Our verdict

We discovered that the Merrell Agility Peak 4 delivers a mixed bag of features, with notable strengths countered by significant drawbacks. We appreciated its stability and traction in challenging conditions, yet couldn't overlook the firm, muted ride of the FloatPro midsole. It doubled effectively as a hiking shoe, but durability concerns arose from the outsole and upper. Through rigorous lab analysis and real-world testing, we uncovered a range of strengths and weaknesses, leaving us questioning its overall performance.

Pros

  • Really stable ride
  • Excellent for winter weather
  • Thrives in muddy conditions
  • Lugs excel uphill and downhill
  • Doubles as hiking shoe
  • Ample stack height for heel strikers
  • Upper fits most types of feet

Cons

  • Lacklustre durability
  • Average-at-best breathability
  • Actual drop differs from 6 mm

Audience verdict

84
Good!

Who should buy

We highly recommend the Merrell Agility Peak 4 for:

  • Trail enthusiasts seeking a stable and responsive ride without the bulk of traditional trail shoes.
  • Heel strikers who appreciate the support of a firm midsole during their trail runs.
  • Adventurers who need a versatile shoe for both trail running and hiking that features a Vibram outsole.

Merrell Agility Peak 4

Who should NOT buy

We found the FloatPro foam in the Agility Peak 4 to be on the firm side, and the thick outsole doesn't help at all. This means if you're after a plush, soft feel underfoot, the Agility Peak 4 might not be a good pick. We think there are better choices out there, like the ASICS Trabuco Max 2, if you're seeking a comfortable, cloud-like ride.

In our lab tests, we also noticed that the shoe lacks durability, particularly in the toebox, heel, and outsole. Fortunately, the newer version, the Merrell Agility Peak 5, seems to address many of the predecessor's issues. Based on our findings, we recommend considering the upgrade for a better experience.

Merrell Agility Peak 4

Breathability

Our first impression of the Agility Peak 4 was that the toebox seemed to lack airflow due to its dense structure and absence of ventilation holes. We decided to put it to the test with our smoke-pumping machine.

As expected, the results showed minimal airflow in the toebox area. Merrell did design the tongue to allow some heat and vapor to escape, which earned the shoe a 3/5 in our test.

When we assessed the shoe over the light, it confirmed the lack of ventilation through the engineered mesh. This doesn't necessarily mean it's a flaw—it just makes the shoe less suitable for hot summer runs but a solid choice for winter.

Merrell Agility Peak 4 microscope

To understand why the toebox doesn't allow air through, we headed to the microscope zone in the lab.

Merrell Agility Peak 4

There, we confirmed our suspicions: the material is indeed very dense with no holes at all.

The upper does have decent padding, though. We believe it could even handle ultras, but based on our tests, we'd suggest skipping summer events with this shoe.

Test results
Agility Peak 4 3
Average 3.3
Compared to 76 trail running shoes
Number of shoes
1
Breathability
5

Durability

Toebox durability

One common advantage of thick and dense uppers is better durability. That's why we were keen to test the Agility Peak 4.

However, the results didn't meet our expectations. Although a 3/5 is decent, we thought a really dense upper like this one would do slightly better. Plus, Merrell didn't add significant protective pieces to the toebox—only some coverage on the toecap.

Merrell Agility Peak 4 Toebox durability
Test results
Agility Peak 4 3
Average 3.1
Compared to 56 trail running shoes
Number of shoes
1
Toebox durability
5

Heel padding durability

We took our Dremel to the heel padding area and were disappointed with a 2/5 score, a step down from before.

This is concerning for those who tend to wear the Achilles area of running shoes.

Merrell Agility Peak 4 Heel padding durability
Test results
Agility Peak 4 2
Average 2.9
Compared to 54 trail running shoes
Number of shoes
1
Heel padding durability
5

Outsole hardness

Hoping for better results with the outsole, we checked the hardness of the Vibram rubber.

Our durometer showed 88.4 HC, indicating it's quite hard and should presumably lead to positive results in our next test.

Merrell Agility Peak 4 Outsole hardness
Test results
Agility Peak 4 88.4 HC
Average 85.3 HC
We use an average of four tests. The photo shows one of those tests.
Compared to 99 trail running shoes
Number of shoes
72.5 HC
Outsole hardness
95.0 HC

Outsole durability

For our final Dremel test, we revved up the Dremel and crossed our fingers.

Sadly, the hard Vibram rubber also fell short, hinting that durability might be the Agility Peak 4's major flaw. We noticed a 1.8-mm indentation, which is just too deep.

Then it clicked for us. This isn't the highly praised Megagrip from Vibram, but the Eco-Step Evo—a rubber that doesn't perform as well.

Merrell Agility Peak 4 Outsole durability
Test results
Agility Peak 4 1.8 mm
Average 0.9 mm
Compared to 49 trail running shoes
Number of shoes
0.0 mm
Outsole wear
2.0 mm

Outsole thickness

At least Merrell equipped the AP4 with a thick, 3.0-mm rubber layer, which complements the lugs we'll discuss shortly in this same review.

