Altra Running Impulse Review- A Pleasant Surprise. Fast,Light "Stability" Shoe That Doesn't Run Like One.

By Sam Winebaum

The Altra Impulse is an 8.6 oz 243 gram Men's 9 Zero Drop light cushioned "stability" shoe with a 23 heel/23mm forefoot. $120, on sale now.  I say "stability" in quotes as this term is often associated with the dubious effort to "control" pronation.  All feet pronate to some extent, they are supposed to. The Impulse is actually a great all around shoe, and a fast one, for any type of training and racing for this runner who has always run "neutral" shoes.

Men's Altra Impulse: www.altrarunning.com

I have more than 70 miles in the Altra, most in the last few weeks. Very rare that I run every day in a new shoe or that I accumulate close to 50 miles before I review, but I really dig the energetic, comfortable well directed ride of the Impulse and especially the incredibly well executed "front of the house", the forefoot. The sometimes sloppy Altra Foot Shaped toe box is well held by the asymmetrical lacing. The upper sits on top of a stable and responsive midsole with full contact StabliPod rubber outsole tuned for just the right amount of cushion and flexibility by innovative InnerFlex channels through the midsole. The heel, due to Zero Drop, is firm and a bit low for me an issue easily resolved by training (w)heels. More on this below.
The Impulse will be the first shoe to include Altra's IQ run stride metrics sensor system. See our Outdoor Retailer coverage about the IQ shoe and system here

Women's Altra Impulse: www.altrarunning.com 

The "Issue" of Pronation Control
A bit of "control" of the gait does not have to be a bad thing as we all get sloppy, all feet pronate anyway and helping the foot track in the direction of travel, as the Impulse does brilliantly, is a good thing. How Altra does and does not do the control makes the difference.

• no firm midsole inserts under the medial side mid foot as is the usual. Instead, according to Competitor Magazine a cantilevered  wedge sloping down from the inside to the outside of the shoe to keep the foot from collapsing inward.  If it's there it is not noticeable and it work fine for me. Doesn't overdo the control, just a bit of guidance forward.
• 3 points of firmer well covered outsole contact the StabiPods: heel, midfoot, forefoot. Just the way I like any shoe stable and smooth in transition. So not only a touch of pronation control but supination control for a balanced directed push off.
• a great upper with asymmetrical lacing which for the first time in an Altra does not create a compromise between the roomy Foot Shaped front of the shoe and good secure foot hold.
• a series of holes drilled into the midsole both vertically and as slits horizontally Altra InnerFlex to make the shoe more flexible, soften the forefoot feel a bit and to lighten it.

Upper and Fit
The Impulse fit me a bit large and loose in the heel with thin socks in my true to size before adding my heel wedge training (w) heels. I used a lace lock through the far back last holes to cinch the heel. The upper is made of a very tightly woven soft, light mesh.

There are no seams or overlays beyond the logos at the mid foot and a substantial toe bumper to keep the foot aligned and stable in the roomy upper on push off. Unlike many such toe bumpers, and even the Lone Peak 2.5 from Altra, I have no sense it is there, that annoying feeling of something over the tip of the toe, so plenty of overhead toe volume for me. The asymmetrical lacing which extends the lacing closer to the medial side really keeps my front of foot locked in but with plenty of that Altra toe splay room from the FootShaped toe box.

No sense, as I sometimes have, of a bit of a sloppy forefoot in Altra's Foot Shaped toe boxes, obviously key for a shoe designed to go fast. While a bit "baggy" looking on the foot no sense of a lack of support anywhere except maybe in the heel collar which is wide. A fabulous tongue with just the right cushioning and no side to side slip as I found in the Lone Peak. I think part of the secret, decent friction from the material and especially that the tongue is not free floating side to side very far down towards the toes being attached to the sides at the 3 lace hole. 

The lateral side of the tongue where it attached has a bit of stretch material, the medial side does not to better support the pronating food.  As stated above they fit me a bit large in my true to size but as I tend to "miss" the heel in Altras given their Zero Drop I added a 2 inch long  5-7mm soft piece of yoga mat type material at the heel which gave me some training (w) heels and some extra cushion and drop. The heel wedges also snugged up the heel fit very nicely.  I also tried substituting a variety of after market sockliners such as the Superfeet Carbon and while not a big issue, the foot towards the heel sits a bit higher and the heel collar is a bit wider than I would like in the relatively low heel collar. The heel collar of the Topo Magnifly is better executed in my opinion (review here) as it perfectly secures the rear of the foot even when the road Magnify is used as a trail shoe.

While not a place people usually go looking, the connecting piece between the 2 sides of the upper which is called the Strobel board is not the usual solid glued down sheet but a mesh open to the midsole. Less glue is required, the shoe becomes more flexible, and weighs less. We saw a similar construction in the Spring 2015 Pearl Izumi N2. Upper construction appears solid if a bit rough where the end of the heel collar meets the rest of the upper at the 2nd lace hole and a bit of fuzz around the sewn lace hole reinforcements.


Midsole and Outsole
The midsole is made of 2 layers: underfoot Altra's Abound (yellow) which "reduces the impact of hard surfaces and returns energy with each stride". Not sure what this material is but likely a mixture of EVA and rubber. Underneath the main layer is Altra's Ultralight EVA (crimson) whose firmness I measure at approximately 42C, so a fairly normal midsole firmness.

