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Nike InfinityRN 4: What is This Again?
By Andrea Myers and Matthew Klein

The Nike Infinity series has an odd history. During its debut, it was advertised as a shoe that would reduce injury thanks to a small (poorly run) study comparing injury rates in neutral runners using it compared to the Nike Structure (which previously was not a shoe for neutral runners). I (Matt) have discussed the issues with this extensively so I will not continue to hammer away. What the Infinity series really came out as was a highly rockered daily training shoe with a heel clip that provided some mild guidance in the back. Version 3 was finally the one that both Andrea and I actually enjoyed. The rocker was just right, the fit improved and the midsole was right where it needed to be. Of course, Nike decided to change everything and now we have the completely new Nike InfinityRN 4 (Infinity Run?). The RN 4 brings the Infinity series to the fully maximal realm. A new knit upper provides the space we asked for while a TON of ReactX sits underfoot provides a cushioned and rockered ride for mileage. Despite the changes, it maintains some of its original purpose.

Nike InfinityRN 4
Price: $159.95 at Running Warehouse
Weight: 11.1oz, 314g (men's size 9), 9.4oz, 266g  (women's size 8)
Stack Height: 39mm/30mm
Drop: 9mm
Classification: Daily Trainer


Matt: The Nike InfinityRN 4 is a highly cushioned, maximal daily training shoe for easy and daily mileage. A huge amount of Nike ReactX sits in the midsole, providing more cushioning and a little more bounce than prior React foams. The upper is a wonderful knit that does fit a half-size small (go up a half size) but with correct sizing provides a secure fit with a more accommodating fit. Now featuring some well-integrated sidewalls and a unique lateral geometry, the Infinity RN is the closest of the entire series to Stable Neutral. A heavy but well-cushioned and rockered shoe, the InfinityRN 4 will appeal to those that want a Nike shoe with a ton of cushioning for easy and recovery-paced mileage. 

The Nike InfinityRN 4 is a complete redesign of the Infinity Run line. It now features Nike's ReactX midsole foam, which Nike states provides 13% more energy return as compared to the React foam used in previous versions. Nike also states that ReactX has a 43% lower carbon footprint as compared to React foam. The intrusive arch support and heel clip of previous versions is pared down in v4, and the slightly greater midsole stack (+4mm in the forefoot and +5mm in the heel) does make v4 more protective as compared to previous versions, although the ride is definitely on the firm side. The redesigned Flyknit upper is more accommodating as compared to v3, although I would have liked a little more structure in the forefoot, especially at faster paces. The InfinityRN 4 will be a nice daily trainer for runners who prefer a firmer ride.

: Adidas Solar Boost 5
PAST MODELS: Nike Infinity Run 3


Matt: Nike sent us a 1/2 size up from our normal size and I would highly recommend doing the same. My men's size 10.5 fit me exactly the same as a normal men's US size 10 usually does. The InfinityRN fits a half-size small, so definitely go up a half-size. The Flyknit upper is soft, flexible, compressive (like a sock) and a little thick/warm. The fit is normal throughout with an extremely low forefoot. The Flyknit upper does stretch but really low and compressive across the top of the forefoot. Despite this, I can still wiggle my toes and spread them a little. The midfoot fits normal with a strongly gusseted tongue. This provides plenty of lockdown and I did not have to lack lock the shoe or tighten down the laces. The heel fits normal in width with a fairly flexible heel counter and a large amount of heel collar cushioning. There is a counter (I had to double-check) but it is highly flexible and did not bother me at all. The extra padding around the heel collar almost made the heel feel snug and further lock the foot in. I have tried this shoe sockless and while it can handle it, the warm upper does lend to sweaty feet. So if you are not in hotter climates, that might work for you (I'm in SoCal in the summer where it isn't working).

