Nike Ultrafly: ZoomX for the Trails
By Matthew Klein
As road shoe technology has progressed and with the advancements from super racing shoes coming to trainers, it has now extended into the trail running world. While plates were already present in various forms as rock plates, new combinations of plates and super foams for Trail have been hitting the market. The Nike Zegama was one of Nike's early trail shoes to use ZoomX foam but it functioned as a training and long-distance shoe rather than a racing one. Meanwhile, Saucony and the North Face have had their super trail racing shoe models (Endorphin Edge and Summit Vectiv Pro) out for some time for enough people to test and see what happens when super racing shoe technology hits softer surfaces. The company known for its racing shoes has not-so-quietly been waiting and demoing its newest trail super shoe at a variety of elite ultramarathon competitions. The Nike Ultrafly is finally coming to market after being seen under the surface for so long. A true ultramarathon trail super shoe rather than a short-distance one, the Ultrafly is a unique niche shoe that blends super foam and plate for both long-distance training and racing.
Nike UltraflyPrice: $249.95 at Running Warehouse
Weight: 10.6 oz, 300 g (men's size 10), 8.8 oz, 249 g (women's size 8)
Stack Height: 38.5 mm / 30 mm
Drop: 8.5 mm
Classification: Long/Ultra Distance Trail Racing Shoe
RUNNING SHOE SUMMARY
The Nike Ultrafly is a super trail racing shoe for ultramarathon and long-distance training and racing. The upper features a thin but secure mesh with a wider toe box, lower volume fit, and secure midfoot/heel. The midsole is soft and bouncy ZoomX foam with an additional outer layer that protects the foam from debris. A carbon fiber Flyplate sits in the midsole and provides a surprisingly smooth transition at a variety of places and stabilizes the shoe decently well. Finally, a new Vibram outsole provides traction and durability over longer miles. The Ultrafly Trail is not a short-distance racer and instead excels as an ultramarathon racer that provides maximum comfort and efficiency over any adventure ahead.
SIMILAR SHOES: Saucony Endorphin Edge, The North Face Summit Vectiv Pro
FIT
The Nike Ultrafly fits me true to size in my normal US men's size 10. The volume is quite low although the width is different. The heel and midfoot fit normal to slightly snug while the forefoot is on the wider side. The mesh material, while sitting low, does have some stretch upfront, which provides a comfortable amount of room without being sloppy. The tongue is thin and wide with some central padding. An internal gusset connects to the tongue on both sides and secures the foot down well. The heel features a flexible heel counter and a moderate amount of heel collar cushioning. I had no issue with the heel counter and only those with extreme sensitivities will have issues. The security has been fairly good. I initially had some mild heel slippage but tightening down the laces a little helped. I did not have to lace lock the shoe and found even on strong turns I was fine.
The mesh material does a great job of keeping material out. I have taken these through water and my feet did get wet. I have not gotten the chance to take them through mud as it has been too dry in SoCal. The upper is thin enough it won't keep wet material out but it will keep dry stuff out. This makes it excellent for dry trails and basic water crossings like you will see in dry hot climates. In more muddy climates it may be more challenging, although I still need to confirm that.
This is one of the few trail shoes I have felt comfortable wearing sockless. I have run up to 10 miles (my max right now) without socks and had no issues with chaffing. Those taking these for ultramarathon distances will most likely need socks but those using them for short distances will have a well-fitting upper that sits comfortably even against bare skin.
PERFORMANCE
The Nike Ultrafly is an ultramarathon super trail racing shoe. It features a full-length midsole of ZoomX encased in a thin film that protects it. A full outsole of Vibram rubber runs the length of the shoe, providing durability, traction and firming the ride up just slightly. This is not a Vaporfly for the trail as it sits at 10.6 oz (men's size 10) and while the ZoomX is still there, it is more controlled than its road racing cousin. The midsole does feel comfortable underfoot even after long miles and long periods. While I am not doing high mileage right now, I have done double runs and worn this shoe all day. The secure upper with the wider toe box and soft ZoomX do a great job at providing all-day comfort. There is an 8.5mm drop, which I did not find noticeable due to the compression of the midsole.
