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Title: Quantifying musculoskeletal reserve in the elderly
Author: Smith, Samuel
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2018
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Developments in modern medicine, promotion of well-being in the elderly, and a greater understanding of healthy lifestyles have all culminated in our current 'ageing population'. It is predicted that by 2050 the population of over 65s will be 20% of the estimated general population. Most ageing research recognises that the ageing population has repercussions for both the economy and healthcare systems, however, this research fails to address the consequences of physiological changes in this ageing population. Our bodies are not designed to perform at high levels of activity past certain ages. Muscle mass begins to decline around the 5th decade with diminishing internal systems, making activities which were easier at a younger age more strenuous on the body in later life. 'Musculoskeletal Reserve' (MSKR) is the concept of a reduced strength capacity in response to external stressor events, which is of greater relevance in the injured or severely frail. MSKR is quantifiable, and therefore can be used in conjunction with tools such as musculoskeletal modelling in approaching the problem of declining functional ability. The movements of 95 eighteen to ninety-five year-olds were measured during a sit-to-stand task to better understand how the current elderly population is adapting to a lack of MSKR. This research was achieved through collaboration with the Royal Hospital Chelsea. This group had a significantly different muscle recruitment strategy when compared to the young group, which may have been protecting vulnerable joints. The younger group used contraction of the quadriceps to lift their body to stability from a quasi-static position after leaving the seat. The elderly subjects had much lower quadriceps forces, thus lowering the forces on the knee joint, and compensated by increasing the activity of the hamstring and calf muscles as an alternative in reaching the final standing position. The action of these compensatory muscle groups is less naturally efficient than those of the quadriceps, and despite significant decreases in joint force, places larger forces on muscles not usually recruited for such activities. The changes in muscle recruitment were found to be subject to an alteration in movement strategy. The young made use of fast, tetanic contraction of the quadriceps to lift the body, whereas the elderly used prolonged activity of the alternative muscle groups listed above to stand from a seated position. This shift from acceleration to muscle effort makes simple, everyday activities more strenuous on the body. More importantly, it reduces the MSKR which constitutes the body's ability to overcome the external stressors of injury or MSK-related disease. Therefore, injury of any compensatory muscle will cause functional decline. This was most profound when rising without the assistance of arm-rest support, which when used would dramatically increase elderly joint forces in the shoulder when compared with the young; a potential intervention in shoulder postural position at the start of motion may reduce joint forces in this task. A premature reduction in lower limb strength with age places more reliance on the upper limb muscles to complete everyday activities, resulting in further lower limb atrophy through disuse. The eventual decline of upper limb strength leaves the elderly with a lack of MSKR to complete the activities, leading to increased vulnerability, dependence on others and risk of institutionalisation.
Supervisor: Bull, Anthony Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral