Adidas Adizero Boston 12 vs Saucony Endorphin Speed 4: Which Performance Trainer Fits Your Running

Introduction

The Adidas Adizero Boston 12 and Saucony Endorphin Speed 4 are two of the most asked-about performance trainers, and for good reason. Both are designed to do a little bit of everything: daily training miles, faster workout sessions, and even racing for some runners. They share a lot of DNA, but the differences in the heel and midfoot are significant enough that choosing between them comes down to your own preferences.

Specs at a Glance

The numbers are close. In a men’s size 9, the Boston 12 weighs 9.4 oz (267 g) with 37 mm of heel stack, 30.5 mm in the forefoot, and a 6.5 mm drop. The Endorphin Speed 4, also in men’s size 9, comes in at 8.2 oz (233 g) with 36 mm of heel stack, 28 mm in the forefoot, and an 8 mm drop. The Endorphin Speed 4 is roughly an ounce lighter, and that difference shows itself in the right situations.

Fit and Upper

Adidas footwear typically runs a bit narrower through the midfoot, and the Boston 12 follows that pattern. The heel and midfoot are very dialed in with a secure lockdown, while the forefoot is a little wider with more volume. The thin mesh upper is not soft or plush, but it is not uncomfortable either. It simply reflects the performance-focused nature of the Adizero lineup.

The Endorphin Speed 4 has a similarly accommodating forefoot with decent volume through the top, but the heel and midfoot width feel much more normal and forgiving compared to the Boston 12. Its upper material is a little softer and plusher, giving it a more trainer-like feel while still staying airy and performance-oriented. If you want that track-spike-tight midfoot and heel fit, the Boston 12 is the stronger choice.

Ride and Performance

Both shoes have wide footbeds and genuinely good traction. The Boston 12 uses Continental rubber, while the Endorphin Speed 4 relies on a lattice outsole design. Both grip the ground very well for the category.

Underfoot, the platforms are structured differently. The Boston 12 uses plastic energy rods as its stiffening agent, which allow some flex when you bend the shoe. Its midsole layers Lightstrike Pro mostly in the forefoot over Lightstrike in the heel, producing a firmer base in the heel and a soft, compliant, bouncy forefoot. The Endorphin Speed 4 uses a lighter PEBA-based midsole, PowerRun PB, across the entire platform with a nylon plate that also offers some flexibility, which helps explain its lower weight.

Both shoes have gradual but noticeable late-stage forefoot rockers that create a rolling sensation onto the forefoot while still delivering good pop.

The Big Difference: Heel and Midfoot

This is where the two shoes diverge. The Boston 12 features a large posterior lateral bevel that is almost intentionally undercut, pushing you into a fast transition from heel to midfoot. The firmer Lightstrike heel, combined with more rubber overall, creates a firm, quick-switching initial contact and a snappy pronation moment into a wide, leverable forefoot.

The Endorphin Speed 4 feels softer and more compliant in the heel thanks to PowerRun PB, and it keeps you feeling centered with a more balanced platform rather than biasing you forward. It can feel slightly clunky at first, but as the shoe breaks in or when you run faster, that sensation fades quickly thanks to the compliant PEBA midsole. Heel to toe, the Endorphin Speed 4 delivers a more consistent, balanced experience, while the Boston 12 rolls hard through the heel and again from late midfoot to forefoot.

Which One Should You Buy

If you want more rigidity in the heel, a streamlined fit, and a narrow, track-spike-like lockdown through the midfoot and heel, the Boston 12 delivers exactly that. If you prefer something more accommodating and plush, with a softer heel and a smoother, more balanced transition from heel to forefoot, the Endorphin Speed 4 is the better match.

Both are genuinely solid performance trainers. The Boston 12 earned an honorary year-end list spot, and the Endorphin Speed 4 is a strong candidate to do the same. Matching the shoe to your fit and ride preferences is what will make either one work for you.

Conclusion

These two performance trainers overlap in versatility, forefoot room, and traction, but they split clearly on character. The Boston 12 is firmer, faster-rolling, and more locked down through the back half of the shoe. The Endorphin Speed 4 is lighter, plusher, and more balanced across the full stride. Choose based on which of those two experiences fits your running.