Sit-to-stand movement (STS) is a familiar activity that is frequently performed in daily life. The ability to perform STS movements is fundamental to normal activities of daily living and also a prerequisite of locomotion (walking) activity. Moreover, an unassisted STS movement is an essential skill that determines the functional level of a person, especially in older people who have had general deterioration in the ability to perform effortful movements. STS movements are a good indicator of mobility and frailty in older adults, and therefore often targeted in rehabilitation programmes.
The majority of studies in STS movements have focused on four major
applications, including chair design, analysis of normal and abnormal STS movements, biomechanical modelling and intervention method. To our knowledge, only a few studies have investigated the potential of motor imagery (MI) during STS tasks, either as a way of accessing higher-level planning of complex body movements or to develop intervention procedures for enhancing performance and
learning. In fact, MI is practical to provide and low in cost and time, so this
technique should be valuable to use in rehabilitation as an alternative or additional technique combined with other techniques, such as physical practice. There is evidence suggesting that kinesthetic (internal) imagery (focusing on one’s own
movement) is more effective in activating motor pathways than imagery focused on
environment). However, how these results relate to the case of STS movements is not known. The effects of directing attention to body-internal or body-external aspects of movement coordination on imagery or execution need to be examined.
Focus of attention is a common variable used in either motor learning research or rehabilitation in order to improve motor performance and learning. Based on work in exercise science, two types of attentional focus are of particular interest – external focus (directed to the effects of movement in the environment) and internal focus (directed to the articulation of the movement itself). In studies of motor performance, it has been found that directing attention to the effects of movements on the environment (external focus of attention) results in greater fluency than directing attention to the movements (internal focus of attention).
MI approaches have been used in clinical or rehabilitation settings with the
intention of improving effectiveness and efficiency of training, but the effects of
attentional focus have been studied mostly in the context of executing motor skills.
It is of interest whether focusing attention on movement articulation (body-internal
focus) or away from the body and to the perceptual effects of movements in the environment (body-external focus) during MI and motor execution differ systematically in the context of STS movements, and whether any such differences are sensitive to the process of ageing.
To clarify the impact of attentional focus on motor imagery and performance, this study directly compared the effects of external versus internal focus on physical and imagined instances of STS movements. Knee extensor function and weight
bearing on the feet are known to be essential factors in determining performance in
thighs, or the pressure under their feet, as variants of body-internal focus during imagined and physical STS movements. In the case of body-external focus, we asked participants to fixate a visual target on the wall (at eye-level when standing), and
focus on the change in viewpoint relative to the target. We measured how these
conditions affected the self-reported movement times and the ground reaction forces during imagined STS movements. We also measured the self-reported and actual movement times of physical STS movements, and the smoothness or stability of the
physical movements under these internal and external focus conditions.
Older people are known to accrue deficits in motor planning, control and execution that increase reliance on visual information to guide movements as proprioceptive control deteriorates with decreasing muscular strength. This suggests that young and older participants may respond differently to changes in attentional focus from body-internal (proprioceptive) to body-external (visual) aspects of coordination. However, the direction of any such difference is unclear. Older people may benefit from external (visual) focus, or from focusing on proprioceptive information (if deliberately directing attention counteracts the deficits they have in utilizing this type of information).
This study also examined two further aspects of STS performance that have practical importance and also theoretical significance. The first aspect concerned the height of the seat from which STS movements are made. A variety of seat heights can be found in various settings, such as in houses, offices and even in hospitals, and changing this parameter is known to alter the biomechanical demands of STS movements and also the strategies employed in executing them. In particular, standing up from a lower seat height (especially lower than knee height) adds significantly to the required muscular effort, which may amplify the differences in
performance (and maybe also imagery) between young and older adults. The second aspect concerns manual activity concurrent with STS movement (e.g., standing up with a drinks cup or food plate balanced in one hand). This is effectively a divided attention task, something that is known to challenge older people to a greater extent. The effects of deliberately targeting attention to internal or external aspects of coordination on these task situations are not well understood, and what any age- related differences occur during execution and imagery are useful to study.
Finally, this study also began to test the effects of internal versus external attentional focus on a motor-imagery based learning protocol. During STS movements, the weight of the body tends to be supported to a greater extent by the dominant leg, such that the force distribution is laterally asymmetrical. Although this strategy may be adaptive in healthy individuals, unilateral strength loss due to brain trauma can induce task conditions whereby altering the symmetry of force application can become a training goal. In the final experiment of this study, we implemented a learning protocol using motor imagery training, and asked participants to try to make their STS movement more symmetrical. We were interested in the effects of attentional focus and ageing on the effectiveness of training in this task.
In summary, the present study began with a comparison the effectiveness of body-internal or external attentional focus during physical and imagined STS movements in healthy young and older adults. It then examined the effects of changing seat height (i.e., level of effort) and manual secondary task (i.e., divided attention). Finally, it tested whether imagery-based STS training might be affected by the attentional focus manipulation.