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74 m a s s a g e & b o d y wo r k m a rc h /a p r i l 2 0 2 3 British statistician George E. P. Box is famous for saying "All models are wrong, but some are useful." In the world of biomechanics, many of our models go all the way back to Giovanni Alfonso Borelli, who, for historical context, died on New Year's Eve, 1679. Borelli was a polyglot, as interested in predicting the orbit of Jupiter's moons as identifying the center of gravity of the human body. For the record, he was quite accurate with the former and not so much with the latter. Borelli's experiments involved placing a supine body on a seesaw of sorts and moving it about until both the board and human achieved balance over the fulcrum. Based on this, he concluded the center of gravity of the body as being slightly below the pubis. While it is now a given that our center of gravity is at approximately 56 percent of our height when measured from the soles of our feet (slightly less than an inch [2.4 centimeters] south of the navel), that's still a pretty good calculation for an inquisitive mind who died eight years before Newton published Principia Mathematica Naturalis, the tome that became the foundation of physics as we know it. Despite that error, Borelli is considered the father of biomechanics and best known for his interpretation of the musculoskeletal system as a series of interconnected levers that magnify motion rather than force. That's a useful model, but what happens to your wrist when you're doing biceps curls with 5-pound weights? Or benching 200 pounds? To account for this, Borelli performed numerous anatomical studies and posited a system of pulleys along the muscles of the forearm to account for being able to hold a weighted object with an extended arm. A MORE ACCURATE MODEL The model of the elbow joint as a lever and the arm muscles as pulleys was useful for its time and is still used today as a default model in many texts and journals. But it's also kind of wrong. If your arm is extended and you're holding a weight, or a phone, or a baby, what exactly are those forearm muscles pulling against, given the horizontality of it all? There are a few particulars this model fails to consider. One is the sheer number of muscles in the arm that cross both the wrist and elbow joints. Functionally, one has to think of them as working in relationship to each other. Then there's the complexity of the wrist itself. Take a moment to f lex your elbow. Now take your wrist through a range of motion. Slowly rotate, f lex, extend, pronate, 74 m a s s a g e & b o d y wo r k m a rc h /a p r i l 2 0 2 3 Tensegrity and Biotensegrity Exploring Interconnectivity Within the Body By David Lesondak critical thinking | BODY OF WONDER

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