New York: Researchers have found that injecting a hormone secreted by bones can help the ageing muscles become youthful as well as increase the capacity of exercise in the elderly, finds a new study. Osteocalcin, a bone hormone produced during exercise, tends to decline with age in women at the age of 30 and in men at age 50. The findings showed that during exercise in mice and humans, the level of osteocalcin in the blood increases depending on how old the organism is. Osteocalcin increased the capacity of exercise in the older mice. Also, the bone-derived hormone was found powerful enough to reconstitute, in older animals, the muscle function of young animals. "Our bones are making a hormone called osteocalcin that provides an explanation for why we can exercise," said Gerard Karsenty, Geneticist at the Columbia University Medical Center in the US. For the study, published in the journal Cell Metabolism, the team tested mice that were genetically engineered to investigate whether osteocalcin levels were affecting exercise performance. In three-month-old adult mice, osteocalcin levels spiked approximately four times the amount that the levels in 12-month-old mice did when the rodents ran for 40 minutes on a treadmill. The three-month-old mice could run for about 1,200 meters before becoming exhausted, while the 12-month-old mice could only run half of that distance. However, when old mice whose osteocalcin levels had naturally decreased with age were injected with osteocalcin, their running performance matched that of the healthy three-month-old mice. The older mice were able to run about 1,200 meters before becoming exhausted. "Osteocalcin is the only known bone-derived hormone that increases exercise capacity. This may be one way to treat age-related decline in muscle function in humans," Karsenty noted.