Throwing Yourself into It

Were the weights held by Greek long jumpers a help or a hindrance?

Story by Adam Summers   ~  Illustrations by Patricia J. Wynne

At the Summer Olympics of 1968, in the dry, thin air of Mexico City, Bob Beamon redefined the limits of human performance. The altitude of the venue had led many sportswriters to speculate that records would fall, and the long-jump record was certainly in jeopardy. Jesse Owens's mark of 26 feet 8.5 inches had finally been surpassed in 1960 after having stood for twenty-five years; in the ensuing eight years it had been pushed eight inches. But no one was expecting what was to come. In the Mexico City long-jump finals, in a transcendent display of physical coordination, Beamon jumped twenty-two inches farther than anyone ever had. At 29 feet 2.5 inches it remains the Olympic record, the oldest one still standing; even now, thirty-five years later, the long-jump world record is just two inches greater.

Given Beamon's achievement, it seems ludicrous to say he could have done even better. But a new study of Olympic long jumping suggests that if he had been carrying a gallon jug of milk in each hand, he might still have the world record today.

Alberto Minetti, a biomechanist at Manchester Metropolitan University in Alsager, England, is fascinated with human locomotion. He has explained why small children like to skip but adults don't, how toddlers toddle, and what a strolling gait would look like on another planet. Now, with his colleague Luca Ardigó, he has turned his attention to the role of ancient Greek sporting equipment. In the process he has unraveled a minor archaeological puzzle.

Records of the eighteenth Greek Olympiad, held on the plain of Olympia in the city-state of Elis in 708 B.C., are preserved as detailed paintings on the sides of vases. Documented in some of the sporting scenes are athletes holding peculiar stone or lead implements called halteres. The function of these implements had never been entirely clear. From the paintings on the vases, archaeologists had gathered that in the standing long jump (not to be confused with the running long jump, for which Beamon is celebrated), the athlete would hold one haltere in each hand. During takeoff, he (the ancient Olympics were not co-ed affairs) would swing them both forward; then, while landing, he would swing them back behind his body. But were the halteres carried to encumber, and thus handicap, the best athletes? Or were they, somehow, performance enhancers? Minetti and Ardigó, working with mathematical models and measures of jumping performance, have found that the latter is the case.

The distance covered in any jump depends on three factors: the angle and the velocity of the takeoff and the starting point of the jumper's center of mass. Although handheld weights don't increase the jumper's velocity (indeed, intuitively one would think they had the opposite effect) or change the launch angle, they do affect the center of mass.

Consider our depiction of an ancient jumper moving his arms [see illustration above]. As the athlete swung his arms forward, his center of mass would move forward and upward before his feet had even left the ground. In effect, the jumper gained the advantage of leaping from a slightly higher position, set a little past the takeoff line. As the jumper then came in for a landing, he would swing his arms backward. That motion did nothing to change the trajectory of his center of mass, which traced a parabola as the jumper moved through the air. But it did enable the athlete to push his feet farther out in front of his center of mass than he could without the halteres. As long as the extra weight hadn't slowed his takeoff, that push would have enabled him to go farther, much as if he had swung over a fence and, at just the right moment, pushed off the top rail.

In spite of all the swinging and weight-shifting, the extra weight might still seem an obstacle for a jumper. After all, the kinetic energy of any object-a jumper included-is equal to half its mass multiplied by the square of its velocity. It might seem that adding mass would reduce takeoff velocity, and, that because of the squared velocity, such a trade-off would be far less efficient for the jumper. Yet there is good reason to suppose that takeoff power might actually increase with increasing weight-at least within limits. The more slowly muscles contract, the more force they are able to deliver, which is why heavy weights can only be lifted slowly. Perhaps with some small increase in weight, Minetti and Ardigó reasoned, the added force of the muscle would actually generate more power, leading to an increase in jump distance.

Using a computer model of a jumper, the two investigators determined that adding between eight and fifteen pounds of weight did increase takeoff velocity. Heavier weights than those offset the increase in muscle force, leading to takeoff velocities either equal to or slower than those of an unburdened jumper. The model predicts improvements in jumpers' launch velocities of about 2 percent-an enormous gain in performance at elite levels of competition.

The predictions of computer models are often more compelling than the empirical results with living, breathing (and misbehaving) human beings. But in this case quite the opposite is true. People untrained in long jumping were asked to select a set of randomly weighted halteres, and then to jump while swinging their arms from a platform that measured takeoff forces. Jumpers carrying weights ranging from two to about twenty pounds managed to increase their takeoff power by more than 5 percent. Minetti and Ardigó attributed the improvement over the computer model to the energy-storing effect of the body's elastic tissues: tendons, ligaments, and muscles. Such tissues stretch like rubber bands when loaded. When the jumper takes off, they spring back and return the energy to the jumper.

Such a small increase in power may not seem like much, but even for the untrained jumpers of the experiment, it would add seven inches or so to a ten-foot standing long jump. The last time the standing jump was an Olympic event, at the 1912 games in Stockholm, the three medal-winning jumps were separated by less than four inches; the winner leapt just over eleven feet. Assuming a modern long jumper could master the awkward matter of swinging both hands together during a running start, a similar gain would add about a foot to the distance. Perhaps Mike Powell, the current world-record holder, would be interested in coming out of retirement to try out a well-used set of stone hand weights.

Adam Summers (asummers@uci.edu) is an assistant professor of ecology and evolutionary biology at the University of California, Irvine.