GOVERNMENT CONSUMER SAFETY RESEARCH

Department of Trade and Industry

SECTION 1. INTRODUCTION AND BACKGROUND

This report summarises the results of research conducted by Nottingham University on behalf of the Consumer Affairs Directorate of the Department of Trade and Industry (DTI) to provide designers with ergonomics data for use in the design of safer products.

The University of Nottingham has recently worked with DTI to produce a series of publications containing ergonomics data. The three publications on children, adults and older adults (‘Childata’, ‘Adultdata’ and ‘Older Adultdata’) contain the most up-to-date anthropometric and physical strength data for countries around the world. However, their production has highlighted important ‘gaps’ in the data available for direct use in product design.

This report describes a two stage research programme which was undertaken to try to address some of these data ‘gaps’. Potential needs for design-applicable data were identified and prioritised in Stage 1 of the project, and in Stage 2 new data were collected to meet some of those needs. The report consists of three main sections:

1. Introduction and background

2. Data sheets

3. Appendices

In Section 1 of the report, the two stages of the research are introduced and the methodologies described. In Section 2, detailed descriptions and results of the data collected as part of Stage 2 of the study are presented in the form of ‘data sheets’, and in Section 3, the statistical analyses performed are presented as appendices.

The data sheets, detailed in section 2, show the new data for all age groups. For easier reference these data have been colour coded by age to fit in with the age ranges in CHILDATA, ADULTDATA and OLDER ADULTDATA. The colours used to highlight each age range is that used for the background colour on the cover of each publication. For example CHILDATA is white ( ), ADULTDATA is grey ( ) and OLDER ADULTDATA is pink ( ).

Stage 1 – Identification and prioritisation of data ‘gaps’

To identify and prioritise the types of data most needed for design purposes, a survey of users of ergonomics data was carried out. Around eight hundred and fifty designers, manufacturers, ergonomists, consumer safety groups and product testing laboratories were contacted by postal questionnaire. Respondents were asked to detail the sort of data or information which they have needed for their own design purposes but have found difficult to source. In total, eighty responses were received. Most responses requested a need for physical strength data for all age groups: data which could be directly applied in the design process. In addition, it was felt that data should describe generic functions, rather than be product-specific, so that it can be used in as many design applications as possible. Based on these findings, a series of six realistic but generalisable strength measurements were identified as summarising the most important data needs:

1. finger push strength

2. pinch-pull strength

3. hand grip strength

4. wrist-twisting strength

5. opening strength

6. push and pull strength

A programme of research was instigated and new data were collected in Stage 2 for all six ‘gaps’.

Stage 2 – Data collection methodology Subjects To provide designers with a comparable set of design-applicable data for all age groups, children through to older adults were measured in the study. Around 150 British subjects aged between 2 and 86 years were measured for each of the six strength exertions. Subjects were grouped into 5 or 10 year age bands, with around 15 individuals in each band, although this varied slightly between each measurement. Subject numbers are described separately for each force measurement in the data sheets (Section 2). The anthropometric details of the subjects are described in the corresponding appendices. Subjects were not selected to be representative of socio-economic criteria.

Measurements

Measurements were taken for a total of six different force exertions, and are summarised below. Detailed descriptions of each measurement can be found in Section 2.

• finger push strength – pushing with the pad of the thumb and index finger in a forwards and downwards direction.

• pinch-pull strength – pinching and pulling with 1 hand at three pinch distances. Two pinch types were tested: pulp pinch (pad of the thumb in opposition to pad of the index finger) and chuck pinch (pad of the thumb in opposition to the pads of both the index and middle fingers).

• hand grip strength – 1 and 2 handed strength when gripping a series of three rectangular handles of varying size.

• wrist-twisting strength – torque (clockwise) using 1 hand on a series of six handles and controls

• opening strength – torque (anti-clockwise) on a series of replica jars with smooth and knurled textured lids of various diameters.

• push and pull strength – pushing and pulling with 1 and 2 hands on a cylindrical bar, and pulling with 1 hand only on a convex knob.

Procedure

Subjects were asked to exert their maximum strength at all times, described as the highest force he or she could exert without causing injury. Subjects were instructed to build up to their maximum strength in the first few seconds, and to maintain maximum strength for a further few seconds. Where only one-handed strength was measured, subjects were instructed to use their dominant hand. Subjects performed two strength exertions (lasting five seconds) for each experimental condition, and were given a two minute rest interval between each exertion. Subjects stood during testing and were free to adopt their own posture. The testing device was adjusted and positioned at each subject's elbow height (with the exception of opening strength and hand grip strength where the equipment was freely moveable). Subjects were encouraged to exert maximal effort during testing and were able to obtain visual feedback from the testing device.

Equipment

Finger push strength, pinch-pull strength and wrist-twisting strength were measured on a series of specially made handles which were attached to a Mecmesin™ Advanced Force Gauge (AFG 500N). Hand grip strength was measured using a Handgrip Dynamometer (MKIIIa) made by the Medical Physics Department, Queens Medical Centre, Nottingham, UK. Opening strength and push and pull strength were measured with the aid of strain gauges which were attached to custom-made equipment.

