I am hanging by one arm from the branch of a tree, my bare toes clawing into the gnarled bark of its trunk. “Try swaying your body,” shouts fitness trainer Colin Holding from several feet below. Sway? Were I to move so much as my little finger, I fear I will lose my grip and land in ungainly fashion at his feet. Muscles contorting with effort, I cling on until Holding instructs me to “walk” my way back down the tree before letting go. But we are not done. There are bushes to be scooted under on all fours, boulders to be leapt over and logs to be hauled. Holding is one of the UK’s leading instructors in evolutionary fitness, an approach to exercise that aims to reintroduce the natural movement patterns — crawling, jumping, lifting and climbing — that kept our ancestors strong and agile before the advent of plush gyms and yoga studios. The idea is simple: turn nature into your fitness emporium by using stones as dumbbells, branches as pull-up bars and logs as steppers. Five years ago the concept of crawling through leaves and squatting like a gorilla might have seemed an inconceivable alternative to a bootcamp class. But a growing anti-gym sentiment among people who have become bored with “sterile” training environments is fuelling demand for more natural, organic workouts taught by instructors such as Holding. Read on at The Times