Jumping

[onix]

I don't know how many countless dreams I've had about flying like MJ and dunking, but have also wondered about the dynamics. When I was younger I could jump higher off two feet than after a running start. Nowadays, I jump just as high regardless of how. By the way, I get about 30" of vertical - nowhere close to MJ who got something like 48", but I think a lot better than most.

So question:

Why would I be able to jump just as high off of one foot as I would when both legs and feet are being used?

 

[Gibsons]

Originally posted by: onix
I don't know how many countless dreams I've had about flying like MJ and dunking, but have also wondered about the dynamics. When I was younger I could jump higher off two feet than after a running start. Nowadays, I jump just as high regardless of how. By the way, I get about 30" of vertical - nowhere close to MJ who got something like 48", but I think a lot better than most.

So question:

Why would I be able to jump just as high off of one foot as I would when both legs and feet are being used?

From a running start you can convert forward momentum into upward. Also, when you jump off one leg, the other leg is still doing work (it kicks up), so it's power isn't wasted.

 

[onix]

Originally posted by: Gibsons

From a running start you can convert forward momentum into upward. Also, when you jump off one leg, the other leg is still doing work (it kicks up), so it's power isn't wasted.

OK so conservation of energy - but you're not jumping off a spring-board and our leg muscles are not elastic. Also at some point, if I run too fast, I cannot jump very high at all.

 

[Gibsons]

Originally posted by: onix

Originally posted by: Gibsons

From a running start you can convert forward momentum into upward. Also, when you jump off one leg, the other leg is still doing work (it kicks up), so it's power isn't wasted.

OK so conservation of energy - but you're not jumping off a spring-board and our leg muscles are not elastic.

Or maybe they are.

 

[dkozloski]

Franklin Jacobs who is 5 feet 8 inches tall cleared the high jump bar at 7 Feet 7 1/2 inches. That's 2 feet over his head. He can do a two handed reverse slam dunk. By that standard MJ should be able to high jump 8 feet 6 1/2 inches.

 

[Mday]

if you are running, your foward momentum is not converted to any upward momentum. when you jump while running, you're still going foward. If you jump during a normal running start, you lift yourself with one leg which would effectively decrease your leap height. If you stop and jump with both legs, you will for most purposes STOP for brief instant and then leap, in which case the power used by your legs is used to STOP for that brief instant which decreases the power used to do the leaping, which decreases the potential height reached.

 

[dkozloski]

Get yourself a coaches film of Dwight Stone's technique. A circling run-up with the final step a deep dip and a straightening of the leg at the khee so that the effect is like a pole vaulter propelling himself over the bar with the lift of the pole. His forward motion is converted to upward by the translation of the arc of the pole or in this case the leg. The pole vaulter captures the end of the pole in the box but a high jumper depends on the traction between his shoe and the run-up area. That's why a high jumpers career often ends with a blown out knee. A broad jumper uses the same technique with a much faster run-up because he wants to convert height and velocity to distance.

 

[Sushifiend3000]

Originally posted by: Mday
if you are running, your foward momentum is not converted to any upward momentum. when you jump while running, you're still going foward. If you jump during a normal running start, you lift yourself with one leg which would effectively decrease your leap height.

In the long jump and high jump, the training emphasis is on speed and technique, not "jumping" per se. Since vertically launching yourself into the air requires the most physical effort (working against gravity and all), jumpers are trained to use that forward momentum to their advantage and apply the plant leg in much the same way that a pole vaulter uses the pole. Converting forward momentum to upward is key in both disciplines, to conserve energy and to allow you to concentrate on coordinating your limbs. All track and field jumpers get plenty of sprint drills in training.

If you stop and jump with both legs, you will for most purposes STOP for brief instant and then leap, in which case the power used by your legs is used to STOP for that brief instant which decreases the power used to do the leaping, which decreases the potential height reached.

In a running two-footed dunk in basketball for example, rarely do both feet land at the same time before the leap. You'll see that the weak foot lands first, and the strong foot lands in front of it with the body at an angle to the basket. The forward momentum is stored in the penultimate step as the legs bend and the body dips. Momentum is transferred from the back foot, mainly used for balance, to the plant foot which launches the athlete into the air. There is no stopping; it's executed in one fluid motion. Coordination and strength are the keys to conserving as much of that energy as possible.

Source: Four years in track (long/high/triple jumps and hurdles) and basketball, two bad knees.

 

[onix]

Originally posted by: Sushifiend3000

In a running two-footed dunk in basketball for example, rarely do both feet land at the same time before the leap. You'll see that the weak foot lands first, and the strong foot lands in front of it with the body at an angle to the basket. The forward momentum is stored in the penultimate step as the legs bend and the body dips. Momentum is transferred from the back foot, mainly used for balance, to the plant foot which launches the athlete into the air. There is no stopping; it's executed in one fluid motion. Coordination and strength are the keys to conserving as much of that energy as possible.

Source: Four years in track (long/high/triple jumps and hurdles) and basketball, two bad knees.

About how much additional vertical should one expect with a running start, instead of off two?

 

[Sushifiend3000]

About how much additional vertical should one expect with a running start, instead of off two?

I don't have the expertise in biomechanics to quantify that, but I wouldn't assume that a running jump will get you more height than a standing one.

Why would I be able to jump just as high off of one foot as I would when both legs and feet are being used?

Are you sure that that is the case? If you're talking about getting closer to the rim, jumping off of one foot gives you a reach advantage, so that's not really a fair way to measure it. Vertical jump is measured by "hang time" - the athlete takes one step and jumps straight up from a pressure-sensitive pad with knees locked until touchdown. You would have to do the same with a running jump to make a comparison.