Why? The Science of Athletics

302 WHY?-THE SCIENCE OF ATHLETICS Propelling Force Provides Mechanical Key to Speed Body propulsion takes the form of two rectangular components, as seen in Diagrams B and E ; of these the horizontal component is the effective force of propulsion, bvt is less than the total applied force if we take the forces as being proportional to the length of the lines which represent them. It will be noted that the propelling force is less at the start of a race (Diagram A) than when the runner is in full stride {Diagram E). Diagram E makes plain, also, the fact that any pronounced kick up of the heel of the rear leg is wasteful, since the vertical component represents waste. Leverage again enters into the discussion, because the strength of the push depends upon the power employed in the extension of the ankle, knee and hip joints, whose leverage functions we have already observed. Some of the effectiveness of the leg drive must, however, be lost, because it operates against the ground at an angle. The means of overcoming this handicap are found in le:;sening the angle by moving forward the runner's centre of gravity. For instance, he increases his propelling force by raising his knees. The forward lift of one knee moves forward the centre of gravity abeut 2 centimetres, and _another centimetre is gained by the forward arm swing. The recovery action of the arm and opposite leg increase the pushing power and also maintain the proper body angle by moving forward the centre ofgravity. Mechanics Solve Problem of Stride Length Another problem that has been solved by the application of mechanical principles to athletics is that of what constitutes proper stride length for different running distances. As long ago as 1836 observations made by the Weber brothers at Gottingep. and Leip– zig postulated that the faster a man runs the longer his stride needs to be, and, no matter what athletes may have thought meanwhile, the photographic experiments in France of Marey, and, coincidentally, the observations of Runar Ohls on Finnish distance ·running, seem to bear