Why? The Science of Athletics

264 WHY?-THE SCIENCE OF ATHLETICS the push-up should, and does, contribute another I2 to r8 inches. So far as the high jump is concerned, some geometrical considerations in relation to the take-off and landing, as indicating work above the bar, have been given in an earlier chapter. It has been stated as a fundamental principle, moreover, that half the secret of successful high jumping is to be found in the ability of the athlete to get all the heavy parts of his body down to the level of his centre of gravity in effecting bar-clearance. Before the athlete arrives · at that stage, however, he must learn how to raise his centre of gravity to bar level and just how high he needs to raise it for each par– ticular height he is attempting. This information can be obtained by what may be termed "stop-watch calculation", but for timing a high jumper it will be best to use a watch split to hundredths of a second. Professor A. V. Hill, when making tests of this kind, discovered that a man clearing 5 ft. is off the ground for 4/5ths secs., between take-off and landing, and deduces that virtually half of the time is spent going up and the other half coming down, with an infinitesimal fraction of a second spent in "wriggling" over the bar. Perhaps, however, the subject of the experiment was not particularly expert as a high jumper, for the real masters of the art seem to get a distinct pause-period in the execution of their turn-cum-lay-out over the bar. Importance of Timing Field Events Per– formances The time occupied in the jump, how– ever, supplies the basis for the calcu-lation of how high the centre of gravity actually rises. To revert to the analogy of our pole vaulter, by assuming that the man's centre of gravity- is at the middle point of a line passing through the upper ends of his femur, we can say that in the case of the high jumper also it would be approximately 3 ft. above the ground at the instant of take-off, but if the jump occupies 4/5 secs., then the centre of gravity is raised 2 r /2ft., i.e. 6 ins. higher than the height of the cross-bar. But this is unnecessary, if a man jumps