AMT Jumps

Training Powerlifting
21

To keep with the calculus comments, I’ll throw something out there that could be an added reason for AMT jumps. If acceleration is constant (as with the higher box jumps), than the rate of change of acceleration (3rd deriv) = 0. With bands the acceleration is not constant, so the rate of acceleration is different.

Since maximal force (F=ma) is different than maximal power output, perhaps having a different rate of change of acceleration might have an effect on power absorption and thus power production?

Food for thought, I have nothing to back any of that up.

22

OK, let’s get off the physics for a second. We agree that you can acheieve the same velocity with bands as with greater height. I believe DB said that it isn’t the greater velocity at impact that he’s after, but the additional acceleration. He argues that when your body feels that you’re accelerating at greater than 9.8m/s^2 it potentiates the nervous system, allowing you to jump higher upon impact. This is what produces the greater(relative to regular plyometrics) training effect.

 This would be difficult to test, which makes me wonder about DB's explaination of AMT's effectiveness.   To test it we need to do what we've been arguing over:  have someone use a box without bands and a lower box with bands, each at the appropriate height to acheieve the same velocity upon impact.  Then you measure jump height for each.  Unfortunately, you would need a way to measure velocity or calculate the average force of the band over the time you fell. The first would be expensive and the second difficult to accurately calculate.

 Anyway, sorry about the long winded comments.  Just food for thought.
23

[quote]Yoda-x wrote:
OK, let’s get off the physics for a second. We agree that you can acheieve the same velocity with bands as with greater height. I believe DB said that it isn’t the greater velocity at impact that he’s after, but the additional acceleration. [/quote]

That makes more logical sense, since the impact forces are the same if the terminal velocity is equal…

I think it can be easily done, at least to the point of qualification anyway.

It may be difficult to get the exact numbers but its easy to see if one is greater or lesser than the other to some extent; same goes for the training effects.

24

[quote]jtrinsey wrote:
To keep with the calculus comments, I’ll throw something out there that could be an added reason for AMT jumps. If acceleration is constant (as with the higher box jumps), than the rate of change of acceleration (3rd deriv) = 0. With bands the acceleration is not constant, so the rate of acceleration is different.[/quote]

So, during the AMT jump, acceleration is greater than gravity.

P= F*V(at impact)

P= ma*V
Whether you use additional acceleration or you use additional height, power at impact is equivalent. If the bands are released at impact then a=gravity at impact and the only other variable is velocity. If velocities are the same then power should be as well.

Thats possible as far as the CNS is concerned but externally there would be no difference in power at impact.

I think its a good observation about the possible effects of +g’s on power output and training effects but it needs to be pinned down further.

Bruce Lee’s 1" punch is very powerful. He is able to generate tremendous acceleration for his fist which results in a high terminal velocity. He also is able to continue delivering power because the mass of his fist is too small for him to generate max power but upon impact he is accelerating a greater load with smaller joint angles and is able to administer additional power.

In a depth jump, your bodyweight is your load and joint angle is equivalent between AMT and regular drop. Typically, max power is thought to be generated between roughly 50-70% of a 1RM load for a given movement. Meaning that F and V are maximized in this load range. An athlete may be able to generate more power if extra load is utilized, ie: weighted vest(mass), bands are used(acceleration), or a taller drop height (velocity) since P=FV=(MA)V

As I understand it though, in depth jumps its more a matter of muscle stiffness allowing elastic tendencies of tendons and connective tissue to translate downward force into upward force rather than muscle actions ability to accelerate or decellerate a load.

Just some thoughts…

25

Technically, Power is equal to the integral of Fdv. If force is constant, then P=Fv. However, if the force is not constant, then the answer will be different. Since impact is not instantaneous but rather best modeled by a delta function (I think…) where t does approach 0, the fact that a is not constant could affect the equation and thus power absorption and production.

