Chris J. Snijders

Revision of the design of a standard for the dimensions of school furniture

In this study an anthropometric design process was followed. The aim was to improve the fit of school furniture sizes for European children. It was demonstrated statistically that the draft of a European standard does not cover the target population. No literature on design criteria for sizes exists, and in practice it is common to calculate the fit for only the mean values (P50). The calculations reported here used body dimensions of Dutch children, measured by the authors Department, and used data from German and British national standards. A design process was followed that contains several steps, including: Target group, Anthropometric model and Percentage exclusion. The criteria developed in this study are (1) a fit on the basis of 1% exclusion (P1 or P99), and (2) a prescription based on popliteal height. Based on this new approach it was concluded that prescription of a set size should be based on popliteal height rather than body height. The drafted standard, Pren 1729, can be improved with this approach. A European standard for school furniture should include the exception that for Dutch children an extra large size is required.In this study an anthropometric design process was followed. The aim was to improve the fit of school furniture sizes for European children. It was demonstrated statistically that the draft of a European standard does not cover the target population. No literature on design criteria for sizes exists, and in practice it is common to calculate the fit for only the mean values (P50). The calculations reported here used body dimensions of Dutch children, measured by the authors Department, and used data from German and British national standards. A design process was followed that contains several steps, including: Target group, Anthropometric model and Percentage exclusion. The criteria developed in this study are (1) a fit on the basis of 1% exclusion (P1 or P99), and (2) a prescription based on popliteal height. Based on this new approach it was concluded that prescription of a set size should be based on popliteal height rather than body height. The drafted standard, Pren 1729, can be improved with this approach. A European standard for school furniture should include the exception that for Dutch children an extra large size is required.

A newly designed ergonomic body support for surgeons.

BackgroundOne of the main ergonomic problems during surgical procedures is the surgeon’s awkward body posture, often accompanied by repetitive movements of the upper extremities, increased muscle activity, and prolonged static head and back postures. In addition, surgeons perform surgery so concentrated that they tend to neglect their posture. These observations suggest the advantage of supporting the surgeon’s body during surgical procedures. This study aimed to design a body support and to test its potential.MethodsThe optimum working condition for a surgeon is a compromise between the spine and arm positions and the level of effort and fatigue experienced performing a procedure. The design vision of the Medisign group has led to the development of an ergonomic body support for surgeons that is suitable for use during both open and minimally invasive procedures. The feasibility of the newly designed ergonomic body support was assessed during seven surgical procedures. Electromyography (EMG) was performed for back and leg muscles using the body support in an experimental setting.ResultsSix of seven participating surgeons indicated that the body support was comfortable, safe, and simple to use. The EMG results show that supporting the body is effective in reducing muscle activity. The average reduction using chest support was 44% for the erector spinae muscle, 20% for the semitendinosus muscle, and 74% for the gastrocnemius muscle. The average muscle reduction using semistanding support was 5% for the erector spinae, 12% for the semitendinosus muscle, and for 50% for the gastrocnemius muscle.ConclusionThe results of this study imply that supporting the body is an effective way to reduce muscle activity, which over the long term may reduce physical problems and discomfort. Additionally, the product supports the surgeon in his natural posture during both open and minimally invasive procedures and can easily be adapted to the current layout of the operating theater.

New ergonomic design criteria for handles of laparoscopic dissection forceps.

BACKGROUNDnThe shape of laparoscopic instrument handles can cause physical discomfort. This problem may be ascribed to a lack of standards for instrument design. In this study, new ergonomic requirements for the design of laparoscopic dissection forceps were created. Three representative handles (a Karl Storz [click-line] scissors handle, an Access Plus scissors handle, and an Aesculap cylindrical handle) currently available on the market were evaluated according to the new list of ergonomic criteria.nnnMATERIALS AND METHODSnThe handles were subjectively (questionnaire) and objectively (video analyses) tested in order to find out whether the new requirements are valid for the evaluation and design of instrument handles.nnnRESULTSnThe outcome of the subjective and objective tests matched the predictions by the new criteria list. New criteria were introduced (neutral wrist excursions), and existing general criteria were specified (e.g., a minimal contact area of 10 mm). Significant differences were found among the three handles. The Storz handle met 8 of the 10 requirements, the Access handle met 5, and the Aesculap handle met only 4.nnnCONCLUSIONSnThe new list of ergonomic requirements is a valid tool to determine the ergonomic value of a handle for laparoscopic dissecting tasks. It gains its strength from its specialized character. Significant differences were found among the three tested handles. Cylindrical handles were inferior to scissors handles.

Oblique abdominal muscle activity in standing and in sitting on hard and soft seats

The activity of the oblique abdominal muscles was investigated with the trunk in unconstrained, symmetrical and static postures. Electromyographic recordings in six healthy subjects revealed that in all subjects the activity of both the internal and the external obliques is significantly higher in unconstrained standing than in supine posture. Activity of the internal oblique was higher than that of the external oblique abdominal. The sacrospinal, gluteus maximus and biceps femoris muscles showed practically no activity in unconstrained erect posture. During unconstrained sitting both oblique abdominals are active. In most subjects the activity of the oblique abdominals was significantly smaller when sitting on a soft car seat than when sitting on an office chair with a hard seat. The possibility is discussed that contraction of the oblique abdominals in unconstrained standing and sitting may help in stabilizing the basis of the spine and particularly the sacroiliac joints. During standing and sitting the oblique abdominal muscles apparently have a significant role in sustaining gravity loads. RELEVANCE: Back pain and pelvic pain are often experienced in prolonged standing and sitting postures. In these postures the oblique abdominals are shown to be active. The present study gains clinical significance by the studies showing relatively small oblique abdominal muscle strength in patients with low back pain. A soft seat may be helpful in treatment and prevention, because it substitutes oblique abdominal muscle activity.

