Biomechanics kicks soccer into relevance for football

— Paradigm shifts in sports fascinate me, in part because they’re virtually always unscientific. Everyone is doing things one way, then a pioneer realizes that another technique simply feels better. While athletes can immediately choose between the old and the new, scientists spend years deciding whether the new technique is truly an advancement.

Consider the Fosbury flop. Before the 1968 Olympics, almost all high jumpers went straight at the bar, throwing one leg and their head over at the same time. When Dick Fosbury came along with his backward, head-first, facing-the-sky technique, Time magazine referred to it as “preposterous.” Even Fosbury’s own coach told the magazine, “I wouldn’t advise anybody else to try it.”

That was right before Fosbury won gold and set an Olympic record. Four years later, most of the competitors used the Fosbury flop. It took researchers years to figure out the physics of why the flop worked so well.

Now that football is in full swing, I’ve been thinking about the scientific explanation for another paradigm shift. Beginning in the 1960s, the “soccer style” of place-kicking began to take over professional football. Younger sports fans might not remember the old straight-on style. The kicker stood directly behind the ball, creating a straight line connecting him, the football and the uprights. The holder placed the ball straight up, perpendicular to the ground. The kicker took a short step, then a full step as he swung his kicking leg straight back, then snapped it forward. His ankle locked, keeping his foot in an extreme flexed position as he walloped the ball with his toes.

Virtually everything about this technique is different from that employed by today’s soccer-style kickers. They approach the ball from the side, the holder tilts the football, and they strike the ball with the instep rather than the toes.

While the two styles of kicking coexisted for the better part of two decades, the soccer-style kickers won out.

MECHANICAL ADVANTAGE

Let’s take a look at the biomechanics of kicking, to see how and why the soccer style has taken over and whether the straight-on style has anything to say for itself.

First off, it’s not surprising that straight-on kickers could match, and sometimes exceed, their soccer-style colleagues.

“In a foot-ball collision, the ball goes off at about 20 percent faster than the foot is traveling,” according to Adrian Lees, a professor of biomechanics at Liverpool John Moores University in the United Kingdom. “However, this percentage can be increased or reduced depending on how rigid or flexible the foot is.”

Straight-on kickers lock their ankles, with the foot approximately perpendicular to the leg, which enables them to transfer the kinetic energy of the swinging leg to the ball very efficiently. Soccer-style kickers hold their foot at a more obtuse angle at the moment of impact, which means some of the leg’s energy is absorbed by the flexing ankle joint. Soccer-style kickers use a couple of tactics to overcome this disadvantage.

If you watch the Redskins’ Graham Gano or the Baltimore Ravens’ Billy Cundiff, you’ll see that their hips swivel during the windup and follow-through of their kick.

“The angled approach allows players to rotate their body segments in more than one axis, not only in one plane, and this seems to make them a bit faster,” says Eleftherios Kellis, a professor of sports science at Aristotle University of Thessaloniki in Greece.

OUCH!

Soccer-style kickers also can decrease the dampening effect of that flexed ankle by striking the ball high up on the foot. Hitting the ball on the instep means more of the leg’s energy is transferred to the ball because the ankle doesn’t bend as much upon impact. (Shoes also absorb some of the force of impact, which is why many kickers used to kick barefoot. Improvements in shoe technology — partially combined with an aversion to pain — have virtually eliminated barefoot kicking.)

But striking the ball with the laces introduces an additional complication: The kicker must contact the ball at its center. For most people, trying to smack the center of the ball with the laces of his kicking shoe risks dragging the toe along the ground. So the kicker has to drop his body down slightly when approaching the ball.

The biggest benefits of the soccer style seem to come in accuracy. The nonkicking leg of a soccer-style kicker is in a better position to control his movements. His bent nonkicking knee absorbs the impact of landing rather than transferring an enormous jolt through the body.

Stability through the moment of impact is crucial to making the ball go where you want it to.

ActiveStyle, Pages 27 on 10/24/2011

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