Profitable Wonders
Human athletic prowess, it might seem, is a puny thing compared with that of our fellow creatures. Usain Bolt’s blistering 27.8mph world record is trumped by the humble warthog (30mph when cruising). Australian swimmer Eamon Sullivan’s 100m freestyle speed of 4mph is far eclipsed by the black marlin (80mph). Paul Anderson, reputedly the world’s strongest man, able to carry eight people on his back, is a mere stripling (in relative terms) compared with the horned dung beetle that can pull a thousand times its own body weight.
Still, those superstars of the animal world are specialists, excelling in one domain, whereas we humans are generalists who can run and jump and swim and throw the javelin. Only humans can surf or roller skate or play football or make a free ascent of the most challenging rock climb in the world – the 3,000ft, sheer, vertical cliff face of El Capitan in the Yosemite National Park. Only humans, like the fourteen-year-old Romanian Nadia Comaneci, could score seven ‘perfect 10s’ on the uneven bars and vault in the 1976 Montreal Olympics.
‘She saluted the judges and ran towards the apparatus,’ writes former gymnast Dvora Meyers, ‘jumped on the springboard to vault herself over the low bar and grab the high rail, casting up to a handstand, a straight vertical line all the way from her wrists to her toes. Then she swung down, beating her hips against the low bar, the force of which propelled her body back up on the high rail and into a handstand once again.’
That perfection, as awesome and exhilarating when viewed now (on Youtube) as forty years ago, could almost be a masterclass in those distinctive attributes of flexibility and control that make possible the astonishing diversity of the human athletic achievement. ‘We are in reality multi-articular machines,’ observed anatomist Sir Arthur Keith. There are 250 joints in all, permitting a near infinite range of combinatory movements.
They fall into five main groups (ball and socket, hinge, ellipsoid, saddle and pivot) but no two are structurally identical, meaning they encompass hundreds of different articulations. The mechanics of each is a ‘triumph of engineering’ but, being so breathtakingly complex, they defy any simple description. Still, comparing variations of a single type helps illuminate that super-flexibility of the human skeleton.
Thus, while the ball and socket of the shoulder and hip allow for the widest possible movement of any type of joint, the specifics of their structure is determined by their purpose – the shoulder to permit the maximal operational range for the hand (‘the major executive organ of the body’), the hip to both propel the limbs and sustain the weight of the body.
The ball and socket of the shoulder is accordingly shallow, allowing the large head of the humerus to variously roll, rotate and slide without impediment against the wide articular surface of the glenoid cavity on the upper, outer tip of the shoulder blade – which, in turn, acts as a moving platform extending the excursion of the arm still further. This arrangement permits a combined range of movement (flexion, extension, adduction and abduction) of an incredible 640 degrees, such that the hand is continuously positioned in the centre of vision in front of the body.
For the hips, by contrast, which must combine locomotion and stability, the rounded head of the femur is embraced in a perfect fit into the socket (or acetabulum) and held in place by powerful supporting ligaments. Thus its range of movement, though still considerable, is less than half that of the shoulder.
The configuration of the functionally most important joints of the hand and foot – the thumb and big toe – is by contrast quite different. That at the base of the thumb is shaped like a rider in a saddle so the tip of the thumb can reach across in opposition to the tip of the index finger. This is the ‘hallmark of mankind’, permitting small objects to be manipulated with unlimited potential for fine adjustments or minute corrections – whether threading a needle or playing the flute. Meanwhile, the big toe equivalent is a simple, rounded, convex surface articulating against a shallow concave cavity. Its relatively limited range of movement permits it to act as a lever impelling the body forward, ‘an elastic, mobile, dynamic organ of propulsion’.
And, finally, the most important joint of all at the base of the skull, which must allow for a sweeping arc of 180 degrees in two directions, while protecting the vital, vulnerable spinal cord. This atlanto-axial joint requires a two-fold adaptation of the conventional vertebral structure: a shallow ball-and-socket joint, allowing the head to nod up and down while a peg of bone, sticking up from the axis beneath, acts as a pivot, around which the head can rotate from side to side. A triumph of engineering indeed!