The weight is not noticeable as a long run and training shoe but is noticeable when picking up the pace. This is not a short-distance racing shoe, instead a smooth-riding long-run and ultramarathon racing shoe. I have done workouts, including hill repeats and a few tempo runs, and found short sprints were fine due to the traction but longer fast sustained efforts were a bit more challenging. Uptempo and steady efforts are where this shoe shines repeatedly. Across steady terrain, it is a smooth rider that glides over road, well groomed and moderate trails. The Vibram outsole is durable enough to handle roads as every run I have used this shoe for has been door to trail. I have 45 miles on my pair and there is barely any wear on the outsole. The lugs are mild but works well with the Vibram outsole on mild to moderate trails. They are not deep enough to be completely secure on unsteady soft trails but do fine on everything else.
STABILITY
The Nike Ultrafly is a neutral trail shoe. There are no traditional elements of stability. There is sole flare in the heel and forefoot that creates some inherent guidance. The additional torsional rigidity of the plate adds some resistance to movement at the heel and forefoot. The midfoot is quite narrow, although is offset slightly by a higher medial arch. This combined with the softer ZoomX makes this a neutral shoe. The heel and forefoot have mild guidance but the midfoot is fairly neutral, making it a option for those that need mild guidance up front and behind over moderate mileage but the midfoot will work best for those with neutral mechanics.
Thoughts as a DPT: Footwear Design For Ultramarathon Distances
By Matthew Klein
Running economy or running efficiency can be influenced by a variety of things in different individuals. We know some people respond differently to different levels of shoe stiffness (Mcleod et al. 2020). We also know that while there is variation in response to shoe softness, one of the biggest impactors on the running economy in super shoes is the special foams (Dominy & Joubert, 2022; Nigg et al., 2021; Ortega et al., 2021). There is also the matter of weight. What is seen on the roads was that super shoes not only have optimal stiffness and special cushioning, they are also incredibly light. Road shoe are typically lighter than trail shoes given that all you need is a mild outsole for durability but do not need extensive protection against the elements. The design of trail shoes is quite different. Additional traction is needed to provide grip on a variety of surfaces. Additional protection is also needed at all levels of the shoe due to the various hazards that are present in trail running that are not in road running.
The evidence on weight and economy is generally that for every 100g less a shoe weighs, there is a 1% improvement in economy (Franz et al., 2012). However, there is a ceiling effect to this where economy starts to worsen due to decreased cushioning and the need for muscular effort to shift toward shock absorption rather than propulsion.
Recent developments in foam technology have added another factor. Softer, more resilient foams have been shown to improve running economy (Worobets et al., 2014). In the road racing world, the combination of lightweight and super-resilient foams have been combined. In the trail racing ultramarathon world, there are far more variables at stake, making for a trade-off of protection vs lightweight.
The Ultrafly is a shoe specifically for ultramarathon racing. It has a moderately rockered sole, softer resilient cushioning that is bouncy but not too mushy. It has a durable grippy outsole that provides protection from the elements and security on most terrain. The toes are kept in a neutral position and the toe box is wider to reduce irritation but the hold is still secure. Designing a shoe like this requires some modifications and sacrifices. For a shoe to last during a 100k to 100-mile race on varied trail, some weight will need to be added to improve traction and durability. Without the weight from the outsole, this would be a far lighter shoe but it would not be as protective and durable for trail terrain. Designing certain components of a shoe always revolves around balance the needs of those using this tool. While it may not be efficient for shorter-distance races, the additional weight is probably a fair trade-off for the durability and ruggedness needed to handle long-distance trail racing.
Sources:
Dominy, Trace A. and Joubert, Dustin P. (2022) "Effects of a Carbon-Plated Racing Shoe on Running Economy at Slower Running Speeds," International Journal of Exercise Science: Conference Proceedings: Vol. 2: Iss. 14, Article 15.
Nigg, B. M., Cigoja, S., & Nigg, S. R. (2021). Teeter-totter effect: a new mechanism to understand shoe-related improvements in long-distance running. British Journal of Sports Medicine, 55(9), 462-463.
Ortega, J. A., Healey, L. A., Swinnen, W., & Hoogkamer, W. (2021). Energetics and biomechanics of running footwear with increased longitudinal bending stiffness: a narrative review. Sports Medicine, 51(5), 873-894.
