Jeremy Rickards

Computer terminal work and the benefit of microbreaks

Microbreaks are scheduled rest breaks taken to prevent the onset or progression of cumulative trauma disorders in the computerized workstation environment. The authors examined the benefit of microbreaks by investigating myoelectric signal (MES) behavior, perceived discomfort, and worker productivity while individuals performed their usual keying work. Participants were randomly assigned to one of three experimental groups. Each participant provided data from working sessions where they took no breaks, and from working sessions where they took breaks according to their group assignment: microbreaks at their own discretion (control), microbreaks at 20 min intervals, and microbreaks at 40 min intervals. Four main muscle areas were studied: the cervical extensors, the lumbar erector spinae, the upper trapezius/supraspinatus, and the wrist and finger extensors. The authors have previously shown that when computer workers remained seated at their workstation, the muscles performing sustained postural contractions displayed a cyclic trend in the mean frequency (MNF) of the MES (McLean et al., J. Electrophysiol. Kinesiol. 10 (1) (2000) 33). The data provided evidence (p < 0.05) that all microbreak protocols were associated with a higher frequency of MNF cycling at the wrist extensors, at the neck when microbreaks were taken by the control and 40 min protocol groups, and at the back when breaks were taken by the 20 and 40 min protocol groups. No significant change in the frequency of MNF cycling was noted at the shoulder. It was determined (p < 0.05) that microbreaks had a positive effect on reducing discomfort in all areas studied during computer terminal work, particularly when breaks were taken at 20 min intervals. Finally, microbreaks showed no evidence of a detrimental effect on worker productivity. The underlying cause of MNF cycling, and its relationship to the development of discomfort or cumulative trauma disorders remains to be determined.

Bilateral isokinetic training reduces the bilateral leg strength deficit for both old and young adults

The bilateral limb deficit (BLD) describes the difference in maximal or near-maximal force generating capacity of muscles when they are contracted alone and in combination with the contralateral muscles. This study examined the effects of a 6-week (three times per week) bilateral leg strength training programme on BLD in younger and older adults. Data were collected from 33 subjects during slow (45°/s) isokinetic knee extensions and flexions before and after the training programme. After training, the BLD was reduced for extension (73.3–86.9%; P<0.001) but not for flexion (67.5–71.2%; P=0.13) regardless of age and gender. This study suggests that difficulty in recruiting all muscle units during a task involving bilateral activation can be improved by training, although such an effect appears to depend on the muscle group appreciated.

Effect of stiffness and movement speed on selected dynamic torque characteristics of hydraulic-actuation joystick controls for heavy vehicles

The purpose of this work was to quantify the effects of joystick stiffness and movement speed on the dynamic torque characteristics of hydraulic-actuation joystick controls, as found in off-road vehicles, as one of the initial steps towards the development of a joystick design protocol. Using a previously developed mathematical model in which a hydraulic-actuation joystick is assumed to rotate about two axes where the rotation origin is a universal joint, the dynamic torque characteristics incurred by an operator were predicted. Utilizing a laboratory mock-up of an excavator cab environment, three actuation torque characteristics (peak torque, angular impulse and deceleration at the hard endpoint) were quantified for nine unskilled joystick operators during the use of a commonly used North American hydraulic-actuation joystick. The six different experimental conditions included combinations of three joystick stiffnesses and two movement speeds. The highest instantaneous input torque over the course of the joystick movement (not including the hard endpoint) was evaluated using the peak torque value. Angular impulse provided an indication of the sustained exposure to force. The third indicator, deceleration at the hard endpoint, was included to provide a description of impact loading on the hand as the joystick came to a sudden stop. The most important result of this work is that the dynamic torque characteristics incurred during hydraulic-actuation joystick use are substantial. While the peak torque values were not very different between the fast and slow motion conditions, the high decelerations even for slow movements observed at maximum excursion of the joystick indicate that the dynamics do matter. On the basis of deceleration at the hard endpoint and peak torque, the joystick movements that require the highest values for a combination of torque variables are the side-to-side ones. This suggests that less stiff balance and return springs should be considered for these directions than for forward and backward movements. However, if the design does not minimize acceleration, it is important that the spring stiffness not be too low since deceleration at the joystick hard endpoint will be very high causing the operator to incur large palm and finger impacts.

