Elsevier

Human Movement Science

Volume 25, Issue 2, April 2006, Pages 257-274
Human Movement Science

The effects of unilateral grab rail assistance on the sit-to-stand performance of older aged adults

https://doi.org/10.1016/j.humov.2005.11.003Get rights and content

Abstract

This study investigated the effects of unilateral grab rail assistance during the sit-to-stand transfer to develop an understanding of lower limb joint mechanics and whole body movement patterns. External reaction forces at the grab rail and floor interfaces were also investigated to understand the nature of the assistance provided by the introduction of unilateral upper body assistance. While 12 older aged adults performed the sit-to-stand, three-dimensional body segment kinematics were recorded to determine lower body joint motion and whole body centre of mass motion. Grab rail reaction forces and bilateral ground reaction forces were recorded to determine external reaction forces and lower body joint kinetics. Grab rail assisted conditions were compared with unassisted transfers. During grab rail assistance, a systematic asymmetry was introduced to lower limb joint kinetics, without noticeable alterations to peak lower body joint motion and whole body movement patterns. Ipsilateral net joint moments and powers decreased in the ankle and hip and increased in the knee, while the contralateral net joint moments and powers increased in the hip and decreased in the knee. Joint kinetic and kinematic responses suggest a motor control strategy that maintains symmetric sit-to-stand movement patterns by adjusting bilateral muscle control when a unilateral external reaction force is provided. Understanding the mechanical assistance that is generated during the sit-to-stand will facilitate optimal design of grab rails for older aged adults and may contribute to design for specific pathologies. Such design implementation will influence the ability of older aged adults to remain independent in the community.

Introduction

Population ageing is occurring in all developed countries (Kendig & Mc Cullum, 1986). As a result of this trend, the proportion of the community requiring additional strategies to remain independent is likely to increase. Consequently, there will be greater demand for devices that provide assistance during activities of daily living, such as a hand rail or grab rail during the sit-to-stand transfer. Grab rails have the potential to increase the safety and mobility of a larger proportion of the community that will suffer from impairment of movement. It is necessary to have a clear understanding of the mechanical interactions between the users and the assistive device during sit-to-stand so that the rail may be used optimally and appropriately.

Qualitative assessment of grab rail function suggests that it assists balance and propulsion, and reduces muscular effort (Sanford, Arch, & Megrew, 1995). Standards exist (for example, the Australian standard AS1428.1) to provide appropriate design specifications for grab rail installation into public and private locations, such as toilet facilities (Standards Australia, 1998). These standards are based on minimal research using small samples of convenience. Further, no published biomechanical data could be found to explain the nature of the mechanical assistance provided by a laterally placed grab rail during the sit-to-stand transfer.

Upper and lower body segmental coordination is essential when performing the sit-to-stand to maintain dynamic stability over a changing base of support (BOS), (Carr, 1992, Linden et al., 1994, Pai and Rogers, 1990, Vansant, 1992). Movement of the arms has been shown to be important for both horizontal and vertical propulsion (Carr, 1992, Carr and Gentile, 1994). Specifically, the coordination of shoulder flexion and lower limb extension contributes to vertical propulsion and the extent of arm movement has been found to influence force production in the lower limbs during the sit-to-stand (Carr, 1992).

The use of upper body strength for assistance during the sit-to-stand, e.g., when armrests are held for support and assistance, increases the BOS and improves stability (Bahrami et al., 2000, Schultz et al., 1992). Armrest assistance has been suggested to aid in propelling body weight forward, allowing the development of a similar horizontal force to that provided by the forward momentum of the trunk, which is utilised when rising unassisted (Kralj et al., 1990, Schultz et al., 1992). Chair armrests have been found to assist rising from a chair in a number of studies (Alexander et al., 1991, Arborelius et al., 1992, Bahrami et al., 2000, Burdett et al., 1985, Finlay et al., 1983, Schultz et al., 1992, Wheeler et al., 1985).

Older adults who require upper body assistance to successfully achieve sit-to-stand performance adopt a different transfer strategy to able-bodied older aged and young adults (Alexander et al., 1991). Alexander and colleagues found less able-bodied older adults transfer greater force through armrests, take longer time to rise, display less thigh extension and greater trunk flexion. These kinetic and kinematic changes suggest considerable alteration to upper and lower body segmental coordination, which is a critical element of sit-to-stand performance success (Carr, 1992, Linden et al., 1994, Pai and Rogers, 1990, Vansant, 1992). In addition, arm rest use by able-bodied older aged adults during the sit-to-stand reduces trunk and leg flexion without alteration to thigh extension (Alexander et al., 1991). Armrest usage can provide mechanical advantages during the sit-to-stand by decreasing hip and knee moments (Rodosky et al., 1989, Seedhom and Terayama, 1976), however this comes at the cost of increased mean ankle and shoulder moments (Schultz et al., 1992).