Nike recommends going 1/2 size up in the InfinityRN 4 and sent me a women's 10 instead of my usual women's 9.5. I would wholeheartedly agree with their recommendation, because the 10 fit perfectly true to size, so the 9.5 would have definitely been too short. The Flyknit upper is soft, flexible, and on the thicker side, which made it a little less breathable than I would have preferred in the summer heat. The tongue is thicker where it sits on the dorsum of the ankle, while the part closer to the toes is thinner and made of the same Flyknit material as the rest of the upper. Nike references a "Flyknit fit band" in their description of the shoe, which appears to refer to the gusseted tongue, which is Flyknit and does feel like it provides some extra midfoot support. There is also a lace loop on the middle part of the tongue, and I was pleased that the tongue stayed securely in place during all of my runs.

I have always loved Flyknit because it never gives me hot spots on my 1st or 5th MTPs, and the InfinityRN 4 is no exception. The upper is comfortable and accommodating, but does feel a little loose when running at faster paces. The flat laces are on the thinner side and have mild stretch. I found the shoe easy to lockdown and did not experience any heel slippage. The thin tongue does lend itself to potential dorsal foot irritation from the laces, so I was careful not to overtighten them.The heel counter is semi-rigid in the lower half, flexible in the upper half, and has ample padding internally. The medial longitudinal arch support in the shoe is noticeable, but not nearly as intrusive as v3. The arch support did break in after about 20 miles and is now only minimally noticeable.


Matt: The Nike InfinityRN is a daily training shoe for easy and recovery miles. The weight is over 11 oz now (men's size 9) and it is noticeable. This may be due to the taller stack height, which provides far more cushioning underfoot than the previous versions. The ReactX is not bouncy at all but feels far more protective and moderately compliant. It compresses decently but does not give anything back. I would say it is between cushioned and firm, balanced somewhere in the middle. Combined with the heavier weight, the InfinityRN is not a good choice for anything but easy and plodding miles. I have only used this shoe for easy runs up to 1 hour and found them comfortable for that. they were a bit too heavy for me to go beyond that and have continued to serve as a recovery day/moderate distance easy run shoe.

The ride of the InfinityRN is highly rockered with fairly smoother transitions. There is a large heel bevel that has a unique compressive geometry on the lateral side. This makes for an adaptive posterior lateral bevel if you land there. Despite the heel bevel, the 9mm drop was really noticeable. The heel is quite apparent regardless of where you land. If you like a higher-drop shoe, this is one of the rare high-stack ones. The transition through the midfoot is not significant but the forefoot does have some mild flexibility. There is a mild rocker up front with a little bit of toe spring, making for a smooth and gentle transition through the front of the shoe. The rest of the shoe is fairly stiff, relying on the posterior rocker to get you forward.

Some of the extra weight may come from the thick outsole, which is highly durable. I have 32 miles on my pair with no wear on the outsole. The rubber is fairly thick and features a classic waffle/lugged outsole. This provides fairly good traction on a variety of surfaces and allowed me to take this on mild trails. I would prefer something with more aggressive lugs, but this shoe does have some versatility across a few different terrain. It does best on road and grips well in both dry and wet conditions. The extensive outsole will likely last a long time, which combined with the thick midsole suggests higher-than-normal durability.

The weight, Flyknit upper, and geometry of the InfinityRN 4 make it best suited for easy miles. The shoe is 0.5oz heavier than v3, likely due to the increased midsole stack. I found the ReactX midsole to be firm, but I would agree that it is slightly more responsive as compared to the React foam in v3. The midsole felt very firm and almost dead on my first few runs, but did start to slightly soften up after about 20 miles. Don't let the 39mm/30mm stack height fool you - this is not a max cushioned shoe or even a moderately cushioned shoe. The thick midsole provides protection from the ground, but there is not much compliance. The shoe feels like its stated 9mm drop and I did find the heel to get slightly in the way of my preferred lateral midfoot strike. I still enjoyed my runs in the shoe, but the higher drop and firm ride definitely limited the shoe to easy paces and <1 hour runs. The later forefoot rocker gently rolls the foot into push off without feeling aggressive or unnatural. The shoe has high longitudinal bending stiffness, with only a mild amount of flexibility in the forefoot. The Flyknit upper feels secure when running slowly, but I noticed a looseness anytime I picked up the pace, particularly when going downhill.

