The use of riding lawn equipment (RLE) is related to a significant number of accidents every year. To provide basis for product design and enhance user performance and safety, a usability and performance assessment of modern riding lawn-mowing tractor designs and features was conducted in a real-world test environment. Five current commercially available RLEs were tested with response measures including task performance time and accuracy, physiological workload, system usability scores (SUS), and subjective rankings of RLE models. This data was used to identify sensitivity of responses to variations in RLE design features and functionality. The data was also used to assess the validity of new tractor design standard conformance tool, the RLEval methodology. This tool made comprehensive evaluation of RLE models compliance with over 70 specific design standards and was applied by human factors experts. Experiment results revealed sensitivity of all response measures to design differences among the five RLE models, except the objective workload measures. Response measures including task performance, SUSs and subjective rankings showed partial agreement with the RLEval scores. In general, the study results demonstrated a comprehensive experimental methodology for usability and performance evaluations of RLEs as well as merit of using the RLEval as preliminary method to compare design features. Some aspects of the usability experimentation and the RLEval method appear to be complementary.

The US Bureau of Labor Statistics (BLS) reports that amongst private sector industries, the Transportation and Warehousing sector has the highest incidence rate of musculoskeletal disorders. In 2014, laborers and freight, stock and material movers had one of the highest incidence rates of overexertion injuries. Of all non‐fatal lost time injuries reported, lower extremities were the second most frequently injured part of the body [1].

Riding lawn equipment (RLE) is a common household appliance. Methods are needed for systematic evaluation of RLEs in order to promote usability and safety for users. Current RLE research and guidelines were used as a basis for developing a new tool for scoring modern RLEs in terms of a range of design features. In this paper, we outline the development and application of the riding lawn equipment evaluation tool (RLEval) for measuring and reporting RLE conformance with existing ISO and ANSI safety, usability, and functionality standards. Additionally, recommendations are made for RLE guideline enhancements and guideline literature limitations are identified. Preliminary evaluations of multiple RLE models were conducted to assess the utility and reliability of the RLEval and to compare tractors.

In a survey of 341 workers, we have found lower extremity musculoskeletal symptoms to be prevalent in distribution center employees working in material handling jobs. This study was a cross-sectional field study aimed at developing risk models showing associations between tibial acceleration and lower extremity musculoskeletal disorder symptoms. One hundred thirty two participants volunteered to wear uni-axial accelerometers that quantified their bilateral tibial acceleration exposures during two hours of normal work activities and also completed a questionnaire assessing individual factors and their experience with lower extremity musculoskeletal symptoms. The questionnaire and accelerometer data were used to develop logistic regression models exploring the relationships between the likelihood of self-reported lower extremity symptoms in the hip/thigh, knee, and ankles/feet and relevant biomechanical and individual exposure variables. An outcome score was created by multiplying the symptom frequency score by the symptom severity score by the therapy score for both the knees and the ankles/feet regions. Only the symptom frequency and severity scores were multiplied to create the hip/thigh outcome score. Multiple logistic regression models were used to predict the probability of being symptomatic based on the accelerometer, work exposure, and individual characteristics predictor variables. Table 1 shows the sensitivity of the models predicting symptoms in the hip/thighs, knees, and ankles/feet and the contributing predictor variables.

This study investigated biomechanical effects of different leg folding/unfolding mechanisms used for loading/unloading two powered cots (Cots A and B) into and from a simulated ambulance. Sixteen experienced emergency medical service (EMS) workers loaded and unloaded cots with weights of 45, 68 and 91 kg placed on the cots to simulate patients. Peak back and shoulder/arm muscle activity was reduced 52-87% when using Cot A in comparison to Cot B. Peak ground reaction force (PGRF) was reduced by 74% with Cot A. Adding weight resulted in increased muscle activity and PGRF when using Cot B, but had little effect when using Cot A. Task time was longer with Cot A, though was not perceived unfavourably by participants. This study confirmed that it is possible to substantially reduce physical stress imposed on EMS workers when loading and unloading a cot to and from an ambulance through improvements in cot design.PRACTITIONER SUMMARY:This study compared two powered ambulance cots, one that lifts/lowers the front and rear wheels independently and one that lifts/lowers the four wheels simultaneously during ambulance loading and unloading. Measured muscle activity, ground reaction forces and operator perceptions support using cot designs that lift/lower the front and rear wheels independently.