Results

The results for each of the six measurements are presented in turn as separate ‘data sheets’. Each measurement is defined, and the method of measurement, number of subjects measured, and the data collected are detailed. Data are presented separately for males and females and are also shown graphically. Differences in strength due to age and sex, as well as differences between experimental conditions, were analysed by means of a t-test, and these findings are presented in Appendices 1 to 6. A correlation coefficient matrix detailing the relationship between all measurements can be found in Appendix 7.

Effect of sex

For most measurements, no significant differences in maximum strength were found between male and female children (2-15 years). However, in adults aged 16 years and over, males were generally found to be significantly stronger than females.

Effect of age

Strength was found to increase with age throughout childhood, to peak in adulthood, and then to decrease with age from around 50 years. Throughout childhood, each successive age group (2-5, 6-10, 11-15 years) was found to be significantly stronger than the previous group for all six measurements. Generally, however, no significant differences in maximum strength were found within the adult (16-20, 21-30, 31-50 years) or older adult (51-60, 61-70, 71-80, 81-90 years) age groups. For most strength exertions, adults (16-50 years) were found to be significantly stronger than older adults (51-90 years), who in turn were significantly stronger than children (2-10 years). No significant differences in maximum strength were generally found between 11-15 year olds and 60-80 year olds, or 6-10 year olds and 80-90 year olds.

Using the data

When using the data in this study, there are several factors which must be considered:

• Little or no correlation was found between the six measurements, suggesting that the forces exerted were action-specific. That is, the size, shape and orientation of the handle or control, the direction of force and the number of hands used all affected the amount of force that could be exerted.
• Within each measurement, significant differences were found between the experimental conditions. For example, opening strength was significantly affected by the size and texture of the jar lid, as was hand grip strength by the size of the handle and number of hands used. Exceptions to this finding were finger push strength and push and pull strength, where no significant differences due to the direction of force were found. That is, no differences in strength were found between pushing forwards and downwards with either the thumb or index finger, and similarly when pushing and pulling with both 1 and 2 hands on a vertical bar, or 2 hands on a horizontal bar.
• No restrictions were placed on posture and subjects were able to grip and manipulate the various handles and knobs as they chose (with the exception of pinch-pull strength). The amount of force that can be exerted in such a free posture is known to be greater than that generated in a standardised posture (where subjects are often instructed to stand upright with their elbows flexed to 90 degrees).
• Subjects were instructed to exert their maximum strength (the highest force he or she could exert without causing injury).

Care should therefore be taken when using the data, particularly when applying it to other design scenarios, where, for example, individuals may be restricted in the posture that they can adopt, where comfortable rather than maximal force is required, or where data are needed for handles and controls of a different size, shape or position.

SECTION 2. DATA SHEETS

1. Finger push strength

Description

Maximum static forwards and downwards pushing force of the index finger and thumb, exerted for five seconds, in Newtons (N).

Method

The subject stands in front of the measuring device and adopts a free posture. A static pushing force is exerted with the pad of the index finger or thumb of the dominant hand on a circular force plate (i.e. the force plate doesn’t move). Subjects push in a forwards or downwards direction. Subjects are instructed to build up to their maximum strength in the first few seconds and to maintain maximum strength for a further few seconds.

Handle type and size

Circular force plate (diameter 20mm, depth 2mm), positioned at subjects elbow height.Anthropometric variables (stature, weight, elbow height, hand length and hand breadth) for all subjects can be found in Appendix 1a.

Circular force plate	Experimental trial: Pushing downwards with the index finger

Subject numbers 148 subjects were measured:

Analysis

Effect of sex
For all four measurements (pushing forwards and downwards with the index finger and thumb), no significant differences were found between male and female children (2-15 years). However, in all adult and older adult age groups (16-80 years), males were found to be significantly stronger than females (Appendix 1b).

Effect of age
Finger push force increases with age throughout childhood, it peaks in adulthood, and then decreases with age from around 50 years. Throughout childhood, each successive age group (2-5, 6-10, 11-15 years) was found to be significantly stronger than the previous for all four measurements. No significant differences were found within the adult (16-20, 21- 30, 31-50 years) or older adult (51-60, 61-70, 71-80, 81-90 years) age groups, however, differences were found between the groups, in that adults (16-50 years) were found to be significantly stronger than older adults (51-90), who in turn were stronger than children (Appendix 1c).

Effect of finger type used and direction of force
The direction of force appears to have little or no effect on maximum finger push strength, as no significant differences were found between forwards and downwards push (with either the index finger or thumb). The finger used, however, did; pushing with the thumb generated significantly higher forces than pushing with the index finger (Appendix 1d). Of the four measurements, children (2-15 years) exerted the greatest force when pushing forwards with the thumb, whilst adults (16-50 years) and older adults (51-90 years) generally exerted the greatest force whilst pushing downwards with the thumb. Correlation coefficients for all 4 measurements can be found in Appendix 1e.