Abstract

Although bone loss is an inevitable part of ageing, effective preventive measures and positive health practices, including sufficient calcium intake and adequate physical activity, applied across the lifespan can delay or prevent the onset of osteoporosis. Regular exercise in particular has been found to positively correlate with gains in bone mineral density in young adults and with reductions in the rate of bone loss in older adults. Bone is a dynamic tissue, which responds to various signals, including chemical, mechanical, electrical, and magnetic stimuli. Exercise increases the mechanical loading applied to the bone through muscle contraction forces, while with high-impact activities additional loading is applied through ground reaction forces. The effects of exercise on bone biochemistry have been studied through the measurement of changes in the circulating levels of bone turnover markers (BTMs). BTMs are biochemical metabolites derived from cellular and non-cellular compartments of bone during the bone remodelling process. A popular marker of bone formation is PINP and of bone resorption is CTX, which are specific markers of type I collagen formation and degradation, respectively. Although there is inconsistency regarding the effects of acute resistance exercise, aerobic exercise, and plyometric exercise on BTMs, the general trend is for bone formation markers to remain unchanged and bone resorption markers to decrease. These inconsistencies are why no one particular exercise regimen is recommended above others for the mitigation of osteoporosis. In fact, walking continues to be the simplest, safest, and more economic exercise recommendation for older adults, while plyometrics should remain part of the exercise recommendations for younger populations. Studies have also measured circulating levels of osteokines, which are bone-derived cytokines that are produced by bone cells to regulate the metabolic activity of bone via specific signalling pathways. The most well-known osteokines measured in human serum are sclerostin, osteoprotegerin (OPG), and the receptor activator of nuclear factor kappa B ligand (RANKL). Exercise training has been shown to decrease bone resorption through changes in the RANK/RANKL pathway, but the results are age and sex dependent. Other factors, including energy availability, calcium stores, and oestrogen, may influence the bone adaptation to exercise, although more research is needed to shed light on these effects and the cellular mechanisms associated with bone turnover.