Lower extremity musculoskeletal disorders and injuries affect a number of people in occupational settings. In many occupations, such as manual material handling jobs at distribution centers, there is exposure to prolonged standing, excessive walking on hard surfaces or uneven surfaces, stepping up or down between work surfaces, and there is vibration exposure. Quantifying these occupational exposures and their relationship to injury is necessary to determine thresholds that can be used to identify safe versus unsafe exposures levels for the lower extremities. To understand the force vectors generated at heel strike during walking, previous studies have used transient impulse forces on the tibia, also known as tibial shock [1,2].

An experiment was conducted in order to examine the effect of differences in the design of two powered ambulance cots on operators. Experienced EMS workers performed two common tasks, loading and unloading the cots from a simulated ambulance bed. Dependent measures included muscle activity (trunk, shoulder, and arm muscles) and subjective perceptions. Independent variables were cot (Cot R and Cot Y), and weight on the cot (100, 150, and 200 lbs., to simulate patients of different weights). Muscle activity was found to be significantly lower when using Cot R, for both tasks, in comparison to Cot Y. Subjective preferences were mixed, with many subjects preferring the handle design of Cot Y, while preferring Cot R overall. This study showed that it is possible to substantially reduce the physical stress imposed on operators when loading and unloading a cot to and from an ambulance through improvements in cot design.

Effects of ambulance cot design features (handle design and leg folding mechanism) were evaluated. Experienced ambulance workers performed tasks simulating loading and unloading a cot to and from an ambulance, and a cot raising task. Muscle activity, ratings of perceived exertion, and performance style were significantly affected by cot condition (p < 0.05). Erector Spinae activity was significantly less when using Cot-2's stretcher-style handles. Shoulder muscle activity was significantly less when using Cot-2's loop handle. During loading and unloading, operators allowed the cot to support its own weight most often with Cot-2's stretcher-style handles. Preference for Cot-2 (either handles) over Cot-1 (with loop handle) was consistent across tasks. Handle effects were influenced by operator stature; taller participants received more benefit from Cot-2's stretcher-style handles; shoulder muscles’ demands were greater for shorter participants due to handle location. Providing handle options and automatic leg folding/unfolding operation can reduce cot operator's effort and physical strain. Practitioner Summary: Paramedics frequently incur musculoskeletal injuries associated with patient-handling tasks. A controlled experiment was conducted to assess effects of ambulance cot design features on physical stress of operators, as seen through muscle activity and operator's perceptions. Differences between cots were found, signalling that intentional design can reduce operator's physical stress.

The objective of this study was to investigate potential associations between an individual's psychophysical maximum acceptable force (MAF) during pushing tasks and biomechanical tissue loads within the lumbar spine. Ten subjects (eight males, two females) pushed a cart with an unknown weight at one push every two minute for a distance of 3.9 m. Two independent variables were investigated, cart control and handle orientation while evaluating their association with the MAF. Dependent variables of hand force and tissue loads for each MAF determination and preceding push trial were assessed using a validated, electromyography-assisted biomechanical model that calculated spinal load distribution throughout the lumbar spine. Results showed no association between spinal loads and the MAF. Only hand forces were associated with the MAF. Therefore, MAFs may be dependent upon tactile sensations from the hands, not the loads on the spine and thus may be unrelated to risk of low back injury. Practitioner Summary: Pushing tasks have become common in manual materials handling (MMH) and these tasks impose different tissue loads compared to lifting tasks. Industry has commonly used the psychophysical tables for job assent and decision of MMH tasks. However, due to the biomechanical complexity of pushing tasks, psychophysics may be misinterpreting risk.