Analysing the one-leg jump, part I: The Run-up and amortization phase

Watch the above video and you’ll agree with me – the one leg jump is both natural and majestic. To me, the one leg jump is the most natural way to jump. I could never understand the two leg jump. Blame it on anything – me being naturally weak, not having the right structure, having weak quads, not recruiting the right muscles in the two-leg jump, not practicing it enough… blame it on anything, but the one leg jump IS the natural way to jump in my opinion because that’s how we walk – unilaterally. We don’t bounce on two feet when we walk around all day long. Why? Because it’s inefficient to do so.

OK, so maybe it’s inefficient to walk bilaterally but who says it should be inefficient to jump bilaterally? Aren’t they different events, with different demands? Well yeah, they are, but as a good progression that comes naturally, once you learn how to crawl, then you can learn how to walk, then you can learn how to run, then you can learn how to sprint, then you can learn how to JUMP off one leg. Because a jump off one leg is just an exaggerated “skip” where you just choose to modify the angle of the applied power in the ground.

It is also, assuming you move correctly to begin with, actually less stress on your knees because less knee bend is involved and less quad contribution and eccentric bent-down is involved.

So how can that be? I bet a lot of you will say “no way a one-leg jump is LESS stressful on your joints than a two leg jump is – it’s only one leg that has to do the work of stabilizing the entire weight of the body and then propel that weight upwards, so therefore there is MORE stress”.

Well, sometimes that’s right, sometimes that’s wrong. It really depends on your structure and the distribution of strength in your body, but also on your movement efficiency in the two movements. There are a lot of factors at work.

For example, for me – assuming I’m not too heavy – a one-leg jump off my left leg is pretty much effortless. A one-leg jump off my right leg is TERRIBLE. A two leg jump requires quite a bit of effort and my knees feel a ton of pressure at each of these, despite the fact that I’m using two legs to dissipate that amortization tension in my plant.

What’s going on?

The thing with the one-leg jump is that, assuming you have practiced it enough, tends to become very hip dominant. The glutes and the hamstrings will do the most of the concentric power exerted in the jump, with contributions from the quads and the calves to prevent the knee from collapsing and power to be leaked out/the jump to be failed altogether.

During my time jumping off my left leg ever since I was 15 and had a 12 inch one-leg jump off my left leg, EXTREMELY quad dominant – my technique has naturally evolved towards a hip-dominant jump without me doing anything to change it to that. I didn’t even know what that meant at that time. I was just jumping at the rim. It just happened.

I think one of the most important things about the one-leg jump is its explosive-isometric amortization phase which is different than the more eccentrically-oriented two-leg jump amortization phase. In the two-leg jump, after you touch the ground there usually exists an eccentric phase where you continue to go down a bit to generate some range of motion out of which you have enough time/you have the right position to generate some upwards concentric power.

In the one-leg jump, however, you basically plant your leg and you don’t get down – you don’t have an eccentric phase per se – instead you have an explosive-isometric phase in which you just try to stay as stiff as possible and let the entire leg muscle-tendon complex accumulate tension from that plant, tension that is then, when reaching the right position, to be released for the jump itself. The term “explosive-isometric” has been coined by Joel Smith (I’ve heard it first from him) – and is an excellent term to use about what actually happens in the amortization phase of the one leg jump.

You don’t need to lower your center of gravity in the one-leg jump to generate some range of motion out of which to express power because, if you had the right run-up, you already did it using the penultimate step. The penultimate step is the step before your last step (before your actual plant step). What happens in efficient jumpers is that the penultimate step is long, which in turn makes the center of gravity to lower, then the plant step is a bit shorter than the penultimate step and puts the body at the correct angle to perform whatever kind of jump the athlete wants (either as high as possible, as long as possible, or somewhere in between).

So let me use some pictures to demonstrate a few points:

Penultimate step picture
The penultimate step in the one-leg jump

Here you can see the penultimate step in a free-throw line dunk jump. Video is this:

You can see the position of the body is kinda “together”, with the ball close to the body and in front, straight back, the front knee slightly bent, the foot of that leg dorsiflexed (foot of the right leg).

Continuing into the plant phase (in the actual amortization phase):

Amortization phase picture
The amortization phase

You can see the ball has moved towards the left side of the body (loading the jumping leg with that weight), still close to the body, and also the knee is just slightly bent on the left leg and the foot of the jumping leg is dorsiflexed. The trunk is vertical.

Then, as the actual jump occurs:

Takeoff phase picture
The jump takeoff phase

At this point the whole body is being extended, with the trunk being in front of the body as the jump happens, the right knee pendulates upwards to make the weight of the body lighter (basically it’s a vector of force upwards) and the arms, with the ball, begin to extend forward towards the goal (the basket).

The important thing to notice here is that the left knee is kept completely straight, as you want to pivot around the foot generating power with the glutes and the hamstrings and not have a break at the knee in that long lever of the entire leg. THAT IS KEY – YOU DON’T WANT TO BREAK AT THE KNEE OR TO EXCESSIVELY USE THE QUADS

Doing so will generate:

1) A failed jump, where you collapse in the jump

2) A severely sub-optimal jump due to the loss of leverage (a shorter lever that ends at the knee instead of ending at the ground)

3) A ton of knee stress

To illustrate this point I have managed to catch one of my failed jumps on camera. In this jump I’m about to show to you you’re going to see what happens when you plant with a bent knee and try to jump off that leg with a bent knee.

What you see going on in there is my knee collapsing and putting me at terrible risk for knee injury, not to mention the completely failed jump:

Raptor knee collapse picture
This is how knee collapse looks like

So obviously, that’s what you need to avoid and that’s what happens when:

  1. You’re tired
  2. You’re using the wrong shoes
  3. You’re weak
  4. You don’t get to the jumping point in the right position
  5. You use a speed you can’t control
  6. You don’t trust the jumping surface enough/you don’t feel safe on it
  7. You’re a quad dominant guy trying to jump off one leg
  8. You use the inappropiate armswing for that particular plant
  9. You’re too heavy
  10. You have some faulty muscle firing/recruiting issues

THESE are the 10 things I would like to discuss in the 2nd part of this article, where we must address them and see how we can find solutions for every one of these issues. I will err on the side of overanalysing only to end up simplying the process in the conclusion.

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