On September 24, 2023, Tigst Assefa flew through the Brandenburg Gate towards the finish line of the Berlin marathon, startlingly fast even at a glance; stunningly fast according to the clock.
I can’t speak to all the factors involved in her performance. However I can speak to her running form and what it suggests.
Assefa’s form in Berlin in 2023 was strikingly different from the previous year, and the differences grow when we compare the videos. In the absence of any indication she’s done form work or some kind of highly effective physiotherapy, and knowing she wore different shoes this year, I think we can assume her differences in form are an effect of the shoes.
Here’s a video summary of the differences I see. Read on below for a discussion of each.
Assefa’s form change this year is similar to Brigid Kosgei’s form change in 2019, when she raced in supershoes for the first time and set the previous world record. I’d captured slow motion video of Kosgei in the 2018 London marathon in racing flats, and when I filmed her in Chicago I at first didn’t even realize she was the same person, her form was so different. She was more extended overall, with her pelvis tilted forward and shifted forward, and her back subtly arched, with chest slightly lifted. Her arm action was unchanged, but everything else was fundamentally different.
The same is true of Assefa this year compared to last, except she was in supershoes last year as well. Just not the brand-new super-light rocker-sole model she wore a few days ago. These screenshots show the difference:
While Kosgei had been actually a little too flexed before she strapped on supershoes, that wasn’t true of Assefa. She had a great balance between her flexors and extensors last year, so she had a nice, clean lean. This year that has disappeared, and now she’s a little arched, with her head back.
In my experience, this change to a slightly extended form can be produced by a rocker sole that causes the runner to take off from farther forwards on their toes than they otherwise might. This also results in the hip joint being farther past the foot than it otherwise would be requiring more hip hyperextension and usually also more anterior pelvic tilt. If it requires too much, the runner will arch their back rather than leaning more deeply to avoid any danger of faceplanting. Both Kosgei and Assefa did this in new footwear.
One might be tempted to argue that this slightly arched posture must be good for fast running, given the race results. But it actually restricts the airway by taking the runner out of atlanto-occipital extension, and that most definitely is not good. It appears to also reduce the amount of force a runner can put into the ground in late stance to push off.
In actuality, this form change simply indicates that something about the rocker in this year’s shoes is different and having a bigger effect. I don’t know the details, except that the manufacturer trumpeted its innovativeness in a way that suggested it was longer than earlier versions. Longer would make sense for this form change.
Another reported element of the new shoes that plays a role here is the significantly lighter weight. Heavy shoes tend to promote a forward lean, as the runner works to pull the feet forward. To understand this phenomenon, imagine you’re trying to run in quicksand. As you try to lift your foot from the ground and feel it resist, you lean away from the foot to use your weight to try to pick it up. The same pattern applies to the weight of shoes.
There are a lot of good reasons to lean forwards when you run, with the reduction of drag (or air resistance) key among them. So I’m not saying Assefa was leaning forwards last year to deal with inordinately heavy shoes. But since this year’s shoes were so very light—lighter even than old-school racing flats—they provided less need to lean forward even as the rocker triggered arching. To me, this suggests the change in weight was significant enough for her to alter her movement.
Last year Assefa’s head and upper body action was very active–almost pumping. There was obvious tension in her neck (her sternocleidomastoid muscles standing out sharply) and, when seen from the front, a kind of noisy side-to-side action that was difficult to specifically trace but seemed connected to her obvious right/left asymmetry.
Comparing that footage with this year, it suddenly also seems clear how much impact carried through her body to her head. I don’t consider that a bad thing, though again, the noisy action (meaning many conflicting muscle actions occurring together) and tension in her upper body suggested a lot of extra effort.
That seems clear in comparison because you just don’t see the impact this year. There’s still some tension, a bit of a forward/backward bob… it’s not Kipchoge’s smooth bounce. But there’s a shock in each footstep in 2022 that’s gone in 2023.
That could actually be bad for performance, because if you don’t compress the spring, it can’t spring back. Impact drives running when properly channeled. But whatever impact was missing this year was likely made up for by the longer rocker providing propulsion.
Looking at the side-by-side video above, it’s clear that Assefa’s cadence or stride rate was higher in 2023 than in 2022. That defies the typical phenomenon of a slower stride rate due in supershoes due to the large amount of foam. However lighter shoes could help with this, and it’s possible an amped-up rocker in the shoes could as well. A higher cadence–more footsteps per minute–obviously contributes to faster running, especially since her stride length doesn’t seem shorter, though with the differences in the video angles between the two years that’s hard to measure. If anything, her stride length almost looks longer than before.
Overall it’s clear from changes in Assefa’s form that her shoes were affecting her differently from last year’s shoes, and given the magnitude of her world record it’s pretty unlikely that effect was negative. I can’t put a number on the benefit she got from them, but it looks real to me. Sadly, that means I don’t know who got the world record: Assefa or Adidas.
Wondering who I am and how I’m qualified to do this analysis? Read this.