Moving from left to right in the above images is like sliding along a continuum. Lets say that all of these athletes have the same task, which is to accelerate forward as fast as possible in reaction to an external stimulus.

The sprinter on the left: He’s sorted, he’s already got the shin angle needed and can direct force perfectly, the blocks help that but the principle is the same, even if the position is a little extreme.

The runner in the centre: He’s kind of set up, but if he was racing over a short I’d almost guarantee he will use (and should) a bilateral adjustment of his feet. If it was the start of a longer distance race, he might leave his feet there and just room forwards with gravity, but that is simply because it will be more economically and the intent changes (the time lost isn’t an impact on performance because the duration of the event is so long). But in a short distance competitive task, you’d likely see front foot and back foot lift to optimise force direction (along with some other benefits).

The NFL athlete on the right: Clearly, the position he is in is not useful to sprint linearly forwards as fast as possible. If this was his task, once again you’d see a bilateral BOS adjustment to create the needed shin angles and force direction. Guaranteed.

Sometimes there is a debate about how this shin angle gets achieved. Regardless of the process, the primary lynchpin in a lowering of the athletes COM, or for their COM to simply move further in-front of their BOS. To do this, the athlete has two options:

1)    Keep feet planted where they are (COM is supported), try and push backwards a little but wait for gravity to pull you forwards to get the right COM:BOS relationship. Essentially making COM lowering slower (COM remains supported) and hoping gravity and a little force allows for COM to move forwards. The force can be optimally applied to accelerate.

2)    To lift both feet very slightly, which will allow the COM to drop and allow the BOS location to be adjusted concurrently. Both of which happen faster because the COM isn’t remaining supported and we can both move out limbs faster than gravity can pull us to the ground as lower our COM faster when we aren’t still partially supporting it.

Option 1 is categorically slower than option 2. You see it in practice and the research supports it (although the research is dodgy!). If in practice the athlete doesn’t adjust in this way, it is either because:

1)    They were already in an optimal position

2)   There wasn’t very much intent to move fast

3)   They are just a heavy-footed low RFD athlete who probably isn’t going to be winning the race/be successful

The main time option 2 is an issue is if it is overdone and the COM actually moves backwards, that obviously isn't ideal, But we should be seeing the COM move down and forwards here.

The Details:

When people talk about a false step there is some mix between if this is the front leg, the back leg or both. Or if the front and back leg get named something different.

But notice in my descriptions the detail of recommending a BILATERAL foot position adjustment. Most commonly you’ll see both feet adjust, one maybe more than the other, but there is a period where both feet ‘lift’.

1)     Both feet lift = the COM lowers

2)    The rear leg hits the ground first = to begin to move the COM forwards, facilitating the front leg force application.

3)    The front leg makes contact with now a lower COM and more behind COM location (better force application) = optimised initial propulsion

I call this “Lift – Pop – Push”

Luke Storey recently shared the above video on twitter which generated some good discussion. Lets take a look a each athlete.

Firstly, the task is competitive, loaded (needs extra impulse), short distance and they are all starting in a split stance where there is varying levels of effectiveness. But one consideration here is that when an athlete is in a 2-point stance (no hand toughing the ground) they need to support their mass to stop them falling forward while waiting for the signal to accelerate. To do this the front leg will always be more of an upright shin angle than the back, even further supporting that the BOS needs to move.

Athlete 1: Blue – Good starting shin angle on back leg, a little upright on the front leg. But guess what, a bilateral adjustment. Lift – Pop – Push.

Athlete 2: Black vest – Much taller with a higher COM, shin angles (BOS:COM relationship) far from ideal to accelerate. Therefore we see a much greater adjustment of the back leg. But still a bilateral Lift – Pop- Push

Athlete 3: Black T-shirt – Only a front leg lift here. So why? For me stance starts much more narrow with the weight more over his back foot than his front (front shin vertical with a narrow stance and back leg loaded). So here he doesn’t need adjust his back leg as its already loaded and in a good application position. But this means that his COM is further behind the start line and that his front leg then needed to adjust further to make sure that there can be an effective propulsion step. Making the front leg drive much further behind the start than the others. I don’t think this does him many favours as the load pulls his trunk more upright and his COM lags behind a little (contributing to the front leg step back and also seen in his arm movement). So this one is an interesting example to look at but isn’t exactly what I’d call optimal. Maybe the chain load was a little high for him, who knows.

Some Thought Experiments:

• If the athletes were allowed to place one hand on the ground on the start line, would be have seen the same thing?
• If the athletes know where they needed to go, why didn’t they set up more optimally where they didn’t need to adjustment?

The answer could link to the contribution of the SSC, could also be that it is just difficult to do that without a hand on ground support.

The Research:

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 (no video and poor pictures).

Given we don’t print journals anymore, surely there should be a move towards data collection videos with publications?

Generally, papers look at a false-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 [wut??]) 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. 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 raise), 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 (as its contacting after the rear foot has pushed the COM forwards already). Here it is described that it isn’t in-front. Bit sketchy for me.

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 (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 surpass 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 (maybe because of the front foot constraint and the ‘alien’ instructions the athletes were given). 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 the COM is in the centre 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-stet 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.  

Once again I want to see everything on video before making any crazy conclusions. The task, the instructions and the timing all matter. 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.

Should 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 don’t have the physical attributes for, there is a good chance they get worse not better.

Either way, hopefully we can use some sound biomechanical principles moving forwards and have some clarity!