The full coverage rubber outsole provides decent traction on wet roads. There is no visible wear on my pair after 30 miles. Like v3, I would expect higher than average durability. 


Matt: I have gone back and forth on this but have finally decided the Infinity RN deserves a Stable Neutral title. There are several newer methods of stability, including a wider sole, sidewalls, sole flare and a unique lateral geometry. The sidewalls in the heel and midfoot are significant and keep the rearfoot centered. This is a higher arch and while not a true stability method does add some extra pressure to the sidewalls. The sole is on the wider side especially in the forefoot. The midfoot does narrow but not as much as previous versions. The forefoot also features a large amount of sole flare in both directions, providing a centered place to transition from. The final unique part of this shoe is the rearfoot geometry. The concave lateral heel collapses more than the slightly convex medial side. If you land laterally, this creates a smooth transition with a little bit of lateral bias. Those who need that will do well and those who do not should not be bother too much given its subtle nature. However those with heavy footstrikes that are sensitive to lateral motion at the heel should be at least a little cautious. Overall, the InfinityRN has a stable heel, somewhat stable midfoot and a centered forefoot. 

The Nike InfinityRN 4 is a good example of a stable neutral shoe. For rearfoot strikers, the sole flare, which is thicker on the medial side, may provide some resistance to early medial motion. The forefoot sole flare is more balanced medially and laterally, which may help center the foot as the forefoot rocker guides the foot into push off. The sidewalls in the midfoot and rearfoot further help to center and stabilize the foot in the shoe, which helps reduce the instability created by the stretchy Flyknit upper. This shoe will work well for runners with neutral mechanics or those who need a shoe with mild guidance features.

Thoughts as a DPT: Nike's Stability Shoes, Without a Post in Sight
By Andrea Myers

Nike introduced the original Infinity Run as a shoe that they said could prevent running related injuries. Unfortunately, they based these claims on a small, poorly designed study that Matt analyzed in detailed [in the Infinity Run 3 review here].

Fortunately, Nike appears to have abandoned these claims with the InfinityRN 4 and the marketing for the shoe seems focused on its upgraded ReactX foam and its higher stack height. Nike also lists the level of support that the InfinityRN 4 provides as "high", the same rating it gives to the soon to be release Structure 25, which they state is their most stable shoe. It is interesting to see shoe companies embracing the idea that stability can encompass more than just a medial post, which is what you would expect to see in a traditional stability shoe. Neither the InfinityRN 4 nor the Structure 25 have a medial post, but both have significant non-traditional stability features that may work well for runners with varying stability needs.

While the Structure 25 is marketed towards runners who need more medial stability, the InfinityRN 4 will work well for runners with more diverse stability needs and is truly a stable neutral shoe. The asymmetrical sole flare in the heel may provide resistance to pronation or slow the rate of pronation. For runners like me who tend to land too far laterally and potentially under pronate, the more balanced design of the sidewalls and forefoot sole flare may help center the foot, while the forefoot rocker guides the foot into push off. I appreciate that Nike includes information about rocker geometry, base width, midsole tuning, and upper security specifically in the "support" sections in the descriptions of these shoes. Stability is about so much more than just posting (as we like to remind our readers on a frequent basis) and it will only benefit runners for shoe companies to continue to expand their marketing and technical descriptions of the stability features of their shoes. This will help shoe companies get the right shoes to the right runners, which will be a win-win situation for everyone.


Matt: I have mixed feelings about the Infinity RN 4 given that I finally was getting along with version 3 when they completely changed everything. There are improvements but I still have a few suggestions. The first is to fix the sizing so runners don't get confused. The upper would benefit from some additional structure in the midfoot. While the lockdown was good and compressive, it only work for easy miles. Attempting to pick up the pace did cause sliding around especially in the forefoot and heel. Picking up the pace was also difficult due to the high weight. If a new foam is being added, I would expect more cushioning and less weight. This felt almost the opposite, where there was plenty of protection from the height but at a cost of being heavier and not as soft as hoped. I would still love to see the same geometry but with far less weight as that may make it easier to get both easy and longer miles in. This could occur with a lower density of the foam or being more strategic with outsole rubber placement.