Additionally, since an athlete does not “bounce” of the ground, but rather absorbs the impact and will spend as much as a full second on the ground, the bands might continue to provide some downward force while the athlete is on the ground.

Again, I’m just throwing out some half-assed theory. I really don’t have any practical experience to draw from.

I think the best experiment to verify this would be to measure time spent on the ground by an athlete. Since Power is the change in energy with respect to time (rate of change of energy), the amount of kinetic energy at impact should be the same. That is, put an athlete on a box with bands and then on a higher box without bands so that the intial potential energies are the same. If the athlete spends less time on the ground with the AMT setup, delta t will be less and therefore power will be greater. Producing a greater power absorption stimulus with the same intitial kinetic energy is the whole point of doing rate work, correct?

Any thoughts on that?

[quote]Donzi wrote:
jtrinsey wrote:
To keep with the calculus comments, I’ll throw something out there that could be an added reason for AMT jumps. If acceleration is constant (as with the higher box jumps), than the rate of change of acceleration (3rd deriv) = 0. With bands the acceleration is not constant, so the rate of acceleration is different.

So, during the AMT jump, acceleration is greater than gravity.

Since maximal force (F=ma) is different than maximal power output,

P= F*V(at impact)

P= ma*V
Whether you use additional acceleration or you use additional height, power at impact is equivalent. If the bands are released at impact then a=gravity at impact and the only other variable is velocity. If velocities are the same then power should be as well.

perhaps having a different rate of change of acceleration might have an effect on power absorption and thus power production?

Thats possible as far as the CNS is concerned but externally there would be no difference in power at impact.

I think its a good observation about the possible effects of +g’s on power output and training effects but it needs to be pinned down further.

Bruce Lee’s 1" punch is very powerful. He is able to generate tremendous acceleration for his fist which results in a high terminal velocity. He also is able to continue delivering power because the mass of his fist is too small for him to generate max power but upon impact he is accelerating a greater load with smaller joint angles and is able to administer additional power.

In a depth jump, your bodyweight is your load and joint angle is equivalent between AMT and regular drop. Typically, max power is thought to be generated between roughly 50-70% of a 1RM load for a given movement. Meaning that F and V are maximized in this load range. An athlete may be able to generate more power if extra load is utilized, ie: weighted vest(mass), bands are used(acceleration), or a taller drop height (velocity) since P=FV=(MA)V

As I understand it though, in depth jumps its more a matter of muscle stiffness allowing elastic tendencies of tendons and connective tissue to translate downward force into upward force rather than muscle actions ability to accelerate or decellerate a load.

Just some thoughts…
[/quote]

26

[quote]Chris Arp wrote:
climbon

This means that you could jump off a 10 story building and that would not change the forces at landing???[/quote]

Again I never claimed to be a physics expert or that my explanation was correct. It was just something that seemed to make sense in my head. I knew it was not as “simple” as I was stating. I appreciate the other posts showing my error (that is why I was also asking for correction) and aplogize for my previous explanation.

27

[quote]Yoda-x wrote:
climbon wrote:

No because that breaks the laws of physics. The speed at which you are falling is the speed of gravity. Changing the height of the box does not change the speed of gravity. The bands increase velocity or acceleration and would be needed at each box height to achieve the desired effect.

F=ma: Mass is our bodyweight; Acceleration is gravity.

You can increase force by adding weight which will increase the mass, but acceleration will remain at the speed of gravity.

You can increase acceleration by adding bands. Then a=gravity + pull of bands. This also increases force.

Both options are valid, but the effect is a little different since either mass or acceleration are changed. That is why I posted earlier that you would not get the same result trying to perform AMT jumps holding dumbbells. The dumbbells would increase force but the result would not be similar to AMT jumps that are increasing acceleration.

Again, I am not an expert in physics and I may not be entirely correct in my explanation. If not, I apologize and ask for someone to correct me.