Off-road machine controls: investigating the risk of carpal tunnel syndrome

Occupationally induced hand and wrist repetitive strain injuries (RSI) such as carpal tunnel syndrome (CTS) are a growing problem in North America. The purpose of this investigation was to apply a modification of the wrist flexion/extension models of Armstrong and Chaffin (1978, 1979) to determine if joystick controller use in oV-road machines could contribute to the development of CTS. A construction equipment cab in the laboratory was instrumented to allow force, displacement and angle measurements from 10 operators while they completed an ˜ 30-min joystick motion protocol. The investigation revealed that both the external fingertip and predicted internal wrist forces resulting from the use of these joysticks were very low, indicating that the CTS risk associated with this factor was slight. However, the results also indicated that, particularly for the ‘forward’ and ‘left’ right side motions and for all left side motions, force was exerted by other portions of the fingers and hand, thereby under-predicting the tendon tension and internal wrist forces. Wrist angles observed were highest for motions that moved the joysticks to the sides rather than front to back. Thus, the ‘right’ and ‘left’ motions for both hands posed a higher risk for CTS development. When the right hand moved into the ‘right’ position and the left hand moved into the ‘left’ position, the wrist went into extension in both cases. Results indicate that neither learning nor fatigue aVected the results.

Effect of joystick stiffness, movement speed and movement direction on joystick and upper limb kinematics when using hydraulic-actuation joystick controls in heavy vehicles

Despite the widespread use of hydraulic-actuation joysticks in mobile North American construction, mining and forestry vehicles, the biomechanical effects that joysticks have on their human operators has not been studied extensively. Using nine unskilled joystick operators and a laboratory mock-up with a commonly used North American heavy off-road equipment hydraulic-actuation joystick and operator seat, the purpose of this work was to quantify and compare the effects of three hydraulic-actuation joystick stiffnesses and two movement speeds on upper limb and joystick kinematics as one of the initial steps towards the development of a hydraulic-actuation joystick design protocol. In addition to providing a detailed description of the kinematics of a constrained occupational task, coupled with the corresponding effects of the task on operator upper limb kinematics, results from principal component analysis and ANOVA procedures revealed a number of differences in joystick and upper limb angle ranges and movement curve shapes resulting from the various joystick stiffness-speed combinations tested. For the most part, these joystick motion alterations were caused by small, insignificant changes in one or more upper limb joint angles. The two exceptions occurred for forward movements of the joystick; the fast speed – light stiffness condition movement pattern shape change was caused primarily by an alteration of the elbow flexion–extension movement pattern. Similarly, the fast speed – normal stiffness condition movement curve shape perturbation – was caused principally by a combination of significant movement curve shape alterations to elbow flexion–extension, external–internal shoulder rotation and flexion–extension of the shoulder. The finding that joystick stiffness and speed alterations affect joystick and upper limb kinematics minimally indicates that the joystick design approach of modelling the joystick and operator upper limb as a closed linkage system should be pursued. This approach would allow one to simulate the upper limb and joystick kinematics that result from virtual changes to upper limb and joystick lengths.

A pre‐intervention benefit‐cost methodology to justify investments in workplace health

Purpose – While the rationale for interventions in a workplace to enhance employee health are well documented, practitioners have difficulty making an economic case to justify the investment required and to demonstrate positive returns on that investment. This paper aims to present case study data from an ergonomics evaluation of a call centre to demonstrate a simple, four‐step pre‐intervention methodology which provides an accounting‐based justification for funding workplace health‐related projects.Design/methodology/approach – Physical and ergonomic assessments of the workplace and employee interviews establish health risk factors. Two direct (discretionary) costs and five indirect (non‐discretionary) operational costs are evaluated. The capital investment to implement the proposed workplace changes is determined. Total net identified benefits are established and used to create accounting‐based financial metrics.Findings – Application of the methodology to the case study found worker compensation insura...

