Studying the mechanics of throwing

Fort Worth, TX

9/14/2009

When it comes to throwing a ball better, the secret simply may be to listen to your body. That’s one finding from research by Dan Southard, professor of kinesiology at TCU. 

Given the right circumstances the motor system is “self-organizing,” explains Dr. Southard. “It will take advantage of the laws of physics.”

Efficient throwers take advantage of something called the open kinetic chain to allow for the transfer of velocity from proximal (e.g. body trunk) to distal (e.g. hand) segments. An open kinetic chain is a system of links where each link in the chain may be affected by movement of other links – such as the human arm.

A baseball pitcher, for example, rotates the trunk of his body which has a relatively large mass. When trunk rotation slows down, the angular momentum that was created is transferred to the less massive upper arm.

The result of this transfer is a dramatic increase in angular velocity of the upper arm in order to compensate for the less massive distal segment. This increase in velocity continues down the kinetic chain to the forearm and finally the hand.

Each distal segment increases in velocity as its proximal neighbor slows down because each distal segment is less massive than its proximal neighbor. This increase in velocity will not occur unless the distal segment is less massive and lags behind its proximal neighbor.

“When each distal segment lags behind its neighbor the result is “efficient distal lag and a higher velocity throw,” notes Dr. Southard. “The pitcher’s body acts like a whip with energy transferred to body segments that have progressively less mass resulting in an increase of the segment’s velocity.”

Poor throwers do not exhibit distal lag and velocity goes way down. Fortunately for throwing, our bodies are naturally tapered proximal to distal and this tapering along with distal lag allows us to take advantage of the transfer of angular momentum and throw faster.

“The cartoon character Popeye, for example, would have a disadvantage when it comes to throwing because his forearms are more massive than his upper arms,” notes Dr. Southard.

In several experiments with children and adults Dr. Southard has noted that “one of the circumstances to get people to take advantage of the open kinetic chain and develop distal lag is to ask them to throw faster.” Attempting to throw faster promotes distal lag and allows the thrower to take advantage of the transfer of velocity.

“We have asked poor throwers to simply throw faster. When they reach a certain percentage of their maximum velocity they demonstrate distal lag and throwing patterns become more effective. “First, we see the hand lag behind the forearm, then with the forearm lags behind the upper arm, and finally the upper arm lags behind the trunk.”

In his latest research Southard found that it isn’t just the lag that is important to throwing effectively but it is also the amount of lag that identifies better throwers. Southard and his research team found that better throwers had less lag time between the hand and forearm but more lag time between the forearm and upper arm than poorer throwers. He has suggested that the degree of distal lag by segment may be important to identifying good throwers.

The research was published in the June 2009 issue of the journal Research Quarterly for Exercise and Sport.