The Functional and Anatomical Impacts of Healthy Muscle Ageing

SIMPLE SUMMARY: Ageing sometimes leads to changes in the size, shape and structure of muscles. This impacts their ability to perform their functions and so leads to an increased likelihood of injuries and negatively impacts quality of life. This work attempts to investigate how the structure and performance of individual muscles of the human leg may change due to ageing, using a combination of magnetic resonance imaging and muscle strength testing in groups of aged (65+ years old) and young (18–40 years old) individuals. The results showed a larger difference in muscle structure and strength in the muscles that extend the knee (i.e., the quadriceps) between the age groups relative to other muscles, and these muscles also showed the strongest relationships between structure and strength. There was also greater variation in fibre lengths and variables linked to fibre type and quality within individual muscles in the aged group compared to the young group. Overall, these results show that even healthy ageing may cause large changes in muscle structure and decreases in performance and that the quadriceps muscles could be a target for exercises to reduce the negative effects of ageing. ABSTRACT: Even “healthy” muscle ageing is often associated with substantial changes in muscle form and function and can lead to increased injury risks and significant negative impacts on quality of life. However, the impacts of healthy muscle ageing on the fibre architecture and microstructure of different muscles and muscle groups throughout the lower limb, and how these are related to their functional capabilities, are not fully understood. Here, a previously established framework of magnetic resonance and diffusion tensor imaging was used to measure the muscle volumes, intramuscular fat, fibre lengths and physiological cross-sectional areas of 12 lower limb muscles in a cohort of healthily aged individuals, which were compared to the same data from a young population. Maximum muscle forces were also measured from an isokinetic dynamometer. The more substantial interpopulation differences in architecture and functional performance were located within the knee extensor muscles, while the aged muscles were also more heterogeneous in muscle fibre type and atrophy. The relationships between architecture and muscle strength were also more significant in the knee extensors compared to other functional groups. These data highlight the importance of the knee extensors as a potential focus for interventions to negate the impacts of muscle ageing.