Andrea: I think the InfinityRN 4 is a nice update on v3, but further improvements could be made. First, Nike should clean up the sizing so that runners can stick with their usual size. The Flyknit upper could benefit from some overlays to provide additional shape and support, which would make the shoe perform better at faster paces. At 11.1oz for a men's 9 and 9.4oz for a women's 8, this is a heavy shoe that provides a firm ride. I would like to see this shoe lose some weight, either by reducing the stack height to that of the previous version or reducing the amount of outsole rubber. 


Matt: The Nike InfinityRN 4 is for those who want a highly cushioned, rockered, higher-drop shoe with a sock-like fit for easy and recovery/plodding miles. The upper is compressive Flyknit that fits well but only secures the foot with slower miles. The midsole is moderately cushioned with a rockered and higher stack, making for a solid transition during easier paces. The weight is still extremely hight, further cementing this shoe for easy efforts. The major positive is that this shoe really becomes stable neutral with the wider base, geometry and sidewalls. This is still a Nike maximal shoe and those that are brand loyal may find it as an alternative to Hoka or other companies max cushioned shoes. The weight still holds it back a little, so those who are not sensitive to that will do best. Those used to the Infinity Run 3 need to be aware that this is a completely different shoe in both positive and a few negative ways. Nike made some major changes and fills a maximal spot that may soon be filled by the Vomero 17. In the meantime, the InfinityRN will do. 

Andrea: The Nike InfinityRN 4 is a stable neutral daily trainer that has a soft Flyknit upper and a firm, rockered ride. Those who liked v3 will most likely find v4 to be a nice update. Runners who need any amount of softness in a shoe should look elsewhere, as this shoe does not provide much give, despite its high midsole stack. Runners looking for a more compliant shoe with a similar stack height may do well with the New Balance More v4 or the Nike Invincible 3 (although that shoe also has upper stability issues). If Nike can stabilize the upper and give the midsole a little more compliance, they may have a real winner for v5...


Fit: B+ (Must go down a half size for normal fit. Flyknit sock-like but has poor hold during major turns and faster efforts)
B (High drop, moderately cushioned plodder. Heavy but rockered. Best for easy miles. )
Stability: B+ [Stable Neutral] (While heavy and a bit clunky, does heel/midfoot sidewalls, forefoot flare and unique lateral heel geometry that eases runners in and keeps them somewhat centered. )
DPT/Footwear Science: B+ (Solid improvements and bonus points for unique lateral geometry. Still needs to be far lighter and lower drop if Nike wants to truly enter the maximal road scene. )
Personal: B- (Solid shoe but too heavy for me to continue using. Nice for casual use. More interested in the new Vomero/Structure)
Overall: B/B+
Fit: A- (must go up 1/2 size due to length, loose Flyknit material unstable at faster paces)
Performance: B+ 
(very firm ride that mildly breaks in after 20 miles, use limited to shorter, slower runs due to weight, firmness, and upper instability)
Stability (stable neutral): A- (good use of sole flare, rocker design, and sidewalls to provide a centered, stable ride)
DPT/Footwear Science: B+/A- (nice improvements on v3, but midsole and upper still need some work)
Personal: B/B+ (improved fit as compared to v3, but high drop and firm ride limit use for me)
Overall: B+


Nike InfinityRN 4
Price: $159.95 at Running Warehouse

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FURTHER READING: Max Cushion Shoes

Adidas Ultraboost Light - The 23rd ultraboost features Light Boost to help cut 2 oz from the trainer
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Brooks Aurora BL - Brooks experimental project offers a look into the future
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Find all Shoe Reviews at Doctors of Running here.

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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.

***Disclaimer: These shoes were provided free of charge in exchange for a review.  We thank the people at Nike 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 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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