Adapting the force characteristics of a staple gun to the human hand.

Three prototype staple guns with modified force characteristics were compared with a commercially available standard staple gun with a linearly increasing force resistance during squeezing. The force characteristics of the prototypes were more or less adapted to the force characteristics of the human hand, and in one of the staple guns the general force level was also reduced by one third. Evaluation instruments were electromyography of the forearm flexors and extensors, subjective rating of forearm exertion and subjects' free comments about the four tools. Twelve professional craftsmen were recruited as test subjects. The results show significantly lower readings for two of the three prototypes compared with the standard gun in electromyography as well as subjective ratings. The squeezing times are also reduced for two of the prototypes. It is concluded that the choice of force characteristics of a staple gun is important both to minimize forearm muscular exertion and to increase tool efficiency.

Fatigue and recovery during and after static loading.

Subjectively assessed endurance time (ET), resumption time (RT) and perceived discomfort, pain or fatigue (PD), and objectively measured maximum force-exerting capacity were investigated for varying loads and durations of a pushing task with two repeated trials. Beyond the main results quantifying how the load scenario affected ET, RT and PD, three additional results are of note: (1) although the maximum pushing force did not change between trials, shorter ET, longer RT and higher PD indicated accumulation of fatigue in Trial 2; (2) the PD ratings showed a trend with a linear increase during loading and a curvilinear decrease during recovery; and (3) the RT and the load level for different relative loading times were found to have an unexpected U-shaped relationship, indicating lowest fatigue at the intermediate load level. These results can be used to model a more sustainable and productive work-recovery ratio.

The effect of wrist orthoses on forearm muscle activity.

A general hypothesis is that a wrist orthosis reduces the wrist extensor muscle load. The aim of this study was to investigate the effects of a completely stiff wrist orthosis (SO) and a commercially available wrist orthosis (CO) on flexor and extensor electromyographic (EMG)-activity in a standardised intermittent gripping task and during standardised manual work tasks. Surface EMG from two forearm flexor and two extensor muscles was recorded. The target grip forces were 5%, 20% and 40% of maximal voluntary contraction (MVC). During the grip contraction phase CO had no effect on the EMG-readings. SO resulted in higher EMG activity than when gripping with CO and with no orthosis (NO), especially when gripping with 40% MVC. During the relaxation phase neither CO nor SO had any effect on the extensors. For the flexors the SO gave higher EMG-readings than when gripping with CO and NO, especially at 40% MVC. In conclusion the wrist orthoses tested did not reduce the EMG-activity from the flexors or the extensors during gripping or manual tasks.

Corporate initiatives in ergonomics--an introduction.

Examples in the literature of corporate initiatives in ergonomics are reviewed. Different types of programmes are identified with ambitions ranging from time-limited interventions to continuous processes. Common elements are health surveillance, workstation design and choice of tools, product design, quality aspects, participative aspects and education, training and information. The implementation of ergonomics programmes varies substantially depending on the type of company, and company policies and organisation. Some of the most developed ergonomics programmes originate from the automobile industry. Other businesses with many established programmes are the electronics industry, the food industry and the office environment. A participative approach, as well as ergonomics expertise, are crucial ingredients for a successful programme. The scientific evaluation of ergonomics programmes, especially in economical terms, is in too many cases insufficient or missing. Furthermore, links to company core values such as quality improvement are often lacking. Programmes in ergonomics are still often seen as solely a matter of health and safety. Only a few companies have reached the state where ergonomics constitutes an integrated part of the overall strategy of the enterprise.