Abstract
According to the figures calculated from the photogrammetric data of take-off in running high jump, the mechanical energy (potential energy plus kinetic energy) of the center of gravity of the body and the distance from the center of gravity of the body to the contacting point of the take-off foot with the ground ("s"), when plotted against time, showed concaved curves in which the minimum values were reached at about 0.05 to 0.07 sec. after the contact of the take-off foot with the ground. The smoothed curve of ground reaction (F^^-s) recorded by the forceplate showed a convexed curve with its maximum at about 0.05 to 0.07 sec. It was possible to interpret the relationship among these changes by the model of spring-mass system in which the center of gravity of the body is connected by a spring to the contacting point of the take-off foot with the ground. In order to satisfy the condition that the spring constant of the model used in this study is positive and the model is to keep the physical effectiveness, "s" must be smoothed so that the time of its minimal value coincide with the time of the maximal value of F^^-s. The correlations between the height of the bar cleared and each of the spring constant, the proper period of the model and the take-off time were not significant. However, in most of the cases, the significant correlation was observed between the height cleared and the "take-off ratio" (the ratio of the take-off time to the proper period of the model) of the same subject. In accordance with the rise of height cleared, some subjects showed a decreasing pattern of the "take-off ratio," while the others showed an increasing pattern. In case of the subject whose record reached 2.20m, a highly significant positive correlation (r =0.968) was observed between the height cleared and the take-off ratio. For the height above 1.90m, the take-off ratios of this particular subject (0.303-0.331) were larger than those (0.248-0.313) of the three other subjects whose best record reached only to 2.00m.
