Nico J. Delleman

Effects of field-of-view restrictions on speed and accuracy of manoeuvring

Effects of field-of-view restrictions on the speed and accuracy of participants performing a real-world manoeuvring task through an obstacled environment were investigated. Although field-of-view restrictions are known to affect human behaviour and to degrade performance for a range of different tasks, the relationship between human manoeuvring performance and field-of-view size is not known. This knowledge is essential to evaluate a trade-off between human performance, cost, and ergonomic aspects of field-of-view limiting devises like head-mounted displays and night vision goggles which are frequently deployed for tasks involving human motion through environments with obstacles. In this study the speed and accuracy of movement were measured in 15 participants (8 men, 7 women, 22.9 ± 2.8 yr. of age) traversing a course formed by three wall segments for different field-of-view restrictions. Analysis showed speed decreased linearly with decreasing field-of-view extent, while accuracy was consistently reduced for all restricted field-of-view conditions. Present results may be used to evaluate cost and performance trade-offs for field-of-view restricting devices deployed to perform time-limited human-locomotion tasks in complex structured environments, such as night-vision goggles and head-mounted displays.

International standards on working postures and movements ISO 11226 and EN 1005-4

Standards organizations have given considerable attention to the problem of work-related musculoskeletal disorders. The publication of international standards for evaluating working postures and movements, ISO 11226 in 2000 and EN 1005-4 in 2005, may be considered as a support for those involved in preventing and controlling these disorders. The first one is a tool for evaluation of existing work situations, whereas the latter one is a tool for evaluation during a design/engineering process. Key publications and considerations that led to the content of the standards are presented, followed by examples of application.

Effect of ship motion on spinal loading during manual lifting

This study investigated the effects of ship motion on peak spinal loading during lifting. All measurements were done on a ship at sea. In 1-min trials, which were repeated over a wide range of sailing conditions, subjects lifted an 18 kg box five times. Ship motion, whole body kinematics, ground reaction forces and electromyography were measured and the effect of ship motion on peak spinal moments and compression forces was investigated. To investigate whether people time their lifts in order to reduce the effect of ship motion on back loading, trials were performed at a free and at a constrained (lifting every 10s) work pace. With increase of the (local) vertical ship acceleration, increased moments and compression forces were found. Furthermore, lifting at a free work pace did not result in smaller effects of ship motion on spinal moments and compression forces than working at a constrained work pace.

The effect of ship accelerations on three-dimensional low back loading during lifting and pulling activities

Manual materials handling on a moving platform, like a ship, might be a risk factor for the development of lowback pain due to the in.uence of accelerations on lowback loading. In the current simulation study, 3-D accelerations, measured on a frigate were applied to the kinematics of symmetrical and asymmetrical lifting movements and to a pulling task that had been performed under stable conditions. The aim was to find out to what extent low back loading is increased when the task execution is not adapted to the ship accelerations. Unfavorable timing, analyzed using the 99th percentile of predicted lowback moments, resulted in only a moderate (up to 15%) increase of extending and total lowback moments, and in a substantial increase of the twisting moment (up to 67%) during asymmetrical lifting. Moments in the pulling task were low and were relatively unaffected by ship accelerations, but adaptation of the movement pattern to prevent falling would be needed more often than during lifting. It furthermore appeared that a substantial reduction of lowback loading by favorable timing is not a realistic option. Designing tasks in such a way that they are located midship would reduce the 99th percentile of predicted low back moments. During lifting, orienting the task in such a way that the feet are pointing sideward relative to the ship reduces the predicted peak twisting moment at the low back compared to pointing the feet forward or backward.

Effects of field-of-view restriction on manoeuvring in a 3-D environment

Field-of-view (FOV) restrictions are known to affect human behaviour and to degrade performance for a range of different tasks. However, the relationship between human locomotion performance in complex environments and FOV size is currently not fully known. This paper examined the effects of FOV restrictions on the performance of participants manoeuvring through an obstacle course with horizontal and vertical barriers. All FOV restrictions tested (the horizontal FOV was either 30°, 75° or 120°, while the vertical FOV was always 48°) significantly reduced performance compared to the unrestricted condition. Both the time and the number of footsteps needed to traverse the entire obstacle course increased with a decreasing FOV size. The relationship between FOV restriction and manoeuvring performance that was determined can be used to formulate requirements for FOV restricting devices that are deployed to perform time-limited human locomotion tasks in complex structured environments, such as night-vision goggles and head-mounted displays used in training and entertainment systems.

