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adidas Ultraboost 21 Multiple Tester Review

David: Adidas Boost has been an integral part of the midsole game for Adidas for many years now. Some could argue that Boost was the first "new generation" foam to arise in a time when everyone was making EVA the standard foam for running shoes. Now we are in a time of PEBAX or EPU type foams that are also reducing weight and keeping responsiveness. Ultraboost over the years seemed to transition from a daily training option gradually more into the lifestyle lane, but the Ultraboost 21 is different. This is most definitely a running shoe with great durability and protection. The shoe features their new torsion system LEP that increases forefoot rigidity. There also is a new upper material feature  called PRIMEBLUE made from recycled Parley Ocean Plastic and also uses no virgin polyester.

Specifications (per Running Warehouse)
Weight: 12.5 oz / 354 g (men's size 9) 11.7 oz  / 332 g (women's size 8)
Measured Weight Men's Size 10: 13.5 oz / 383 g
Stack Height: 33 mm / 23 mm
Drop: 10 mm
Classification: Premium Maximalist Daily Trainer


Matt: The Adidas Ultraboost 21 is a serious move forward for the series. Featuring an aggressive LEP torsion system, and incredible amount of boost and a snug socklike PRIMEBLUE (primeknit?) upper. A surprisingly responsive shoe that rides far lighter than it weighs, this is a protective but slightly aggressive ride. With a rockered platform due to a stiff but snappy toe off, this shoe can still move if you push it. However the Ultraboost 21 is best for long runs, easy runs and occasional fartlek workouts when you want something snappy with a ton of protection.

The Adidas Ultraboost 21 continues upon the long lineage of boost midsole trainers from Adidas. The shoe utilizes a new LEP torsion system that helps stabilize the sheer amount of boost midsole while also increasing responsiveness. The shoe features 6% more boost through the heel and the shoe provides great protection on foot. The upper fits very sock like and utilizes recycled Parley Ocean plastic with no virgin polyester. 


Matt: The Ultraboost 21 fits me very try to size if slightly short in my my normal men's size 10. There is a decent amount of room throughout the shoe, but the PRIMEBLUE upper is very low volume and fits very closed to the foot. The upper does stretch and needs a few runs to break in. Once it does, it feels more sock like in a customized way. Just know it takes some time. The fit is a bit wider despite the low volume, but does stretch in the midfoot and forefoot. With the 3D heel frame, the heel fits fairly a little tighter initially then opens up. With the one piece upper, I wondered if I actually needed to lace the laces, which prompted me to take them off and run without them. What I found is that the laces connect with the three stripes logo to improve lockdown further around the midfoot. So don't take them off because the fit is better with that lockdown. There is no tongue as this is a one piece upper and there is no last eyelet to lace lock the shoe. The 3D heel frame is similar to previous models, where two external heel counters sit on either side of the heel while the Achilles tendon is left untouched. I do like this modified version as it will provide a high level of medial and lateral stability (more on that later) without direction pressure on the Achilles insertion. So overall this upper is very secure with a snug primeknit upper that still has enough width in the forefoot and midfoot (which stretches with time) and a snugger fit in the heel. I have not tried this shoe sockless secondary to how stiff the 3D Heel frame was.

The Ultraboost 21 fits very much like a snug sock. The ride is snug throughout but still very adaptable to the foot. The upper has a lot of stretch to it but is reinforced well through through the midfoot and lacing system. When you first put them on it almost feels like you do not need to lace it up, but the laces help with better lockdown. The lacing system consists of a plastic 3 stripe overlay that hugs the foot well. The upper is also constructed of recycled Parley Ocean Plastic. 75% Primeblue yarn and 50% textile. The shoe does fit true to size and perhaps a tiny bit long, but this works well with swelling and how snug the upper is. There is a modified heel counter present where the counter is not on the Achilles tendon itself but wraps along the medial and lateral aspect of the rearfoot. The result is an incredibly comfortable and stable heel for such a minimal upper design.


