Abstract
Background: Senescence of the musculoskeletal system is characterised by declines in muscle strength, muscle mass and physical function. These changes that accompany the ageing process were conceptualised into the condition known as sarcopenia, which is associated with adverse health outcomes and affects over 70% of older adults. Sarcopenia has been recently recognised as a geriatric syndrome; migrating from its original gerontological concept. As the proportion of older adults continues to rise across the world, sarcopenia presents an ever-increasing major health concern and socioeconomic burden. The research to date predominantly focuses on the appendicular muscles, despite the recognised importance of the lumbar musculature in maintaining physical function and independence in older age. Indeed, some researchers have suggested that the lumbar paravertebral muscles (LPMs) may be more susceptible to the effects of age-related sarcopenia than the appendicular muscles, although mechanisms for this phenomenon are ambiguous. With renewed interest, researchers are increasing efforts to understand sarcopenia of the spine which has led to the emerging concept of “spinal sarcopenia”. Given the lack of research on this topic, it is of prime importance to investigate the effects of ageing on muscle morphology, strength and biomechanical function in the lumbar spine. Furthermore, it is important to understand the normal progression of age-related changes in this region to allow identification of sarcopenic and pathological deviations. Therefore, research should initially target healthy adults as undetermined phenotypes are likely hidden in the demographics of general populations. Extending our understanding of age-related changes in the LPMs will also provide guidance for effective clinical and public health intervention strategies to offset adverse health outcomes related to spinal sarcopenia in older adult populations.Aim: The main aim of the thesis was to explore age-related differences in lumbar spine specific measures of sarcopenia (i.e. muscle morphology, strength and biomechanical function) in healthy younger and older men. The secondary aim was to evaluate the interrelationships between muscle morphology, strength and biomechanical function in the lumbar spine alongside differences as a result of age.
Methods: A range of methods was used due to the multidisciplinary nature of the research. Initially, a systematic review with meta-analysis was conducted to establish the relationship between ageing and degeneration of the lumbar musculature. Findings from the meta-regression were also used to inform methodological decisions regarding investigation of LPM morphology. Subsequently, quantitative MRI was performed to evaluate age-related volumetric and compositional differences in the LPMs. This study was the first of three prospective observational studies to obtain primary data. Twelve healthy older men (67.3 ± 6.0 years) and 12 healthy younger men (24.7 ± 3.1 years) were included. Participants in the young group (YG) were matched to participants in the older group (OG) based on sex, ethnicity and physical activity (PA) level. To obtain strength data specific to the lumbar spine musculature, isokinetic dynamometry was applied to the trunk in the second experimental study. The OG and YG completed a protocol which included concentric and eccentric contractile modes as well as a wide range of angular velocities (15°·s-1 to 180°·s-1). Finally, age-related differences in biomechanical function of the trunk during walking gait was explored using 3-D motion analysis. Statistical parametric mapping was used as a novel approach to determine phase-specific differences in kinematic and kinetic waveforms between the young and older age groups. As muscle measures are sensitive to lifestyle factors and health status, confounding variables such as PA level and physical disability were measured and controlled for where appropriate.
Results: From the 34 studies (n = 6047) included in the meta-analysis, ageing was associated with atrophy (r = -0.255) and fat infiltration (r = 0.394) in the lumbar musculature. These degenerative changes also showed muscle, lumbar level and sex-specific responses. It was recommended that studies should use high-resolution imaging modalities to measure muscle volume across levels and across all muscles in the lumbar spine. Subsequently, the T2-weighted axial MRI images of the lumbar spine showed that increased fat infiltration was a global change across the lumbar musculature in older age. However, atrophy was muscle specific with age explaining 42% and 18% of the variance in quadratus lumborum and erector spinae muscle atrophy, respectively. Interestingly, PA level did not moderate the effect of age on muscle morphology degeneration (i.e. atrophy and fat infiltration). Concentric strength of the back muscles declined with age, which was more pronounced at greater movement speeds. However, loss of muscle volume and increase in fat infiltration was not able to explain age-related concentric strength loss in the trunk extensor muscles. It was likely that neuropathic processes with ageing were the cause of reduced concentric extensor strength in the OG. There was also an apparent preservation of eccentric trunk strength in older age, which was negatively associated with quadratus lumborum fat infiltration but not age. Regarding biomechanical function of the trunk during walking, the OG demonstrated reduced movement amplitudes in all planes of motion. However, reduced trunk movements in the coronal plane were likely a reflection of decreased range of pelvic obliquity motion. Few differences existed in trunk kinetics between the YG and OG, although the YG performed significantly more negative work in the coronal plane during the gait cycle (GC). This was likely due to greater lateral flexion excursions. Walking was on average 20% more functionally demanding on the trunk muscles in the OG compared to the YG, although this difference was not statistically significant. There was also evidence of interplanar uncoupling of trunk motion in older age, which may increase the energetic demand of walking. Loss of muscle volume and increase in fat infiltration was unable to explain age-related differences in biomechanical trunk function.
Conclusion: This thesis represents the first research to investigate lumbar spine specific measures of age-related sarcopenia. The dataset will provide a useful step in establishing normal features of muscle degeneration, strength loss and functional decline in the lumbar spine with ageing. This thesis will also help to establish the concept of spinal sarcopenia, which is an emerging field of interest in healthy ageing and musculoskeletal research. Furthermore, the findings within this thesis can be used in future research to design more effective targeted interventions aiming to improve physical function and health outcomes in older adults.
| Date of Award | Jul 2021 |
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| Original language | English |
| Awarding Institution |
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| Sponsors | Coventry University & University Hospitals Coventry and Warwickshire NHS Trust |
| Supervisor | Michael Duncan (Supervisor), Derek Renshaw (Supervisor), John Hattersley (Supervisor) & Jason Tallis (Supervisor) |