Merrell Agility Peak 4 Outsole thickness
Test results
Agility Peak 4 3.0 mm
Average 2.4 mm
Compared to 99 trail running shoes
Number of shoes
0.9 mm
Outsole thickness
6.5 mm

Weight

The Merrell Agility Peak 4 isn't a small, thin shoe, yet it doesn't feel too heavy.

On our scale, it weighed in at 10 oz, which is about average for shoes with similar cushioning. We're pleased with this result!

Test results
Agility Peak 4 10.30 oz (292g)
Average 10.34 oz (293g)
Compared to 99 trail running shoes
Number of shoes
7.51 oz (213g)
Weight
13.37 oz (379g)

Cushioning

Heel stack

Let's measure the stack height to get a clear picture of what we're dealing with.

Merrell Agility Peak 4 heel

Our digital caliper showed 34.4 mm in the heel, indicating that this shoe can comfortably accommodate heel strikers.

Merrell Agility Peak 4 Heel stack
Test results
Agility Peak 4 34.4 mm
Average 32.2 mm
Compared to 99 trail running shoes
Number of shoes
16.1 mm
Heel stack
42.4 mm

Forefoot stack

We measured the forefoot too, finding a thickness of 25.1 mm. This measurement seems pretty standard, making this shoe a great all-rounder for various distances.

Merrell Agility Peak 4 Forefoot stack
Test results
Agility Peak 4 25.1 mm
Average 24.4 mm
Compared to 99 trail running shoes
Number of shoes
15.2 mm
Forefoot stack
33.9 mm

Drop

In the lab, we measured the drop—the difference between the heel and forefoot height—at 9.3 mm. This differs from the 6-mm offset claimed by the brand, making the shoe more suitable for heel strikers.

Merrell Agility Peak 4 Drop
Test results
Agility Peak 4 9.3 mm
Average 7.8 mm
Compared to 98 trail running shoes
Number of shoes
-0.1 mm
Drop
17.3 mm

Insole thickness

A simple way for brands to enhance underfoot comfort and create a cushioned feel is by adding a thicker-than-average insole to the shoe.

That's exactly what Merrell did, using a very thick 5.8-mm insole.

Merrell Agility Peak 4 Insole thickness
Test results
Agility Peak 4 5.8 mm
Average 4.7 mm
Compared to 99 trail running shoes
Number of shoes
2.7 mm
Insole thickness
9.8 mm

Midsole softness

Note: a low durometer measurement equals a soft material, whereas a high measurement means it's firm.

Despite the thick insole and a decently cushioned midsole, the ride feels firm. We noticed this during our test runs and confirmed it with using our Shore A Durometer on the FloatPro foam.

The result of 29.9 HA makes this trail shoe a good choice for those who prefer a stable, secure ride and don't mind sacrificing some plushness underfoot.

Merrell Agility Peak 4 Midsole softness
Test results
Agility Peak 4 29.9 HA
Average 23.2 HA
We use an average of four tests. The photo shows one of those tests.
Compared to 75 trail running shoes
Number of shoes
9.4 HA
Midsole softness (soft to firm)
39.0 HA

Difference in midsole softness in cold

With an upper that's less breathable, this shoe shines for winter hikes and runs. It gets even better—our tests showed that the FloatPro foam only gets 23% firmer in cold temperatures, which is a great result.

Merrell Agility Peak 4 Difference in midsole softness in cold
Test results
Agility Peak 4 23%
Average 26.7%
Compared to 75 trail running shoes
Number of shoes
0%
Difference in midsole softness in cold
100%

Stability

We previously discovered the Agility Peak 4 to be super rigid in our manual assessment, which made us eager to test it with our force gauge. Finding the same rigidity from a longitudinal perspective wouldn't be ideal for those looking to use this shoe for easy runs or hikes.

Luckily, it turned out to be much more flexible, probably thanks to the FlexConnect system in the midsole. We recorded a 29.7N result after bending the shoe to 90 degrees—a fairly average outcome.

Lateral stability test

Having a firm midsole naturally makes a shoe stable, but the Merrell Agility Peak 4 felt even more stable than its firmness alone would suggest—there must be something else, right?

Indeed, one of the key features is the midsole sidewalls, which guide the foot forward and prevent lateral collapse. But there's more to it.

Torsional rigidity

Another key factor in the shoe's stable ride, making it suitable even for runners with stability needs, is its impressive rigidity.

We really struggled to bend the shoe, earning it a 5/5 score—a rating usually reserved for carbon-plated shoes. The downside could be some discomfort on easy runs and technical terrain. So, if you're often facing sharp turns and descents, you might find the Hoka Zinal 2 a better fit.

Test results
Agility Peak 4 5
Average 3.5
Compared to 93 trail running shoes
Number of shoes
1
Torsional rigidity
5

Heel counter stiffness

The heel counter is also quite stiff, scoring a 4/5 in our assessment. This design is aimed at enhancing stability, though those with sensitivity to rigid heel counters might find it a bit too much.

