Altra goes “back to the future” with the latest version of its moderately cushioned zero-drop high mileage trainer. The last returns to the shape of the 1.5 version, with the same moderately firm midsole responsiveness of early Altra models. Modernized updates to the upper make the shoe comfortable and breathable, and a new outsole configuration has more padding in the forefoot. 

Fit
The big development with the Altra Instinct 4.0 is the company’s revision back to the last shape found on the Instinct 1.5; it is slightly less curved than more recent versions of the Instinct, and accommodates a wider variety of users. Its toe box is still pleasantly wide for full toe splay, but the midsole and heel are snug enough that the shoes don’t feel sloppy. There is plenty of vertical clearance in the toe box also. Between the width and height of the toe box, runners with narrow feet might have some slippage with frequent turns or changes of direction. 

Comfort
Another welcome update to the Instinct 4.0 is a softening of the rigid toe bumper at the front of the shoe, which some users found irritating on previous models. The bumper is still there, but it is softer and more pliable for improved comfort. The new mesh design breathes and ventilates well, and moderate padding on the tongue and around the ankle collar provide a soft and comfortable ride on high mileage days.  

Responsiveness
Altra tinkered with the firmness of its EVA compound on the Instinct 4.0, looking to combine this with its proprietary A-bound energy return compound to achieve a moderately firm sweet spot. Our testers were not impressed with the overall energy return compared to other shoes in our testing; some of this may be attributable to the zero-drop platform which is much more effective for midfoot strikers. We also found minimal spring or bounce in the toe off phase of the gait cycle. 

Ride Quality
The Instinct 4.0 isn’t our best choice for a 5K, but we laced them up with confidence for easy 20-milers or everyday. This is another category that is heavily dependent on running form: heel strikers will experience poor transition of momentum from heel to toe, while midfoot strikers will roll forward much more efficiently. Longitudinal and horizontal grooves in the midsole and outsole allow natural foot movement in stance phase, which improves the feeling of smoothness for midfoot runners.

Speed
The Instinct 4.0 is definitely more of an everyday mileage shoe than a speed work weapon. This model also has one of the largest weight discrepancies between the listed spec weight and our standard size 11 test pairs, so the challenge of fast turnover is accentuated with larger foot sizes.