Tarzan right to swing through jungle To compare the energy required to sway trees, climb trees, or jump from branch to branch, Dr Lewis Halsey's team created obstacle courses simulating these activities. But instead of orangutans, the participants were parkour athletes, specially trained street gymnasts with good flexibility and spatial awareness. They wore devices that recorded their oxygen consumption as they proceeded through the activities. Dr Halsey says the findings help explain why the orangutans spend so much time in the treetops - and why heavier orangutans, for whom swaying the branches comes more easily, don't leap. He said: "Heavier orangutans don't jump, and we may have an explanation why." Because their diet of fruit does not provide much energy efficiency it is vital for the primates, said Dr Halsey. He said: "Energy expenditure could be a key constraint for orangutans - moving through trees could be energetically expensive. Because primates are not easy to work with, estimates of energy expenditure have been very indirect. We have gone a step closer to understanding these costs by measuring energy expenditure in a model primate - the parkour athlete.