Matt: The Adidas Ultraboost 21 has a very soft feel in the rear and a stiff and more responsive ride up front. The whole shoe takes a few miles to break in and is initially firm for a shoe with so much Boost. As it breaks in, the heel softens, but the forefoot, thanks to the LEP system, remains firm and snappy. This is a bit of an odd sensation at first, but once the pace picks up the shoe rolls along nicely. The Ultraboost 21 is very rockered, with a significant heel bevel and toe spring. The bevel in the heel is fairly aggressive. Heel landings combined with the soft Boost are very cushioned, soft and smooth once the shoe breaks in. This is a great shoe to put on when your legs are beat up and you are landing much farther back. The transition from the heel and into the midfoot and forefoot is extremely smooth and snappy. Those who land up front or a little more forward from the heel will be rewarded with a super smooth and snappy ride that makes the shoe feel way lighter than the measured weight. The LEP system transitions the foot very quickly into toe off and feels like a stiff plate. As mentioned, the forefoot is fairly firm unlike the rest of the shoe. Landing there is a bit surprising as you would expect a much softer ride. However, the LEP system really firms that area up. The toe can be a bit stiff given the LEP system and firmer ride. There is plenty of toe spring however to help with a transition forward. There is a 10mm drop, but I did not notice it as the rearfoot Boost compresses an incredible amount when you land back there. Heel strikers will feel that the drop is lower given the compression, while forefoot strikers will feel it is at 10mm given that the forefoot does not compress. The Ultraboost 21 works best for long runs, easy runs, recovery runs and some shorter uptempo intervals. This is a great shoe for days when your legs are beat up and you want some solid heel cushioning. Despite the weight, the shoe runs much lighter than it physically weighs. It is snappy enough with the LEP and Boost that I have been able to use it for some shorter casual fartlek workouts, but I would not use it for anything longer or faster. The outsole and Boost are both incredibly durable. I have almost 40 miles on my pair and haven't even made a dent (which is a big deal for me). I expect this shoe to last well beyond the normal 300-500 miles.

The Ultraboost 21 has a unique ride for a shoe that has so much boost. The shoe surprisingly runs pretty firm throughout, but still very protective. This is in large part due to the LEP torsion system that they placed into the shoe. The LEP looks almost like a plastic plate running through the midline of the shoe through the midfoot that branches out into a U through the forefoot. The result is a firmer, snappier, and surprisingly stable toe off through the midline of the shoe. The heel has 6% more boost as well. The heel is beveled really well for having so much foam and the transition from heel to midfoot is a lot smoother than I thought it was going to be. The big thing with this shoe... it is really heavy. Like really heavy. This is a shoe that I really only use on recovery days that are really easy with no regard for pace. The components to push the pace a little bit are there, but the weight definitely makes a little bit difficult with getting a heel lift when running fast. I honestly would like to see Adidas do a similar model as the Ultraboost but with less heel stack and keep the LEP system, essentially revamping the original Adidas Energy Boost training models.


Matt: The Adidas Ultraboost 21 is a neutral shoe, but is extremely stable. The upper locks the foot down really well, especially through the midfoot. The platform/last is extremely wide and stable both in the heel and forefoot. The LEP system stabilizes the midfoot and forefoot extremely well. The forefoot, with the wider last, firmer ride and LEP system, also has medial and lateral flare, making it extremely stable. The rockered sole also does a great job guiding motion. The toe off is snappy and the heel bevel is placed a little more laterally to guide motion in. The 3D heel frame provides a great lock down (without pressure on the Achilles) and resists both medial and lateral motion extremely well. This is both a heel counter and significant sidewalls as it continues into the midfoot. There is enough stability as a road shoe that even those with moderate stability needs will be fine in this as long as you don't want a post. It should be noted however that this is a road shoe and does not have the traction for anything but light well groomed trails.

For having so much Boost the Adidas Ultraboost 21 is really stable. The upper locks down well despite having some stretch to the knit. The LEP system stabilizes the midfoot and toe off really well. There is a full contact outsole present. The shoe has a bevel that is integrated pretty well in the heel. Overall the platform is pretty solid for having so much stack height and boost. The shoe does lose some stability in uneven and unstable terrain such as choppy trail or slanted trails/road since there is some give to the upper. It does not cause enough irritation for the shoe to be a deal breaker but you can definitely feel some translation at the foot.


David: Adidas is doing something interesting with the Ultraboost line and I want to highlight that today. Adidas made the decision to change up the torsion system that is famous in many of their performance models. What does this do and why is it important? The new torsion system is a rigid platform they are calling LEP. The aim of LEP is to create a snappy toe off and responsive forefoot (per Adidas website) while still stabilizing the foot through the midfoot and forefoot transitions. If you look from the plantar aspect of the shoe at the LEP system you can see its influence on geometry. Ultimately it is shaped pretty similar to a "H" but a little bit more sleek and streamlined. The LEP begins near the rearfoot/midfoot transition and is present all the way through the forefoot. The torsion hugs the midline of the foot near the rearfoot and widens out along the medial and lateral aspect of the forefoot. What this does is provide a sense of guidance and snappiness through the forefoot. A similar design that I have seen before with this is the Karhu Synchron 2020 or the Skechers Speed Elite. Adidas seems to have streamlined it a little bit better but the roots and concepts are still there. This keeps the midline of the forefoot and heel cushioned but not overly stiff. They almost act as crash pads while still having rigidity and stability along the sides of the shoe. Adidas did this quite well, for the shoe rides pretty firm and stable for having so much Boost midsole. The ride is still very protective, but guided pretty well throughout.

