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Biochemical markers of bone turnover allow inference of the events occurring at the bone tissue level and may detect changes in bone cell activity earlier than densitometric technologies. Serum concentrations of receptor activator for nuclear factor kappa-beta ligand (RANKL), osteoprotegerin (OPG), osteocalcin, and N-telopeptide (NTx) were measured in women aged 20 + 1.5 years (mean + SD) who underwent 32 weeks of unilateral isokinetic concentric or eccentric muscular strength training. Changes in serum biomarkers were compared with changes in arm and leg flexor and extensor muscle strength. Dual X-ray absorptiometry (DXA) measures of bone mineral density (BMD) and bone mineral content (BMC) of the total forearm, total tibia, and total body also were assessed. The mean serum OPG concentration increased from 4.6 + 1.9 pmol/L to 5.2 + 2.1 pmol/L (â 14.9 %, mean + SD; p = 0.05, n = 20) following long-term isokinetic exercise training that also increased elbow extensor and knee flexor muscular strength (p < 0.05) and total forearm BMD (p = 0.04). The ratio of OPG/RANKL also increased over the course of the study (p = 0.045). Serum concentrations of other measured bone biomarkers did not change during training. Serum concentrations of OPG, a suppressor of osteoclastogenesis, increased with high-load muscular strength training that led to local increases in muscle strength and BMD. These adaptations may represent an exercise-mediated suppression of osteoclast differentiation and activity. The central role of the RANKL-OPG cytokine system in the regulation of bone cell biology is well established. Further research is needed to confirm the efficacy of using serum OPG and RANKL as biomarkers of bone cell metabolism in healthy populations undergoing long-term exercise interventions. Master of Science