Author:

Abstract:

Due to improvements in lifestyle and healthcare facilities worldwide, people are living longer. Human ageing is associated with neuromuscular adaptations, which can lead to age-related muscle failure or sarcopenia. Muscle power, the product of muscle force and velocity, deteriorates faster with ageing compared to muscle force and is highly related to functional activities such as walking, balance maintenance, standing up from a chair and stair climbing, which makes it crucial for independent living. Therefore, tracing muscle power loss at an early stage can be seen as a key element in the prevention of functional decline with ageing. Traditionally, muscle power of the lower limbs is measured with complex and expensive equipment. However, the use of functional tests like a stair climbing or sit-to-stand test seems better suited for frequent assessments in large-scale practice. Inertial measurement units can be a helpful tool, because they can be used to estimate the vertical power required to elevate the body's center of mass during a sit-to-stand transfer or stairclimbing. Alternative methodologies exist, such as duration-based equations to estimate mean sit-to-stand or stairclimbing power. The main objective of this doctoral thesis was to explore the possibility of commonly used functional tests to contribute to the early detection of functional problems that come with ageing. Furthermore, we want to gain more insights in the role of optimized methodology for measuring lower-limb muscle power (i.e., inertial measurement units and mathematic equations). This with as ultimate goal to make lower-limb power measurements more widely accessible on large-scale basis. Chapter 1 focusses on the ability of various field tests to detect age-related differences across the full adult lifespan. The following tests were assessed: timed up and go, maximal gait speed, handgrip strength, sit-to-stand, stairclimbing and a countermovement jump (article 1). This article shows that the stairclimbing and countermovement jump test are the most sensitive tests to observe age-related differences in physical functioning before the age of 60 years. After the age of 60, all abovementioned tests - except the sit-to-stand test - showed increased sensitivity to detect age-related declines in physical functioning. Although, these declines are most pronounced in the stairclimbing and countermovement jump test. Chapter 2 explores the stairclimbing test. In article 2, it is shown that different power parameters during stairclimbing can be measured reliably and that stairclimbing performance can be distinguished into three phases; an acceleration phase where power is build up, a phase of maximal performance or highest power and a phase of power loss (only measurable in staircases with sufficient number or steps). Furthermore, this article showed that a smaller stair model can be used for measuring SC power reliably in settings where a regular staircase is not available. Article 3 explored potential differences between SC power measured with an IMU and estimated with a mathematic equation. Main findings were that equation-derived power showed lower values compared to sensor-derived power and that the difference between both methodologies enlarged in subjects with better performance. Furthermore, equation-derived power seemed less sensitive to detect age-related changes in physical functioning compared to sensor-derived power. Chapter 3 focusses on the movement phases and power generation during fast sit-to-stand transitions. Article 4 showed that age, sex and functional level have an influence on the movement strategy when standing up from a chair. Weaker subjects spend proportionally less time in the power-generating sit-to-stand phase and proportionally more time in the eccentric stand-to-sit phase. Additionally, limited-functioning older adults spend proportionally more time in the static sit and stand phases compared to well-functioning older adults, resulting in proportionally less time in the dynamic sit-to-stand and stand-to-sit phase. Lastly, trunk flexion during the sit-to-stand phase increase with increasing age and were higher in women compared to men. In young and middle-aged people, the stairclimbing and countermovement test show high sensitivity to detect age-related differences in physical functioning (in contrast to the timed up and go and sit-to stand test which showed less sensitivity, and the handgrip strength and maximal gait speed test which showed no sensitivity to detect age-related differences before the age of 60 years). In older aged people (>60 years), the sensitivity to detect age-related declines in physical functioning increased in almost all tests. Although, these declines are most pronounced in the stairclimbing and countermovement test. Stairclimbing and sit-to-stand power can be measured reliable with an inertial measurement unit and can ben estimated with a duration-based equation. Inertial measurement units measure continuous and give insight in the different sub-phases of the movement. This information is missing when estimating mean power with a duration-based equation. Both methodologies differ and this PhD thesis give insights in the possible (dis)advantages of using them.