Woodlands equipment maintenance: An analysis of mechanical labor energy expenditure

Abstract The accident frequency rate of forestry field mechanics is eight times the industry average. A contributing factor is physical fatigue caused by energy-demanding tasks, difficult working positions, and hostile environmental conditions. the heart rate/oxygen uptake method was used to determine human energy expenditure levels for eight specific maintenance activities. Eight work positions were also identified, and their energy expenditure levels were recorded. Mean daily shift-level energy expenditures were found to be in excess of 10,000 kJ, equivalent to a continuous average output above 20.0 kJ per minute. The most energy-demanding task was removing engine protection plates. The most energy-demanding position was standing, with the body bent forward at the waist, over some obstacle. It is concluded that maintenance mechanics routinely work at 33% of their predicted maximal oxygen uptake level, a value that is considered to be at the top of the acceptable range for physically active male workers. At this level, the potential for an accident situation is high.

Ergonomics Codes of Practice: The Challenge of Implementation in Canadian Workplaces

Despite a reduction in the workplace injury rate for most industries in Canada, the number of compensation claims for the Canadian Forest Industry is not declining at a comparable rate. While mechanisation, particularly of tree harvesting operations, has improved injury rates in the last 5 to 7 years, the forest industry, along with similar labour-intensive industries such as mining, construction, and agriculture, continue to have unacceptable health and safety records. This review of ergonomics codes of practice focuses on the issue of implementation, as perceived by the three major stakeholders, management, employees and their unions, and government. Barriers to implementation and successful programs are discussed, as is the use of Benefit/Cost analysis as one measure of success. Three examples of successful ergonomic interventions in Canadian forestry, manufacturing, and healthcare are detailed to illustrate the effective use of Benefit/Cost analysis as a measurement tool, and as the potential path to the implementation of universal codes of practice.

A quarter of a century with the International Journal of Forest Engineering

The 1980s were very active years for the world’s forest harvesting industry. Many new machines and logging systems were being introduced, particularly in North America and Scandinavia. However, the forest engineering community had no dedicated scientific journal in which to report the results of their research, and to disseminate these findings back to the industry. Thanks to the initiative of faculty and staff in the Department of Forest Engineering, University of New Brunswick, Canada, and a dedicated international group of editorial board members, the first issue of the Journal of Forest Engineering was published in July 1989, under the editorship of Jeremy Rickards. Thus, this year is the 25th anniversary of the first international peer-reviewed scientific journal dedicated entirely and solely to forest engineering. The number of contributors and subscribers to the journal expanded rapidly and in 2000 International was added to the title, recognizing subscribers and contributors on all continents. Much has happened during the journal’s first quarter of a century, both in terms of how forest operations are conducted as well as of research focus and the conditions for the researcher’s publishing in the journal. These developments unfold quite clearly when following the happenings of and the publications in the IJFE. Here we, all five of the editor-in-chiefs during the 25 years, summarize these developments, as well as provide behind-the-scene facts. Naturally we also provide a view on the future of IJFE and on forest engineering research in general.

Carpal Tunnel Syndrome ­ Identifying the Risk Factors in Forest Industry Operations

Given that the forest industry has diversified from primarily manual extraction and processing of trees to include a wide variety of occupations and job functions, many of which require employees to make repetitive, high force motions of the hands and wrists, suggests that this group of workers may be at risk for developing carpal tunnel syndrome (CTS). To raise awareness, this paper provides an indication of the CTS risks associated with four classes of forestry occupations and gives some avoidance guidelines for the prevention of this disorder.