RECOMMENDATIONS
There are a few suggestions I have for the Ultrafly Trail despite it being an excellent ultramarathon racer. Given its function as a long-distance shoe, I would like to see the midfoot filled in for inherent guidance over unstable terrain and longer efforts. While the ZoomX foam and heel bevel offsets this a little, the posterior flared midsole could be reduced for weight purposes. I understand arguments may be made for it as a rudder during descents. I personally would get rid of it as it offsets a natural heel rocker that may be more efficient for some people. Finally, this may take some unique geometrical alterations but I would like to see the weight reduced. This is the heaviest of the "Trail Super Shoes" and the higher weight limits its versatility for shorter distances. While it is durable, for $250 I expect the same versatility found in the Vaporfly. The Ultrafly works far better for training than the Vaporfly, but that price tag is challenging for such a niche distance shoe.
WHO THIS SHOE IS FOR
The Nike Ultrafly is for those looking for a ZoomX, plated shoe for long runs and ultramarathon racing on varied, mild and moderate trails. Those wanting a normal-fitting heel/midfoot with a wider forefoot that sits lower will enjoy the fit. Those wanting ZoomX foam with a plate that feels comfortable at both easy and uptempo paces will enjoy the ride. This is a neutral riding shoe, so those with neutral mechanics and stable lower limbs will do best but it isn't so unstable that those wanting a moderate distance training shoe won't be able to use it. Those expecting a Vaporfly for the trails will be disappointed as it is quite a bit heavier and geared towards ultramarathon/steady efforts. It does bring super shoe technology to the trail from Nike but functions better as an efficient shoe rather than a super light and fast one. It does also uniquely feels comfortable and natural for training paces and is not something I would necessarily save only for races.
With the $250 price tag I would expect to get a ton of miles and use out of this shoe beyond just racing. I still think this shoe needs to drop a little weight or a Vaporfly trail needs to come out. All the cross-country high school/college runners would love that and may be disappointed to hear the Ultrafly doesn't fill that gap. The ultramarathon community however should be excited that they have a super shoe specifically designed for them. So Nike did not miss the mark but adjusted the target and did a pretty solid job in the process.
GRADING
Matt
Fit: A- (Wider toe box with lower volume fit and normal width heel/midfoot. Mild heel slippage fixed with tightening laces)
Performance: B+/A- (Excellent long run and training shoe. Can handle uptempo and all day efforts but limited versatility into faster efforts)
Stability: B/B+ [Neutral] (Inherently stable forefoot, mildly so in heel with neutral/narrowed midfoot)
DPT/Footwear Science: B+ (Solid design for ultramarathon shoe, however weight limits versatility into shorter distances and may wear on many more than a $250 price tag should allow)
Personal: B+/A- (My go to shoe for training on trails but would pick other things for racing given that I stick to 5k to half marathon even on softer surfaces)
Overall: B+/A-
SHOP | SUPPORT DORNike UltraflyPrice: $259.95 at Running Warehouse
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FURTHER READING: TRAIL SHOES 2023
Brooks Catamount 2 - A redesign adds a SkyVault plate to the trail shoe
Brooks Divide 3 - A surprisingly solid trail runner at $100
Hoka Challenger ATR 7 [Stable Neutral] - This road-to-trail comes in at its lightest yet with a firmer rolling ride
Hoka Tecton X 2 - Subtle changes keep this trail racer a fun and fast ride
Hoka Zinal 2 - Hoka's super light trail runner gets an update
La Sportiva Cyklon Cross GTX - Winter ready running in every way possible
New Balance Fresh Foam X More Trail v3 - A real balance of cushion and durability for the trails
Salomon Glide Max TR - A new max cushion trail entry from trail specialists, Salomon
Salomon Glide Ride 2 - A solid moderately stacked trainer for the trails
Salomon Pulsar Trail Pro 2 - A fast, aggressive trail shoe that has one setback that holds the shoe back
Salomon Sense Ride 5 - A lower cushion, well-riding trail shoe that can do a bit of everything
Saucony Blaze TR - Surprisingly light trail running for $100
Sauocny Endorphin Rift - A flexible, light, PWRRUN PB-fueld trail runner
Saucony Peregrine 13 (and ST) - The lightest, yet also most cushioned model in the trail line
Saucony Xodus Ultra 2 [Stable Neutral]- A great trail runner becomes even better. Lighter, better fitting, and fun
Topo Athletic Terraventure 4 - An excellent walking, hiking option for runners and hikers alike
Find all Shoe Reviews at Doctors of Running here.
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