[Agility Lab] False-Step/Plyo-Step: Right or Wrong?

Every 6-months or so this comes up in conversation on Twitter. There is always a little debate but generally most people are on the same lines. That is, if you need to move somewhere, it doesn’t matter if it is forwards backwards or side to side, you need to have the relevant shin angle to the ground and be able to apply force in the correct direction. This means that if you start with a bilateral standing stance, you need to adjust the BOS and COM relationship to move forwards. There isn’t any debate on that component, but there is when comes to discussing how to do it.

Most discussions and contexts are around a linear sprint start when there is a bilateral stance and a stimulus to react to. I have written about this topic more extensively in the past, so I won’t completely go over old ground. Read my other article here. But here is a clearer understanding of the fastest process which I’ll expand on from the literature.

To adjust our BOS and COM relationship and apply force, you first need to lower your COM.

The speed at which you lower your COM will be increased if you are weightless, meaning your feet aren’t in contact with the ground.

But to be weightless, BOTH of your feet need to ‘leave’ the ground (I have some hesitations with the literature here). And if the purpose of this is to lower the COM in order to apply force in a different direction, it is logical to assume that when the feet are returned to the ground, they are placed in the most advantageous position possible, as soon as possible.

The main leg that gets considered is the one which travels behind the COM the farthest (this is the false-step). This leg is the easiest to optimise shin angle in as it is BOS manipulation dominant, whereas the front leg is COM adjustment dominant. This rear leg hits the ground first, in order to begin to adjust the COM, facilitating the front leg force application. Hence my description of ‘Lift – Pop – Push’.

Generally, the research supports this but there are a few discussion points. One of my research frustrations (especially in biomechanics) is you don’t always know exactly what they did. Given we don’t print journals anymore, surely there should be a move towards data collection videos with publications?

Generally, papers look at a fale-step vs a split stance vs a parallel forwards step. One paper has also looked at a split stance false-step (start in a split but swap feet to accelerate) which I’ll touch on.

As explained above, I am of the opinion that the most effective ‘false-step’ movement should be bilateral. Lift both feet, place the rear one down first then the front one down second. The front foot lands in a more advantageous position than it started. But I am not sure if this is what happens in a lot of the research data collection. Here is a quote from Frost et al., 2008

“On the audio command, the first movement was a step backward with the right foot. Subjects were permitted to raise their left foot as the right went back, permitting that the first step forward was also with the right foot”

If you are going to raise the left foot in this example (it might not riase), I don’t think we should constrain where an athlete puts it back down, and in my opinion, it should be in-front of the start line. Here it is described that it isn’t in-front. If you are going to lift it to speed the lowering of the COM, why put it down in the same place?

This may be semantics, as this paper does report that the false-step is faster than a forwards step if performance is measured by time to 2.5 and 5m in a sprint. But interestingly, there was no difference in the time to the first gate between a forwards step and a fase-step (the participants reacted to a buzzer, which started the timing and the first gate is 50cm away). But unsurprisingly the split stance (like a sprinter) was fastest all the time (it always will be).

The key thing this highlights is that the propulsive benefit of the false-step needs to supass the time it may take to lift the feet and replace before applying force. I would normally say that it will, but in this instance, the advantage from the false-step was somewhat negated by the time it takes to do it. But remember that even though they didn’t get to the first gate faster, they did have a higher velocity which impacted the performance later. I would question though, if the participants were allowed to false-step and also adjust the front foot more effectively, would that have made the difference? In my opinion yes, it’s a few cm, but this is just a 50cm window.

Other papers also support the general conclusion that a false-step is superior (faster over 5m and increased force and power parameters) and that most athletes adopt this movement naturally.

“All subjects in our experiments had such a reaction and had difficulty to perform the test in an-other way”

All of the examples so far are linear acceleration. The laws of physics don’t change when we more to a different plane, but seeing the false-step movement is a little less common in the frontal plane. This is because in the frontal plane, a bilateral stance already puts the BOS outside the COM. As te COM is in the cenbter of the pelvis and the feet are either side of it. But in the sagittal plane, the feet are directly beneath it. Hence the increased need for sagittal plane adjustment. The wider the feet start in the frontal plane, the less need for adjustment as the shin angle (at least on the outside leg) is already present. In fact Goodwin and Collyer (2012) reported that in the frontal plane, only 7 of the 13 subjects naturally false-stepped but all but one did in the sagittal plane.

The only paper which throws a spanner in the works is LeDune et al., 2012 who reported the false-step to be slower than the parallel forward step start when measuring displacement over the first three steps of a sprint. But, the timing didn’t begin until the athlete was in motion, which removed part of the benefit and it also isn’t described as a reactive task. This might just be a methodology omission. But if it wasn’t reactive and it was a self selected start time, I am again less surprised in the forward-step benefit. When you let athlete start in their own time, they will have subtle changes in moving COM forwards, weight onto the fore foot and some pre-activation to help the forward step all of which could have happened here. Combined this with the timing start point and the false-start benefits could well be negated. Video’s please!

What is really interesting and also I think supports my point about a bilateral foot adjustment is that Johnson et al., 2010 reported a staggered false-step was faster than regular false-step. A staggered false-step being when the athlete starts in a split stance, but then switches both feet (bilateral adjustment) before accelerating.

 

One again I want to see everything on video before making any crazy conclusions, but my recommendation is that a false-step with both feet adjusting is superior in any reactive start scenario as long as there is a need to adjust the BOS to improve force application.

My final point is on individual differences, while the Jon Goodwin paper discusses participant preferences and it is pretty consistent, in practice I do once in a while see some outliers. These are usually athletes who are relatively concentric dominant and lack reactive qualities. Therefore their preferred strategy is to forward-step and not lift and replace (false-step) as it reduces available contact time (time to produce force) and increases their need for early RFD and pre-activation. Another example of where the time that it takes to lift and replace needs to be short enough that any propulsive improvements off set that. If you are slow at lift and replace and also really un-reactive it might just tip the scales.

Shoudl we change this? In my opinion over time yes. But it should be driven by changes in the underlying qualities and not just an acute coaching intervention. If we ask them to do something which they dont have the physical attributed for, there is a good change they get worse not better.