The midsole is made lighter and more flexible overall and with some give over the firm Stablipods  by being drilled with a series of circles as well as having the 4 InnerFlex side slit channels which go all the way through the midsole.

Altra Impulse Inner Flex and Drill Holes provide drainage

The slits at the front combined with the drilled holes provide drainage from the insole area. When combined with the mesh Strobel board the shoe should drain well, something triathletes often look for. The flexibility is smooth and decent for a 23mm forefoot stack shoe if a touch stiffer than I would like at the very front of the shoe.

The outsole has 3 areas of black harder rubber at the heel, a nice stable landing and push off zone underfoot, and at the medial toe area.  The rest of the outsole is exposed EVA. The heel area seems to have harder rubber than the front 2 areas, the usual configuration for most run shoes with the firmness of both outsole materials about the same as what I find in most shoes. 50 miles in and almost no wear at all with the very fine pattern on the surface visible everywhere even at my high wear point at the heel. Good stuff and a good geometry of the heel construction, slightly beveled to the lateral side with no overhang behind the heel cup which may contribute to the firmness as often an overhang behind the heel softens impact for me.
But these are Altras and we aren't supposed to run on our heels.... and because the Impulse is an Altra, the forefoot feel is particularly fine on the road particularly given that the upper is well secured to the platform if roomy up front. Stable, cushioned and energetic. The 23mm front stack really protects the foot but doesn't deaden the ride or responsiveness. As stated above the heel is firmer, a touch too firm for me, unless going fast and off the heel. This may come from the heel height at 23mm really, at the lower limit in terms of stack for me in any shoe and that this is also a zero drop shoe.  I might compare the heel firmness to the New Balance 1400 or Topo Magnifly.  I added my wedge of yoga mat and am happy as can be. Adding some of those InnerFlex channels in the heel area might help.

Super Pleased with my Altra's at the BAA Half

Update: I ran the BAA Half Marathon in Boston this past weekend in the Impulse. "Official" time 1:40.27. I got a slow bottled up start the first minutes and the course was very curvy and difficult to run the tangents with the crowd ahead blocking view of the road. My Ambit GPS showed 13.3 with pace 7:32 so a touch under 1:39, and one second under my goal pace. Tip: I have found GPS watches generally very accurate on point to point courses with few turns. On courses with lots of turns and or where it is difficult to run or see the tangents they tend to run long. Plan ahead on such courses to run faster than your GPS data to hit a goal.
The Impulse was outstanding: climbed well on the rollers and was particularly effective on the downhills. Officially now replaces my beloved Adios Boost 1 for half racing and I would race a marathon in them for sure.
Update: A week after the BAA Half I ran the very hilly and spectacular Mount Desert Island, Maine (Acadia National Park) Half. 1:38.34 on a very tough course. Impulse was superb on both uphills and the many downhills. My legs none the worse for wear the next day. Impulse now in the lead for my Shoe of the Year.

Conclusion and Recommendations
The Altra Impulse is classified by Altra as a stability shoe but neutral runners seeking a light, stable, fast, well cushioned forefoot and a roomy well secured toe box should definitely consider the Impulse as a fast every day trainer and racer.
All Altra's have a zero drop from heel to toe, when most conventional run shoes are 10mm and modern shoes 4-8mm.  As with all Altras  gradual transition to Zero Drop is important.   Particularly here with a 23mm heel stack, at the lower end of just about any shoe I run in, even racers, I have so far needed some Training (w) Heels to really make them sing for me by adding a bit more cushion and drop.  I added a soft 7mm heel wedge. Perfect!
What does the Impulse feel most similar to? The forefoot ride is quite similar to the Hoka Huaka or the Topo Magnifly but a bit more cushioned than the Magnifly and a bit more flexible and lively than the Huaka. The heel firmness even after the extra wedge is close to the Topo Magnifly or New Balance 1400 and firmer than say the Adios Boost or Boston and certainly Nike Lunar Tempo or Hoka Clifton 2.
Packed with innovation: FootShape, InnerFlex, StabiPods, the subtle varus wedge, and the asymmetrical lacing the Impulse has been on my feet daily for 2 weeks for its smooth stable ride, a rarity given how many shoes I run in and test. Impulse is a finalist for my Road Shoe of the Year.

Highly Recommended for:
Neutral or lightly pronating runners
Faster pace road running, up to marathon distances.

Overall Score: 4.85 out of 5
-0.1 for somewhat firm heel and a bit loose heel collar area, in particular at slow speeds when back on the heels
-0.05 for not including Training (w) Heel wedge for those transitioning to Zero Drop or those preferring a bit more heel.

Disclosure: The Altra Impulse was provided at no charge to RoadTrailRun. The opinions herein are entirely our own. RoadTrailRun is an affiliate of Altra Running and Running Warehouse and receives a small commission on sales through the links below to support our site.

Altra Impulse is available from Running Warehouse US women's here  men's here 
Altra Impulse is available from Running Warehouse Europe women's here  men's here 
Also  from Altra and other retailers at the display ads below.