Improved usability of a new handle design for laparoscopic dissection forceps

Background: Recent studies have shown that the shape of most instrument handles causes user discomfort and that none of the handles currently available on the market satisfies all ergonomic criteria. Therefore, we designed a handle with improved usability; i.e., it is easier to manipulate and its use entails less risk of injury for the operator. The aim of this study was to demonstrate that the intended improvements of the new design were successful. Methods: Six handles representative of the types that are currently available were compared with the new version. Eight surgeons used the seven handles during a precision task and a rough task in a pelvi-trainer. A questionnaire and video analyses were used to assess the usability of the handles. Results: Based on the responses to the questionnaire, we determined that there were significant differences between the new handle and the Aesculap handle (means of rotation and angle between handle and shaft). No significant differences were found between the new handle and the five other handles. The video analyses (documenting extreme vs neutral wrist excursions) showed significant differences between the new handle and the six other handles. Conclusion: Compared to the six existing handles, the new handle has significantly improved usability; in particular, its hinged design obviates the need to make extreme wrist excursions.

Improvement of the laparoscopic needle holder based on new ergonomic guidelines

Background: The aim of this study is to create new ergonomic guidelines for the design of laparoscopic needle holders. Methods: An ergonomic literature study, observations in the operating room, handle–shaft angle measurements, and anthropometric data were used to compile new ergonomic criteria, specified to the function of a laparoscopic needle holder. Based on these guidelines a new needle holder was designed. The prototype and three currently available needle holders were evaluated according to the new guidelines. In addition, a pelvi-trainer test was done to measure the extreme wrist excursions. Results: The ergonomic evaluation of three commonly used handles and the new prototype indicate that the new handle is an ergonomic improvement in the field of laparoscopic needle holders: only the new handle satisfies all criteria. This is validated by the results of the pelvi-trainer test, which showed that the new prototype significantly (p < 0.001) reduced the extreme wrist excursions. Conclusion: The new design guidelines for a laparoscopic needle holder result in an ergonomic improvement of the instrument.

Geometric Data of Hallux Valgus Feet

The aim of this study is to find basic quantitative geometric data that may contribute to the understanding of the etiology of hallux valgus. Embalmed specimens with existing hallux valgus (N = 39) were dissected; 28 variables were measured with a Vernier caliper gauge and toe goniometer. Correlations between pairs of independent variables were calculated. Linear dependency of the hallux angle, varus angle, and the width of the forefoot on a number of independent variables was analyzed by multiple linear regression. A least squares method and a stepwise procedure were used. The distance from the tendon of the flexor hallucis longus muscle to the head of the first metatarsal bone explains more than other variables the variation in hallux angle and width of the forefoot. A widened forefoot is significantly correlated with both hallux and varus angles. The interrelation of the predictor parameters illustrates the complicated hallux valgus phenomenon.

Biomechanical analysis of the dimensions of pilot seats in civil aircraft.

The dimensions of pilot seats from five different types of civil aircraft were measured and the results compared with existing standards and biomechanical criteria. It was apparent that these seats failed to meet requirements, particularly in the effective depth and inclination of the seat and in the height of the lumbar support and the armrests. Hence, none of these seats made it possible for the pilot to establish a comfortable sitting posture. In comparison with aviation standards, the anthropometric dimensions were not satisfactory, meeting only 4-7 out of 10 requirements. The dimensions based on biomechanics were even less satisfactory, meeting only between 1 and 3 requirements out of 7.

Shoe design for prevention of injuries in sport climbing

Foot injuries and deformations are more frequent at higher levels of sport climbing. These are accepted as unavoidable because it is assumed that, for optimal performance, a prerequisite is the wearing of a shoe, which is too tight and has an unnatural shape. Based on a biomechanical analysis, we came up with a different approach to shoe design. By using regional thinning of the sole, easy flexion and extension of the toes is made possible. The form of the shoe conforms to the natural form of the foot, the shoe closure provides a close fit for feet with width differences of up to 20 mm and a shoe-sizing system was developed. After testing prototypes, we conclude that the new shoe design can contribute to the prevention of foot injuries and deformations in sport climbing.

Free shoulder space requirements in the design of high backrests

The objective of this study was to determine the influence of scapular support on the effects of lumbar support and to prove that a high and straight backrest is inappropriate. In literature the importance of a lumbar support is noted, although data about optimal dimensions is an under-researched topic and in earlier studies on force distribution and muscle activity the backrest had a fixed form. The lumbar support is needed to maintain the lumbar lordosis but no studies deal with the question of the precise dimensions of the backrest at shoulder level. With a specially designed apparatus, forces on shoulder and seat were measured separately, and the force on the pelvis calculated, while varying seat and backrest inclination within the range from 0° to 17°. Seat-to-backrest angle (at the level of lumbar support) was kept constant at 90°. The distance between the tangent to the lumbar support and the parallel tangent to the scapular support was varied from 0, 2, 4, 6 and 8 cm. This distance is called the free shoulder space. Electromyography was measured at the erector spinae at the levels of the L1, T8 and T5 vertebrae. For all seat angles, a free shoulder space of d=0 cm resulted in the highest back muscle activity. In agreement with the biomechanical model, EMG activity reduced with an increase of seat tilt and increase of free shoulder space. With increasing free shoulder space, a larger part of the total backrest force was carried by the lumbar support. This study shows that a high and straight backrest overrules lumbar support. Offering free shoulder space of at least 6 cm reduces back muscle activity and allows for lumbar support.