Matt: Although the LEP is a bit stiff for a training shoe, I very much like the design. The old torsion systems that many companies used that just sat in the midfoot are borderline useless. The ligaments and passive stabilizers of the foot, are not just located in one area. They span the length of the foot. So having a midfoot piece that extends out into both the medial and lateral heel and forefoot stabilizes the entire foot so much better. I have voiced many times that I love the older Adidas racing models that had the extended torsion system into the forefoot. Not only does the LEP extend like the old Adios models, but it actually comes up into the midsole on the medial and lateral side. This provides additional stability for the forefoot in BOTH directions, not just biasing in one way. I am really impressed overall that Adidas was able to take a shoe this heavy (my size 10 is 13.5 oz!) and make it feel so much lighter. The Boost and LEP work very well together, combined with the rockered sole, this shoe is very efficient and guided.


Matt: I have and continue to enjoy running in the Adidas Ultraboost 21. However, there are a few suggestions I would like to make. I would consider redoing the toe spring at the forefoot. I think the forefoot may be a bit too stiff for a training shoe. So either the very end of the forefoot needs to have a bit more curve, or there needs to be a tiny bit more flexibility up front. My other suggestion is to consider dropping the weight a little. While this shoe runs much lighter than the listed weight, 13.5 ounces for my size 10 is heavy. I think Adidas would be fine to reduce some of the Boost, as there is still plenty of midsole there. My final suggestion would be changing how low the height of the upper is. This almost makes the shoe feel short and I think a bit more flexibility would be nice. However, this will need to be compensated by with additional lockdown from the laces.

This recommendation has probably been played out time and time again but I think the shoe can reduce its weight. I like the updated LEP torsion system and I think that gives a lot of life to this shoe, but the 6% more boost was not necessary. If they could get this shoe in the 12 ounce region I think the ride would be much more enjoyable. The upper was also really snug through the dorsum of the foot even without lacing, so I think they can introduce a little bit more volume in that region and then work the lacing system in to lock it down without making it feel too snug.


Matt: The Adidas Ultraboost 21 is a high stack height, rockered, sock like fitting maximalist shoe with a snappy forefoot and a super cushioned heel. Those who want a very stable and cushioned trainer without a post will do well in this shoe. Those who want a recovery and long run day shoe that is snappy enough in the forefoot to perform short pick ups will also like this shoe. There is plenty of room width wise in the upper, just be aware the the height is very low. The PRIMEBLUE upper fits very low but provides a decent amount of width. This may make the shoe feel slightly short for some people, but the upper does stretch with time (bonus points for being 75% recycled material). I highly suggest not letting the weight fool you as the shoe moves very well. I am impressed with what Adidas has done here and look forward to seeing what the rest of the 2021 line looks like (I am super excited for the Boston 10).

The Adidas Ultraboost 21 is a high stack really protective shoe that has a surprisingly firm and snappy ride to it. The shoe does run on the heavy side and works best for easy recovery days for me where pace is not of the issue. The shoe does feature recycled materials in the PRIMEBLUE upper with recycled Parley Ocean Plastic with 75% recycled yarn and 50% textile. The shoe fits like a snug sock throughout. For those that love maximum stack height and protection with a neutral ride with hints of stability this is a shoe definitely worth looking into. 



Fit: B (A secure sock like fit. Plenty of room width wise but a bit too low volume/height)                     
Performance: B+ (Runs much lighter than it weighs. Very soft heel and snappy forefoot. best for recovery runs/long runs, a bit stiff through the forefoot though) 
Stability: A- (Very good stability for a supposedly neutral shoe, especially in the forefoot) 
DPT/Footwear Science: A- (Very stable design for a neutral shoe. 3D heel counter also provides high level of stability without pressure on Achilles, forefoot is a bit stiff though) 
Personal:  A- (I really like this shoe. It is stable, cushioned yet I can move a bit in it. Wish it was a bit lighter though) 
Overall: B+ (The best Ultraboost I have tried. Great fitting upper, smooth ride for easy runs, while still able to pick up the pace for shorter distances)         

Fit: B (The upper fits really nice throughout, but is too snug through the dorsum of the foot, especially with having a lacing system)                    
(Very protective and firm ride, VERY heavy, a tad unstable in uneven footing, overall pleasant though) 
(Good stability for how much foam there is, LEP system helps, but still has some give to the upper and midsole in sharp turns or uneven surfaces and conditions) 
DPT/Footwear Science:  
A- (Adidas did a good job with stability integration and responsiveness integration with LEP and the bevel design with so much Boost) 
Personal:  B
 (The shoe does have a pleasant ride, but it is just really heavy, a little unstable in uneven surfaces, but does double really well as a lifestyle shoe as well) 
Overall:  (Smooth and stable for such a high stack shoe with so much Boost, really heavy, upper security is ok but has too much pressure over the dorsum of the foot, overall a good shoe though)      


Chief Editor Matt Klein answers some of your questions about the Ultraboost 21.


