Award details

The sensory role of muscle for the control of balance

Reference	BB/L02103X/1
Principal Investigator / Supervisor	Dr Raymond Reynolds
Co-Investigators / Co-Supervisors
Institution	University of Birmingham
Department	Sport, Exercise & Rehabilitation Science
Funding type	Research
Value (£)	326,131
Status	Completed
Type	Research Grant
Start date	06/11/2014
End date	26/06/2018
Duration	44 months

Abstract

It is well established that sensory information from the ankle muscles is crucial for balance. However, this information is potentially ambiguous because changes in muscle length do not directly reflect changes in ankle angle, and therefore body sway. The ambiguity of proprioceptive information is affected by the mechanical environment of the muscle, including ankle stiffness and muscle strength. We will establish how these factors affect the fidelity with which the ankle musculature tracks ankle angle, and determine the consequences for proprioceptive sensation and postural stability. In particular, we will investigate how these factors change with age. The triceps surae muscles will be measured using dynamic ultrasound during quiet stance. Image analysis will track the changes in muscle length, and this will be correlated with ankle angle. The extent of ankle-to-muscle coupling will be related to ankle stiffness and postural sway. We will also directly test the extent to which this coupling affects proprioceptive sensation at the ankle joint during a perceptual threshold task. Older adults (aged 65-85) will be compared to the young (aged 18-40), to determine how age-related changes in ankle stiffness and muscle strength affect proprioception and postural sway. In addition, we will examine the effect of artificially altering physiological parameters upon postural sway (strength, stiffness, sensory gain) using a 'fictive' standing paradigm. This will involve real-time processing of EMG signals to balance an inverted pendulum. This technique will allow us to examine the effect of changing muscle/ankle properties upon proprioception and sway, both within- and between-subjects. Specifically, we will be able to mimic the ageing phenotype in younger adults, and artificially improve function in older adults. This combined approach will provide us with a comprehensive picture of the mechanisms underlying proprioceptive control of balance, and why it degrades with age.

Summary

Falls are a major problem for older adults, with 30% of people aged over 65 experiencing 1 or more falls per year, rising to 50% in the over 85's. The reasons for falling are multi-factorial, and include problems with both sensation and movement. One of the most important types of sensory input for balance comes from the calf muscles in the lower leg, termed 'proprioception'. There is evidence to suggest that loss of proprioception in older adults may be a key cause of postural instability. However, muscles must produce movement as well as act as sensory organs. Ongoing muscle contraction may therefore affect the ability of muscle to act as a sensor. This, in turn, is affected by individual variations in ankle stiffness, and overall muscle strength. It is well established that these factors change with age, and this may therefore degrade the ability of the muscle to detect body movement. We will test this hypothesis by measuring proprioceptive control of balance in older adults (aged 65-85). Initially, we will examine balance in younger volunteers (aged 18-40) to establish baseline performance. In particular, we will determine how natural variations in ankle stiffness and muscle strength affect the quality of sensory information emanating from the calf muscles during quiet standing. To assess the quality of proprioceptive information in each volunteer, we will use ultrasound to measure calf muscle movement to see how well muscle length tracks body sway when standing. This will be correlated with postural stability. We will then determine how mechanical factors such as ankle stiffness and ankle strength affect this relationship. Furthermore, we will test the influence of these factors upon the ability of subjects to detect very small rotations at the ankle joint. Using an innovative 'virtual' standing paradigm, we will then artificially manipulate strength and ankle stiffness to mimic the ageing phenotype in the young. Once we have established baseline performancein the young, we will study older adults to determine how the well-established musculoskeletal changes affect proprioceptive control of sway. Using the same virtual standing paradigm, we will test the effect of artificially improving function. The strength of our approach is that we can compare proprioception between groups (young vs old) as well as manipulate the above factors within subjects. This combined approach will give us a comprehensive picture of how proprioceptive information is used to control balance, both in the young and aged state. By revealing the mechanisms by which sensory information is used for balance, we will better understand how these mechanisms degrade with age leading to postural instability. This will be of benefit both in being able to better identify those at risk of falling, and being able to tailor specific therapies to improve balance function.

Impact Summary

Our research is aimed at understanding the role of ankle stiffness and muscle strength in the proprioceptive control of balance, and how this is affected by age. This will establish the contribution of lower limb strength and mechanics to postural stability and fall risk in older adults. The work has relevance for those at risk of falling, and clinicians who care for them. Specific groups include: - Older adults will benefit from this research by learning about factors which increase their risk of falling, and potentially by enrolling on appropriate rehabilitation programmes. - Clinicians will benefit from being better able to identify those at high fall risk, and recommending appropriate therapies or exercise programmes. This group includes geriatricians, neurologists, ENT consultants, physiotherapists and occupational therapists. We have a good track record of engaging all these groups to inform them of our previous and planned work in the area of balance and falls. In order to facilitate impact we will organise a series of open days and talks for the lay public, as well as a symposium aimed at professionals: 1. Winterbourne Botanical Gardens Annual Open Day: This meeting engages older adults who are interested in learning about ongoing ageing research at the university, and in volunteering to participate. We will set up a stall at this meeting where the general public can discuss the purpose of our research and volunteer if they wish. 2. Departmental Open Days: Older adults from the general public will be invited to attend two departmental open days. The first will be performed prior to the recruitment of older adults. It will include a general talk on fall risk, as well as our previous research and planned future research, presented in lay terms. It will also include a tour of our laboratories. Key stakeholders will also be invited, including local representatives of the National Osteoporosis Society and The University of the Third Age. Following recruitment of older adults a second open day will be run to present our preliminary findings. We will separately organise a talk to be delivered to the Science Awareness Group of the local University of The Third Age. 3. Balance and Falls in Older Adults - One day professional symposium: This will include national and international invited experts who will present their research findings, in addition to us presenting our research. The invited audience will be a mix of the clinical groups mentioned above. Having recently run a similar symposium, Dr Reynolds has a considerable distribution list to target the most relevant clinicians. In addition to the above activities, we will set up a web page to disseminate our ongoing findings.

Committee	Research Committee A (Animal disease, health and welfare)
Research Topics	Ageing
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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