Next time you watch a basketball or volleyball game, notice how
high the athletes jump to block a shot or spike the ball. Ever wonder if
you could jump as high?
Stand next to a wall with a short pencil in your hand and hold your arm
as high above your head as you can, keeping your feet flat on the floor.
Make a mark on the wall to note your standing reach. Then jump as high as
you can, keeping your arm high above your head. At the top of your jump,
make another mark on the wall. It works best to stand close to, but not
touching, the wall when you jump. The difference in height between the two
marks is a measure of how high you jumped.
You may be able to jump higher if you change how much you bend your knees
before jumping. As you straighten your knees, you push your feet harder
into the floor, which allows you to push off the ground with more force
and jump higher. If you don't bend your knees much, you don't get much extra
push. On the other hand, a deep crouch overstretches the thigh muscles,
making them less efficient in pushing you off the ground. Experiment to
find the amount of knee bend that gives you the most height.
Swinging your arms up can also add to your jump's height. As your arms
swing up, your body is forced downward in reaction, increasing the force
with which you push off the ground, and, therefore, the height of your jump.
To be effective, your arms must finish their upward motion before your feet
leave the ground.
This method of measuring a person's vertical jump is known as a Sargent
jump, after Dudley Sargent, one of the pioneers in American physical education.
When he studied a group of college students early in this century, he found
that, on average, they jumped about 20 inches. There are no official records
for a jump like this, but in 1976, basketball player Darrell Griffith's
standing vertical jump measured four feet!