Interested in purchasing the Adidas Ultraboost 21? Visit Running Warehouse here. Using this link helps support our work at Doctors of Running! Thank you so much.

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Rabbit Running Clothes:
Incredibly soft, high quality clothing for your next run
Feetures Socks:
Massively grippy socks that will make you feel more one with the shoe
UltraAspire Fitted Race Belt:
Fantastic fitting belt that's durable, quick-drying, and comfortable
Trigger Point Foam Roller:
Help get those knots out post-run and feel better for tomorrow
Coros Pace 2 Watch:
Excellent watch for various running goals and a massive battery life
Theragun Massager:
This small version is great on the go for working tired legs


Karhu Fusion 2021
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Skechers Razor Excess - Light, smooth trainer for everyday and long run miles
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Thanks for reading!

Dr. Matthew Klein is a 140 lb male with notable PRs of 14:45 for 5k and 2:32:44 for the full marathon.  He typically runs 70-100 miles per week and trains at a variety of paces from 8min per mile recovery runs to 4:40 per mile 1k repeats.  He prefers firmer and responsive shoes with snug heels and medium to wide toe boxes.  He is particular to less cushioned shoes and close to the ground shoes, but can handle a little cushion when he gets beat up. IG handle @kleinrunsdpt

Dr. David Salas is a 135 lb male with notable PRs ranging from 3:54 in the 1500m to 1:08:36 for half marathon. He typically runs 60 to 70 miles per week and trains from about 7:30 recovery runs to fast shorter efforts at 4:30 pace. He normally prefers neutral shoes with a firmer ride, but is completely open to other types of shoes.  He is a footwear enthusiast at heart and will always appreciate a high quality shoe when it comes around. For updates on training or testing, IG handle: @docsofrundavid

Dr. Brown is a 155 lb male with notable PRs of 18:18 5K, 39:25 10K, 1:29:01 half marathon, and 3:54 marathon. He typically runs between 20-40 miles per week at a variety of paces from 7:30-8:30 min/mile for recovery runs to 6-6:45 min/mile for tempo runs. He typically prefers shoes that provide some cushioning underfoot but still maintain a more firm and responsive feel. Current goals for 2020 are to break the 1.5 hour half marathon and 3:30 marathon. IG handle: @nate.docsofrunning

Editor's Note: As always, the views presented on this website belong to myself or the selected few who contribute to these posts. This website should not and does not serve as a replacement for seeking medical care. If you are currently injured or concerned about an injury, please see your local running physical therapist. If you are in the Los Angeles area, I am currently taking clients for running evaluations.

Doctor of Physical Therapy
Board Certified Orthopedic Clinical Specialist
Fellow of the American Academy of Orthopedic Manual Physical Therapists

Nathan Brown PT DPT MS
Doctor of Physical Therapy 
Masters in Anatomy and Clinical Health Science
Movement Performance Institute Certified in Advanced Functional Biomechanics 

David Salas PT DPT CSCS
Doctor of Physical Therapy
Certified Strength and Conditioning Specialist

Bach Pham MS
Marketing and Social Media Manager
Master of Arts in Cultural Anthropology

***Disclaimer: These shoes were provided free of charge in exchange for a review.  We thank the  people at Running Warehouse for sending us a pair.  This in no way affected the honesty of this review. We systematically put each type of shoe through certain runs prior to review. For trainers and performance trainers, we take them on daily runs, workouts, recovery runs and a long run prior to review (often accumulating anywhere from 20-50 miles in the process). For racing flats we ensure that we have completed intervals, a tempo or steady state run run as well as a warm up and cool down in each pair prior to review. This systematic process is to ensure that we have experience with each shoe in a large variety of conditions to provide expansive and thorough reviews for the public and for companies. Our views are based on our extensive history in the footwear industry and years testing and developing footwear. If you are a footwear rep looking for footwear reviews or consultations on development, we are currently looking to partner with companies to assist, discuss and promote footwear models. Partnership will not affect the honesty of our reviews.

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