Muscle sarcopenia and weakness are common health problems accompanying ageing. As the proportion of people older than the age of 60 in our population increases, it becomes important to understand systems implicated in the regulation of muscle strength in ageing. This thesis investigates biochemical changes occurring within skeletal muscles of ageing individuals. A proteomic method of identifying biomarkers was developed and optirnised for discovery and verification of protein biomarkers from small skeletal muscle biopsies from mice. This was an integrated proteomics platform using 2D-DIGE, LC-MS-MS and SELDI-TOF-MS. The method was adapted to find biomarkers from human muscle biopsies. Four human subject groups (10 old females, 5 young females, 4 old males and 7 young males (old: 65-80 years old; young: 20-30 years old» were recruited and completed three-months regime of strength training employing leg press and leg flexion and extension weight training machines. Biopsies from the vastus lateralis (used for isometric strength testing) were taken on day 0 and day 90 of training. An initial screen for differentially expressed proteins between female young/old pre- and post- training was performed using 2D-DIGE (n=3). Muscle ageing in females was associated with significant differential expression of 21 protein biomarkers. 19 of these protein biomarkers were differentially expressed after three months of training were identified, including RKIP/PEBP1. SELDI-TOF was used to study all 52 samples (10 old females, 5 young females, 4 old males and 7 young males pre- and post- trained the three-month strength training). Because of its central role in a number of key intracellular signalling processes including suppressing cancer cell metastasis, RKIP/PEBPI was investigated further. Western blots (n=4) of mouse muscles showed absolute levels of both RKIP/PEBP1 and its phosphorylated isoform (phospho-RKIPfPEBPl) were more highly expressed in slow contracting soleus compared with fast contracting digitorum longus muscles, The relative proportions of phospho-RKIPfPEBPl and total RKIP were the same in both types of muscles suggesting that the balance in the effect of signalling was unchanged. To test that if the increased RKIPfPEBPl in ageing skeletal muscle acts to suppress RAF-l kinase activation of MAPK (ERKl and ERK2) through MAPK/ERK pathway, Western blots assay of ERKl and ERK2 in young and older female's muscle biopsies (n=3) were performed. The results show that they increased proportionately in aging muscles. Thus the increased RKIP/PEBPl in ageing skeletal muscle may not act to suppress RAF-l kinase activation of MAPK (ERKl and ERK2). This implies a different role for RKIPIPEBPl III I skeletal muscle. To test if RKIlPEBPl expression was neurally regulated and if denervation would therefore eradicate RKIP expression, western blot analysis (n=4) was used to assay the levels of total RKIP and phospho-RKIP/PEBPl in soleus muscles of rats following 5 weeks of irreversible muscle denervation. The level of Phospho-RKIP/PEBPl (Ser-153) expression was reduced 2.5-fold but the level of total RKIPIPEBPl was unaffected by irreversible denervation. In summary, it is demonstrated for the first time that both total RKIPIPEBPl and phospho- RKIPIPEBPl (Ser-153) are higher in older muscles than in young muscles pre-training. RKIPIPEBPl may play an important role in modulating skeletal muscle phenotype during ageing.