Is Movement Strategy a Matter of Age?
How we should lift things up from the floor has always been a source of debate in both the worlds of healthcare AND fitness. Many studies have previous looked at different lifting techniques from the squat to the semi squat and also the stoop lift. Research has also explored the effect of object size and weight, height from which it is picked up, and the speeds at which it is lifted on the performance of the task. Functional capacity factors such as gender and cardiovascular and muscular capacity have also been explored.
The key question posed in this piece of research was to better identify the postural strategies adopted during a task requiring collection of objects placed at floor-level by performing a multi-segment analysis. Within this question the researchers also set out to determine the internal factor of age on lifting technique and if there was variability within age groups and technique.
Three main questions were identified:
- Is there a dominant strategy characteristic of each age group?
- Does the same person use more than one strategy?
- Is this level of variability influenced by age or the pace of work?
Methods/What they did:
63 right-handed men were recruited, all working in physically demanding jobs. These criteria were designed to ensure similar functional capacities between the subjects. They were recruited to fit into 3 main groups to stratify the results based on age. These groups were 30-35 years, 45-50 years and 60-65 years. Functional capacity measures were taken such as upper and lower limb strength measures and speed and flexibility tests.
The task was fairly complex with subjects being asked to perform an “assembly task in conditions similar to those encountered at an assembly-line workstation”. This required collecting different shaped and weighted objects from floor level. This happened over two work cycles that consisted of 20 minutes each. These were also performed at a number of different paces from comfortable to rapid.
The experimental setup left subjects free to choose the position of their feet when performing the task allowing them more opportunity to be creative when collecting objects from floor-level. The collecting task used in this study was part of a succession of tasks.
The strategies adopted during these tasks were recorded via 3D video analysis and forces and moments were also measured via a force plate. 17 variables were used to model the final multi-segmental analysis.
Results/What they found:
7 main strategies of performing the lifting task were identified. These were 5 types of squat and two types of stoop lift. No dominant strategy amongst the 7 was identified and also the amount of strategies used was not affected by the changes in pace adopted. There was however an interaction between the age of the participants and the amount of different strategies that they used. The number of different strategies to perform the task decreased with the age of the participant.
No previous injury history or current pain was identified in the inclusion criteria in this paper. Because movement variability can also be affected by previous or current levels of pain, this perhaps should also be factored in. In fairness to the authors however, this was not really an aim of the paper.
The highlighting of natural movement variability within and between subjects is always important clinically. This is objective data to offset the many less objective opinions available both in the media and social media. This also affects manual handling advice as we are often told there are right and wrong ways to lift and then educate people based on this advice. This binary view of right and wrong ways to move and lift do not appear to be apparent from the data here, with multiple strategies employed by the participants although this did decrease with age. Further sub group analysis with previous or current pain may enlighten us further with regards to therapy.
This means that the way we teach lifting could also involve elements of being variable within and between exercises. This could be another option to help those we work with get back to normal and healthy movement strategies. This may be in direct contrast to the repetitive ways we currently view the implementation of exercise around biomotor factors such as strength, flexibility and stability.
A strength of the study is the way in which they set up the task in that it allowed multiple ways to perform the task as you might see within a workplace. This should also inform us that if we want to set up tasks or exercises to allow variable options to emerge then the environment, equipment and instructions must allow this. We often constrain the amount of movement options available through exercise equipment, limited environmental options and lots of ‘safety’ instructions. The number of instructions provided has previously been shown to limit degrees of freedom and also may perpetuate or reinforce the concept of right and wrong ways to move and exercises being inherently unsafe.
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Gilles M and Wild P (2018) Grasping an object at floor-level: Is movement strategy a matter of age?. Applied Ergonomics, 70, 34-43.