Predicting Marching Capacity While Carrying Extremely Heavy Loads

The objective of this study was to establish the best prediction for endurance time of combat soldiers marching with extremely heavy loads. It was hypothesized that loads relative to individual characteristics (% maximal load carry capacity [MLCC], % body mass, % lean body mass) would better predict endurance time than load itself. Twenty-three male combat soldiers participated. MLCC was determined by increasing the load by 7.5 kg every 4 minutes until exhaustion. The marching velocity and gradient were 3 km.h(-1) and 5%, respectively. Endurance time was determined carrying 70, 80, and 90% of MLCC. MLCC was on average 102.6 kg +/- 11.6. Load expressed as % MLCC was the best predictor for endurance time (R2 = 0.45). Load expressed as % body mass, as % lean body mass, and absolute load predicted endurance time less well (R2 = 0.30, R2 = 0.24, and R2 = 0.23, respectively). On the basis of these results, it is recommended to assess the MLCC of individual combat soldiers.

Effects of field of view on human locomotion

Field of view (FOV) restrictions are known to impair human performance for a range of different tasks. However, the effects of FOV restrictions on human locomotion through a complex environment are still not clear. This is particularly important for the development and deployment of FOV restricting devices like Head Mounted Displays (HMDs), which generally have FOVs that are much smaller than the unrestricted FOV. We investigated the effects of both horizontal and vertical FOV restrictions on the walking speed and head movements of participants manoeuvring through complex 3D obstacle courses. All FOV restrictions tested significantly increased the time needed to complete the courses, compared to the unrestricted condition. The time needed to traverse a course was significantly longer for a vertical FOV of 18° than for a vertical FOV of 48°. For a fixed vertical FOV size, the traversal time was constant for horizontal FOV sizes ranging between 75° and 180°, and increased significantly for the 30° horizontal FOV condition. The implications of the current findings for the development of devices with FOV restrictions (like HMDs) are discussed.

Prediction of Musculoskeletal Discomfort in a Pick and Place Task (A pilot study)

A pilot study was conducted regarding the effects of working posture, handling frequency, and task duration on musculoskeletal discomfort. Participants rated their discomfort perceived while performing a repetitive task at 8 different combinations of manipulations. Pauses between the work periods lasted 15 min. Discomfort was rated according to Borgs category-ratio scale CR-10 and postures were recorded by an optoelectronic movement registration system. From linear multiple regression analysis equations for predicting discomfort at various body regions were obtained. Coefficients of determination especially point to trunk inclination and handling frequency as major determinants of musculoskeletal discomfort.

Effects of horizontal field-of-view restriction on manoeuvring performance through complex structured environments

Field-of-view (FOV) restrictions are known to affect human behaviour and to degrade performance for a range of different tasks. A proposed cause for this performance impairment is the predominant activation of the ventral cortical stream as compared to the dorsal stream. This may compromise the ability to control heading as well as degrade the processing of spatial information [Patterson et al. 2006]. Furthermore, the peripheral visual field is important in maintaining postural equilibrium [Turano et al. 1993]. These are all significant factors when manoeuvring through complex structured environments. We discuss here two experiments investigating the influence of horizontal FOV-restriction on manoeuvring performance through real-world structured environments. The results can help determine requirements for the selection and development of FOV limiting devices such as Head-Mounted Displays (HMDs).

Approach strategy and working posture in manual hand tool operation.

The strategy for approaching a manual work position is an important reference for describing a goal-directed task. However, knowledge on this aspect of human behavior is scarce. The objectives of this study are twofold: (1) to describe and understand the strategy people tend to adopt for approaching a manual work position from different directions when their initial standing position is three meters away, and (2) to describe the working posture they tend to adopt when operating a pistol-grip hand tool at different heights. An experiment involving eight participants was conducted to measure the whole-body position and orientation when approaching a work position from five directions. The working posture adopted when operating a pistol-grip hand tool at six working heights was examined. The results indicate that the final whole-body position and orientation (while performing the operation) was affected significantly by the approach direction. A linear relationship between the approach direction and the final whole-body orientation was obtained. The participants adopted a strategy combining the work efficiency and comfort strategies. They deviated from the least-distance (straight line) walking path and re-oriented their whole body for the operation when approaching the work position. The working posture was significantly affected by the working height. The working postures at six working heights were established. The participants adopted a standing posture when the working height was between eye and hip height, and a stooping or squatting posture when operating at knee and ankle height. The results of this study can be used to enhance digital human modeling motion generated for human movement simulation.