Test results
Agility Peak 4 4
Average 3.2
Compared to 91 trail running shoes
Number of shoes
1
Heel counter stiffness
5

Midsole width in the forefoot

Our first measurement of the shoe's dimensions was in the widest part of the forefoot, which we recorded at 109.8 mm.

Merrell Agility Peak 4

It's not very wide, but now everything makes sense—to achieve a stable ride in a moderately narrow shoe, other features must be implemented, as we demonstrated earlier with the torsional rigidity and the stiff heel counter.

Merrell Agility Peak 4 Midsole width in the forefoot
Test results
Agility Peak 4 109.8 mm
Average 111.9 mm
Compared to 99 trail running shoes
Number of shoes
102.1 mm
Midsole width in the forefoot
126.0 mm

Midsole width in the heel

The heel is comparatively wider, measuring 91.0 mm. This makes sense since the shoe's design favors heel strikers based on its geometry.

Merrell Agility Peak 4 Midsole width in the heel
Test results
Agility Peak 4 91.0 mm
Average 89.6 mm
Compared to 99 trail running shoes
Number of shoes
77.2 mm
Midsole width in the heel
109.3 mm

Flexibility

Stiffness

We previously discovered the Agility Peak 4 to be super rigid in our manual assessment, which made us eager to test it with our force gauge. Finding the same rigidity from a longitudinal perspective wouldn't be ideal for those looking to use this shoe for easy runs or hikes.

Luckily, it turned out to be much more flexible, probably thanks to the FlexConnect system in the midsole. We recorded a 29.7N result after bending the shoe to 90 degrees—a fairly average outcome.

Test results
Agility Peak 4 29.7N
Average 28.6N
We use an average of four tests. The video shows one of those tests.
Compared to 99 trail running shoes
Number of shoes
10.5N
Stiffness
54.5N

Difference in stiffness in cold

We repeated the 20-minute freezer test with the stiffness measurement, and the AP4 was 24.2% firmer this time. It's not a significant difference, and we believe most runners probably won't even notice.

Test results
Agility Peak 4 24.2%
Average 35.7%
Compared to 96 trail running shoes
Number of shoes
0%
Difference in stiffness in cold
102%

Grip / Traction

Lug depth

Back to the outsole, we found 4.4-mm chevron-shaped lugs designed to improve traction in muddy or wet conditions.

Merrell Agility Peak 4 lugs

This lug length seems adequate to us since it can handle most terrains. However, combined with the 3.0-mm base, it results in a very muted ride that feels really bad in roads, with a total height of 7.4 mm for the entire Vibram outsole. Stick to the trails, please.

Merrell Agility Peak 4 Lug depth
Test results
Agility Peak 4 4.4 mm
Average 3.5 mm
Compared to 99 trail running shoes
Number of shoes
1.7 mm
Lug depth
5.8 mm

Size and fit

Toebox width at the widest part

The upper has an average fit that didn't feel roomy or snug to us—it was just okay. We measured 97.6 mm in the widest part of the toebox, which confirms our impressions.

Merrell Agility Peak 4 Toebox width at the widest part
Test results
Agility Peak 4 97.6 mm
Average 98.7 mm
Compared to 99 trail running shoes
Number of shoes
92.0 mm
Toebox width at the widest part
104.9 mm

Toebox width at the big toe

However, with 80.1 mm in the big toe area, we're happy to confirm there's a bit more room for your toes to wiggle!

Merrell Agility Peak 4 Toebox width at the big toe
Test results
Agility Peak 4 80.1 mm
Average 78.9 mm
Compared to 61 trail running shoes
Number of shoes
70.5 mm
Toebox width at the big toe
92.1 mm

Tongue: gusset type

The tongue is securely attached to the sides in a bootie style, effectively blocking any rocks or debris from sneaking into the shoe.

This is exactly the kind of feature we love to see in a proper trail running shoe!

Merrell Agility Peak 4 Tongue: gusset type
Test results
Agility Peak 4 Bootie

Comfort

Tongue padding

The tongue has decent padding, but don't expect it to feel like a pillow between your foot and the instep.

Merrell Agility Peak 4 tongue

We measured it at 4.3 mm, which is quite a bit less than the average shoe. However, the tongue incorporates some extra layers that add a bit of cushion.

Merrell Agility Peak 4 Tongue padding
Test results
Agility Peak 4 4.3 mm
Average 6.4 mm
Compared to 99 trail running shoes
Number of shoes
1.5 mm
Tongue padding
12.2 mm

Heel tab

We found a finger-loop, a horizontal pull tab on the heel, making it easier to slide our feet into the shoe.

Merrell Agility Peak 4 Heel tab
Test results
Agility Peak 4 Finger loop

Removable insole

The insole is removable because it isn't glued to the strobel board. It also has a super-big FloatPro logo, so you won't forget the firm-like-a-brick foam Merrell used in this shoe.

Merrell Agility Peak 4 Removable insole
Test results
Agility Peak 4 Yes

Misc

Reflective elements

The Merrell Agility Peak 4 lacks reflective details, so it's not the best choice for night trail runs.

Merrell Agility Peak 4 Reflective elements
Test results
Agility Peak 4 No