Muscle ageing involves structural and functional changes of muscles, mainly their replacement by fatty and fibrous tissue accompanied by the loss of muscle function. Quantitative magnetic resonance imaging (qMRI) methods have potential to provide biomarkers of degenerative changes in muscles with ageing. To assess the relationship between qMRI parameters of lumbar paraspinal muscles (LPMs) and their function and evolution with ageing in healthy subjects, 90 volunteers underwent MRI of lumbar spine and LPM utilising a 6-point Dixon gradient echo sequence. Using manual muscle segmentation, fat fraction (FF) and functional muscle volume (FMV) were calculated for LPM, with the psoas muscle (PS) as a control muscle. Functional parameters of LPM (strength and endurance) were assessed. Based on our data analysis, both FF and FMV of LPM correlate significantly with maximal isometric lumbar extensor muscle strength, but not with endurance. With ageing, FF of LPM increases by 34% per decade, while FF of PS increases by 17% per decade. This difference between LPM and the PS in the rate of FF increase is significant. FMV evinces a decreasing trend in both LPM and PS. However, only FMV of PS decreases significantly by 7% per decade. Our cross-sectional study shows a significant correlation between qMRI parameters of LPM and their strength. FF appears to be a biomarker of muscle ageing with different ageing patterns of distinct muscle groups: LPM and PS.