When using armrests for assistance at seat lift-off during the sit-to-stand, older adults place a priority on stability rather than a reduction in joint moment requirements (Schultz et al., 1992). This is achieved by positioning the centre of pressure more anteriorly through greater rotation of the upper body segments, thighs and legs. At this moment, a predominantly vertical load is applied to the armrests, a push up rather than a push forward (Anglin & Wyss, 2000). This strategy develops low horizontal momentum making it easier to control the location of the centre of mass (COM) over the BOS, which promotes stability. It is unclear whether optimal arm rest location is determined by an absolute height or a relative height to the individual’s height or arm length (Wheeler et al., 1985).

Analysis of lateral kinetics (Gilleard et al., 2001, Hesse et al., 1996, Hirschfeld et al., 1999, Lee et al., 1997) and three-dimensional motion during the sit-to-stand have been performed by only a small number of authors (Baer and Ashburn, 1995, Gilleard et al., 2001, Kaya et al., 1998, Krebs et al., 1992, Schenkman et al., 1990). Many studies perform sagittal plane analysis and assume symmetry during the sit-to-stand, however only one study has investigated the validity of this assumption (Lundin, Grabiner, & Jahnigen, 1995). The results from that study indicate that assuming symmetry underestimates lower body peak net joint moments.

Compared with armrests, grab rails are positioned further from the seat and closer to the final, upright standing position. It is expected that to achieve assistance from a laterally placed grab rail an alternative sit-to-stand strategy would be necessary to that developed for chair armrests. The strategies developed to obtain assistance from a grab rail are unknown. One could speculate that an anterior and upward grab rail reaction force would assist in the forward and upward movement of the user’s COM and that a laterally placed grab rail would introduce asymmetries into the dynamics. An understanding of these interactions will allow the optimisation of design to increase the effectiveness of grab rail assistance for older aged adults. To fill this gap in the sit-to-stand literature, a quantitative description of grab rail design and sit-to-stand performance is the aim of this study. To follow a rational basis for providing this information, assessment of the positions and orientations that are presented in the standards literature were selected for analysis. The effect of using a grab rail on lower limb muscular effort, as measured by net joint moments and joint powers, and on balance, as measured by body segment motion and whole body COM motion relative to the location of the BOS will be investigated.

The above background leads to the following hypotheses. Firstly, grab rail reaction forces will aid vertical and horizontal propulsion. Secondly, compared with unassisted sit-to-stand, hip and knee net joint moments will be less when using a grab rail for assistance. Thirdly, the effect of unilateral assistance on net joint moments will be asymmetrical. Fourthly, unilateral grab rail assistance will influence body segment movement patterns and dynamic balance during the sit-to-stand transfer.

Section snippets

Methods

The study design was a 2 × 5 factorial multivariate analysis of variance with repeated measures. The factor, Assistance, consisted of unassisted and unilateral assistance, while the other factor, Trials, consisted of five trials. Twelve older aged adults, five males and seven females, volunteered to participate in this study. All participants provided informed consent and the protocol was approved by The University of Sydney Human Ethics Committee. The participants’ age ranged from 69 to 88

Results

The introduction of grab rail assistance did not influence time to complete 100% of the sit-to-stand cycle (F(1, 5) = 1.02, p = .36, η2 = .17). The mean time to complete the unassisted sit-to-stand cycle was 0.63 ± 0.03 s and between 0.61 ± 0.03 s (horizontal, 0.15 m forward) to 0.66 ± 0.04 s (horizontal 0.4 m forward) when assisted. During assistance, the unilateral grab rail was consistently pulled in a medial, downward and posterior directed manner, see Fig. 1. In response, the lateral grab rail reaction

Discussion

This study investigates bilateral three-dimensional kinetic and kinematic responses during the unilateral grab rail assisted sit-to-stand transfer of older aged adults. The unilateral nature of the assistance achieved with a grab rail saw the development of systematic asymmetries in sagittal plane joint kinetics in response to unilateral external reaction forces. Net moments and powers at the knee and hip joints that were relatively symmetrical when unassisted became asymmetric during

Conclusions

In this sample of older aged adults, unilateral grab rail assistance has produced systematic asymmetric changes to net joint moments and powers. However, overall bilateral or unilateral reductions to lower body net joint moments or powers were not produced during unilateral grab rail assistance. A bilateral analysis has been essential to reveal these asymmetric changes. Unilateral grab rail assistance has not altered the angular movement patterns of the trunk or lower body segments during

Acknowledgements

The authors acknowledge the contributions of Ray Patton, Laboratory Manager for the School of Exercise and Sport Science, Faculty of Health Science, The University of Sydney, A&M Henry Pty. Ltd. for its contribution of materials and financial support, and the Australian Research Council, for financially supporting this project.

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