2015 to present

This work is part of a larger study to understand how we can measure dexterity more effectively and how it relates to everyday tasks such as bathing, dressing and in this case accessing packaged food. 

It has long been acknowledged that access to packaging is a serious problem for older people. As we age there is a natural decline in our strength, dexterity, and cognition. This is before we talk about any issue of chronic illness such as arthritis, which unfortunately is also prevalent in older people and can have a significant effect of a person’s ability to manipulate objects such as packaging. 

Much of the work undertaken by researchers on the inability of older people to access food packaging, has concentrated on understanding issues around strength, with some work on semantics and visual acuity (cognition). Much less work has looked at the ability to manipulate packing or the dexterity needed to access the contents. It is likely that there is less work in this field since defining dexterity is complicated and measuring is not necessarily straightforward.

Researchers and healthcare professionals use many ways to measure dexterity from standard ‘pick-up’ tests to dedicated hand assessment protocols. One of the most common, with a large amount measured data, is the ‘Perdue Pegboard’ test developed by American researchers following World War 2, and is widely used in the field of rehabilitation. 

Measuring hand movements is complex but can be achieved using a range of techniques such as goniometers and optical methods such as video photogrammetry or motion tracking using infra-red cameras. Hence, this work describes part of a quantitative study that aimed to analyse motion coordination patterns across digits 2–5 (index to little finger) during interactions with three of the most common types of packaging: plastic bottles, jars and crisps packets, and comparing those interactions with a common measure of dexterity, the Perdue Pegboard. Ten subjects (six male participants and four female participants) were examined whilst reaching forward to grasp and open a 300 ml plastic bottle and a 500 g jar. A 10-camera optoelectronic motion capture system measured trajectories of 25 miniature reflective markers placed on the dorsal surface landmarks of the hand. Joint angular profiles for 12 involved flexion–extension movements were derived from the measured coordinates of surface markers. If we talk about finger movements, we can say where fingers move together in a similar pattern as highly correlated, where the fingers move in separate patterns as lowly correlated.

The results showed that finger correlations vary widely across the differing pack formats with the crisps having the lowest finger movement correlation and the jar having the highest. Speed and jerk metrics of the fingers (i.e. how fast they move and the rate of change of that movement) were also seen to vary across the various pack formats. However, finger correlations were seen to be more relevant to perceived dexterity of pack opening than finger speeds and jerk motions. 

This has implications for pack design in that high dextrous demand is determined by finger correlation, not say speed and therefore packs should be designed that promote smooth and highly correlated finger movements to reduce issues around dexterity and inability to access the contents.

The project has been funded by the Mexican Government and conducted by Professor Alaster Yoxall of ADMRC, Sheffield Hallam University, and Dr Victor Gonzalez and Dr Jennifer Rowson of the Department of Mechanical Engineering, The University of Sheffield.