Gravity provides acceleration, which is the rate of change of velocity (speed) over time. When an object falls from a low height it hits the ground at a lot velocity, although it has constant acceleration (9.8m/s^2, the acceleration due to gravity). Things do not fall at the “speed” of gravity, they all fall with constant acceleration due to gravity, which means they all pick up speed at the same rate. An object falling for 1 meter will strike the ground at 2.2 m/s and will accelerate at 9.8 meters per second squared. I’m saying that striking the ground at 2.2m/s, for example, is the same whether or not you use an elastic band to accelerate or greater height.[/quote]

Sorry. I mistakenly said speed of gravity. Thank you for the correction.

28

[quote]jtrinsey wrote:
Technically, Power is equal to the integral of Fdv. If force is constant, then P=Fv. However, if the force is not constant, then the answer will be different. Since impact is not instantaneous but rather best modeled by a delta function (I think…) where t does approach 0, the fact that a is not constant could affect the equation and thus power absorption and production.[/quote]

Why make it so complicated? Force is constant. Gravity is the primary force and the bands add some extra that can be average througout the entire drop time. If you are talking about the post-impact forces/velocities and acceleration components thats easy to measure: Vertical Jump. Now you have a way to compare the power absorbtion and resultant production using the two jump methods as long as terminal velocities are equivalent.

We are not trying to find the absolute value of power in either situation. (AMT or elevated box jump)

I’m just trying to figure out why AMT jumps are different from a box jump from a taller box.

Thats a good point and one that I think will make a difference between the two methods if there is one.

[quote]
I think the best experiment to verify this would be to measure time spent on the ground by an athlete. Since Power is the change in energy with respect to time (rate of change of energy), the amount of kinetic energy at impact should be the same. That is, put an athlete on a box with bands and then on a higher box without bands so that the intial potential energies are the same. If the athlete spends less time on the ground with the AMT setup, delta t will be less and therefore power will be greater. Producing a greater power absorption stimulus with the same intitial kinetic energy is the whole point of doing rate work, correct?[/quote]

Yeah, sounds good; except for the use of time of contact. The bands may increase KE after impact and that would negate use of time as the only variable.

VJ after impact is a really good measure of resultant power. It pretty easy to measure too.

29

Haha, I know I’m making it way more complicated than it needs to be. This is what happens when math majors get interested in strength training!

You bring up a good point about KE after impact. One other reason not to measure ground time that I just thought of: it would be difficult to tell how much time is spent absorbing the impact and how much time is spent producing power for the jump. That kind of ties in with what you were saying. I agree that a VJ test would be a good way to do it.

Now I would like to see somebody with access to a multiple athletes and the equipment needed to perform this test chime in. Or maybe somebody that can give any other reasons as to why AMT jumps would be superior to higher box jumps.

I also have another question. I’ve seen some trainers perform kind of a “reverse AMT jump” (for lack of better terminology). Basically bands around a belt tied to the floor with the athlete starting on the floor. Athlete jumps up, bands pull down and the athlete absorbs the impact on landing. Advantages/disadvantages to this? I would say it would be inferior to AMT/depth jumps because you don’t get the stretch reflex on landing to produce additional power on your jump, you are kind of doing it backwards when starting with the jump first. However, would this type of jump training still have use as an alternative stimulus?

30

I relate that to weighted implement training. It may have some uses, but you have to make sure that the amount of resistance added does not alter technique.

31

Climbon,

Do you feel that jumping with any sort of resistance will alter mechanics? Specifically in terms of weighted vests or bands.

If so, could the jumping motion be made “non-specific” enough to not interfere with motor patterns? For this I’m specifically thinking about some sort of 1-legged squat jump.

32

[quote]jtrinsey wrote:
Climbon,

Do you feel that jumping with any sort of resistance will alter mechanics? Specifically in terms of weighted vests or bands.

