifying the effects of job rotation strategies have been scarce. However, recent evidence has suggested that MSDs may be the result of a fatigue failure process, and new risk assessment tools have been developed that have the capability to assess the effects of various job rotation strategies on MSD risk. The current analysis uses the Lifting Fatigue Failure Tool (LiFFT) to assess cumulative loading for a simulated job rotation scheme. Results of this analysis suggest that attempting to “balance” a high risk, medium risk, and low risk lifting job ends up creating three jobs that are all high risk. Rotation may somewhat reduce the risk associated with the worst job, but this will be accompanied by a steep increase in risk faced by all other workers in the rotation pool.

Evaluating the Effectiveness of Estimating Cumulative Loading Using Linear Integration Method

Exposure to cumulative loading is a significant risk factor in the development of musculoskeletal disorders (MSD). To better understand the dose-response relationship, it is critically to quantify the cumulative exposure. Different integration methods have been used in estimating cumulative loading (force or torque). The general objective of the integration methods has been to sum the independently calculated task exposure. Each task was calculated by multiplying the magnitude of the task loading times the task duration which is the “area under the loading curve”. An assumption of this linear integration model is that long-time exposure to low forces will result in a similar level of damage as relatively short time exposure to high forces. To evaluate the effectiveness of this model, three loading groups of eccentric exercise with the same “area under the loading curve” were performed by thirty participants (ten in each group). Maximum isometric voluntary contractions (MIVC) and relaxed elbow angle (REA) were collected before, immediately after, and 2, 4, 8 days after the exercise. The REA and MIVC changes after the eccentric exercise were significantly impacted by the loading group. It suggests that estimating cumulative loading using linear integration method may underestimate the impact of high force loading in terms of cumulative muscle damage.

Validation of A Fatigue Failure-based Risk Assessment Tool For Distal Upper Extremity MSDs

This paper presents a new practitioner-friendly distal upper extremity tool (DUET) based on fatigue failure theory. The tool requires only assessment of force exertion (using the OMNI-RES scale) and the number of repetitions performed to derive DUE risk. Validation of this tool was performed against six separate DUE outcomes from an epidemiological database involving data obtained from 1,022 participants across 738 jobs from several automotive manufacturing plants. The DUET Cumulative Damage (CD) measure explained between 79-95% of the deviance for the six DUE outcomes in logistic regression analyses.

Validation of the LiFFT Risk Assessment Tool and Guidance on Its Use

The purpose of this paper is to describe a new risk assessment tool for manual lifting (LiFFT), to demonstrate the strong association between LiFFT’s cumulative damage metric with low back outcomes, and to provide recommendations for use in a variety of settings.

Job Rotation as a Technique for the Control of MSDs: A Fatigue Failure Perspective

Job rotation is a common method employed by industry to reduce the risk of musculoskeletal disorders (MSDs). However, the efficacy of this technique has been open to question and methods of quantifying job rotation strategies have been scarce. The current analysis uses the LiFFT low back risk assessment tool to assess cumulative loading for a job rotation scheme. Results of this analysis suggest that attempting to “balance” a high risk, medium risk, and low risk lifting job ends up creating three jobs that are all high risk.