To Örebro University

Ageing is accompanied by a progressive decline in skeletal muscle mass and strength which may lead to impaired ability to perform activities of daily living in older adults. Although the exact cause of the gradual decline in muscle mass is unknown, identifying efficient strategies aiming to prevent age-related loss of muscle mass and strength is important in order to promote healthy ageing. The overall aim of this thesis was to explore the effects of resistance training alone or combined with a healthy diet on skeletal muscle mass and function of healthy recreationally active older women and to determine mechanisms by which elevated systemic inflammation may contribute to the age-related decline of muscle mass in older adults. The combination of resistance training and a healthy diet induced gains in leg lean mass as well as greater gains in dynamic explosive force than resistance training alone in healthy recreationally active older women. The observed gains in leg lean mass were accompanied by increases in the size of type IIA muscle fibres together with down-regulation in gene expression of a pro-inflammatory factor (IL-1β) and upregulation in gene expression of a regulator of cellular growth (mTOR) in skeletal muscle of older women. Additionally, reduced muscle protein synthesis and size of muscle cells may mediate the detrimental effects of elevated circulating markers of inflammation on muscle mass in older adults. In conclusion, the present thesis depicts mechanistic links between elevated systemic marker of inflammation and muscle mass and provides new information on the effects of combined resistance training and healthy diet on muscle mass and strength in a group of healthy recreationally active older women. This knowledge is instrumental for development of strategies aiming to prevent age-related loss of muscle mass and function.

Ageing is associated with a gradual deterioration in physical function, accompanied by a decrease in muscle mass, leading to loss of independency. In this respect, physical activity and healthy diet represent key lifestyle factors with potential to delay onset of age-related physical disability. The overall aim of the present thesis was to explore the effects of physical activity behaviours in general and resistance training (RT) in particular, with or without addition of a healthy diet (HD), on muscle mass and physical function in older community-dwelling women. A main finding was that physical activity of at least moderate intensity at old age infers beneficial effects on physical function, even in individuals with a previously sedentary lifestyle. Additionally, engagement in exercise-related activities during middleage years is linked to better physical function and higher muscle massat old age, regardless of present physical activity level. This thesis further highlights that in older women RT combined with HD rich in omega-3 polyunsaturated fatty acids elicits significant gains in muscle mass, whereas no corresponding gain was induced by RT alone. Likewise, larger improvements in muscle strength and physical function were evident in response to combined effects by RT and HD compared to RT alone. Taken together, findings from this thesis support public health efforts aiming to promote physical activity of at least moderate intensity together with a healthy diet rich in omega-3 polyunsaturated fatty acids in order to combat age-related decline in muscle mass and physical function.