If so, could the jumping motion be made “non-specific” enough to not interfere with motor patterns? For this I’m specifically thinking about some sort of 1-legged squat jump.[/quote]

don’t add more than 10-15% of your bdoyweight and your fine.

lunge jumps work well for running one legged jumps I’ve noticed

33

[quote]climbon wrote:
To go along with what Jumanji said, holding dumbbells will not increase your drop speed since gravity is constant (as long as you take out friction, etc.). A simple physics demonstration is to use a piece of paper or feather and a heavy textbook. Place the feather or paper on top of the textbook and drop them. They will fall at the same rate. If you do it separtely, they will not fall at the same speed, but this is secondary to other things like friction, drag, etc. (A physicist could explain this much better than me.) Given our weight, these secondary factors are not going to come into play and dumbbells will not speed up gravity.

The bands will speed up our decent because of their elastic component. They do not speed up gravity, but they will “propel” us toward the ground.

You also would not start with AMT jumps. You need to have considerable amounts of strength and force absorption before attempting them. They are high level and require some time to build up to. [/quote]

I am no physicist… But I did stay at a Holiday Inn last night.

The rate of acceleration on any object is -9.81m/s.

The only thing that affects how fast it hits the ground is the surface area. Two dumbbells (if anything)would not decrease time from the time you jumped, but increase it (clearly by an insignificant number, anyway.)

My teacher proved this to us by putting a marble and a feather in a fish tank (or something like it) that wsa completely air tight, where he would pump all the air out of it. Once all of the air was out, he released the marble and feather at the same time (via mechanism, in the tank) and they both hit the bottom of the tank at the same time.

34

CoolColJ,
I’ve heard the 10-15% recommendation on loaded sport movements before so I’m with you on that. However, I was more discussing “non-specific” movements. I chose 1-legged squat jumps because that I would think that loading that movement wouldn’t really interfere with motor patterns.

rrjc,
Adding bands would increase the acceleration due to additional kinetic energy. Whether the additional acceleration actually matters is a subject of debate I suppose.

35

Have the people here saying that AMT jumps are the same as a depth jump from a higher box ever tried squatting with bands? It’s defintely a different feel than squatting with more weight, you feel like you’re accelerating more. The bands act as more acceleration, but you land while under that speed for less time so there’s less force at impact. You teach your body to turn on under a higher acceleration without the excess force… or at least that’s my understanding of it.

36

jgvbl,

I think there is a little bit of a difference here. Squatting with bands is set up so that the band resistance is high at the top of the squat, with AMT jumps this is not possible, the maximum resistance will be applied when you are already in the air.

However, I would imagine there still would be some additional force added by the bands throughout the landing/jumping part where the feet are on the ground. I think the debate is whether or not that matters and if it does, if it superior to simply jumping off a higher box.

37

I’m saying that the bands add a sort of ‘hypergravity’ to the exercise. Gravity accelerates you to the ground at a constant rate here on earth… 9.8 (?) m/s/s. Now if you were to up that acceleration through bands, you’ld be teaching you’re body to ‘turn on’ under a faster acceleration, which is the point. Yes the force and speed would be about equal from jumping from a higher box, but the acceleration is different.

And the squatting example was to just show that yes the force might be the same at the top of a squat with the same amount of band tension versus the amount of weight, but it ‘feels’ different because there’s different types of forces working on your body… or at least thats how I understand it, I might be wrong…

38

jgvbl,

I see what you are saying now, I misunderstood a little at first. I agree that the “hypergravity” thing might be a factor (see my earlier post when I got nerdy and started talking about 3rd derivatives and such) as to why AMT jumps would be superior.

I think this might be why squatting dynamically using bands, you are teaching your muscles to be able to store more energy during the power absorbtion phase.

I think we can all agree that the key to producing power is being able to absorb it. Certainly AMT jumps are a more advanced technique that can help us do this. Whether they are clearly better than higher box jobs might still be a matter of debate until proven (although my guess would be that they are), would anybody argue that they are worse?