Brooks Glycerin Flex Review
By David Salas
Brooks Glycerin FlexPrice: $170 at Running Warehouse
Weight: 9.1oz, 258g (men's size 9), 8.0oz, 226g (women's size 8)
Stack Height: 38 mm heel / 32 mm forefoot
Drop: 6 mm
Shoe Purpose: Daily Training, Flexible Midsole
Pros: Fills a void for those wanting a flexible shoe with higher stack height
Cons: Upper is not the most spacious, deep flex groove in the forefoot can cause some friction above it
RUNNING SHOE SUMMARY
The Brooks Glycerin Flex is a neutral daily training shoe that combines a significant amount of cushioning with a flexible sole. The goal of this is to provide a natural feeling foot strike with the ground. The Glycerin Flex uses the same DNA Tuned midsole as the Glycerin counterparts. At 9.1 ounces, the shoe offers some versatility with uptempo paces. The 38mm stack height also gives it sufficient cushioning for longer efforts. The flexible nature of this shoe makes for a very neutral offering, but does fill a void for those wanting something that is both flexible and highly cushioned.
SIMILAR SHOES: Skechers GO RUN (RIP)
PAST MODEL: new model
FIT
(To learn how a shoe should fit, check out our full podcast on fit by Matt Klein.)
David: The Brooks Glycerin Flex fits true to size in my men's 9.5. The flat knit upper is decently comfortable, but does feel a bit thicker than other knit uppers. With that said, it does hold its shaping well under load. There is a slight amount of stretch to it, but not enough to allow for foot translation. It runs a touch warmer because of the thickness. I did have a slight hot spot on the medial forefoot near a deep flex groove. I believe this was causing a little more friction in that area.
The fit is generally snug throughout. The volume is slightly low throughout the full length of the platform. The width is normal width to slightly narrow throughout the whole platform as well. The tongue is not gusseted, but did not have any issues with sliding. The padding of the tongue was also sufficient. I had no biting from the laces. The heel collar is slightly flexible with mild padding. It held its shaping well enough and I had no issues with rubbing.
The upper fits a touch snug and can run a touch warm. However, the general fit isn't bad and does well enough when running.
David's Typical Size: Men's US Size 9.5
Shoes that have fit David well: Nike Vomero 17, Saucony Ride 16, Puma Velocity Nitro 3
Shoes that have fit snug: HOKA Arahi 7
Shoes that have fit large: Salomon Aero Glide
Doctors of Running Checklist
Is This a Good Shoe for Walking: Average
Is This a Good Shoe for Standing: Average
Is the Forefoot Flexible: Yes
How Flexible is the Shoe: Very
Is This a Good Heel Bevel: Average
Recommended for Haglunds: No
Is This Shoe Orthotic Friendly: No
Recommended for Sockless: No
Durability Expectation: Average to Good
PERFORMANCE
David: The Brooks Glycerin Flex was an interesting experience. I have not run in a flexible shoe with this much stack height before. The only shoe that it reminds me of is the Skechers GO RUN line (RIP). The midsole has deep flex grooves that run the full length of the platform. These naturally form pods and a flexible design. The goal of this is to allow the runner to run with their natural path of movement.
The flexibility does come through in the ride. The heel is moderately beveled and does have a posterior-lateral bias. The deep flex grooves create a compression of the sole that flexes throughout the full length of your footstep. This makes for a very neutral experience.
Because I am used to high stack rockered shoes these days... I did find myself with some general calf soreness after running in these. The flexible design will make your ankle and knees move through a larger amount of range of motion. This isn't a bad thing, but something to note if you are not used to flexible soles.
The Brooks Glycerin Flex uses DNA Tuned as the midsole. This foam compound provides solid cushioning underfoot but runs on the firmer side. The firmness is appreciated in this model though. It helps keep a sense of structure in the platform when it is loaded. The DNA Tuned is best for daily training or long runs. The flexibility does provide some versatility for picking up the pace though.
The Brooks Glycerin Flex is a decent shoe, but not a shoe that will work for everyone. The runner must be comfortable with flexibility and have very neutral mechanics. The shoe isn't necessarily unstable, but your muscles will be working a bit more in this shoe than others that are out there.
STABILITY
(Learn more about stability in our full guide)
David: The Brooks Glycerin Flex is a very neutral shoe. The flex grooves are very deep and run the full-length of the shoe. The pods create a lot of give to the platform. This does raise the stabilization requirements for your foot. There is some noticeable sole flaring on the medial side at both the heel and the forefoot. I could feel it when I was walking. I was nervous that this would push me into inversion when I was running, but it didn't. The Glycerin Flex did not come off as unstable or difficult to run, but is still very neutral shoe.
Thoughts as a DPT: How Flexibility Impacts Your Movement
By David Salas, PT, DPT, CSCS
Flexibility is interesting. In muscles, it is how pliable your muscles are to stretch. In shoes, it is how much the foam bends underneath when it is loaded. In today's market, flexibility is something you are seeing less and less of. This is mostly in part due to stack heights climbing. When the stack height goes up, more modes of stability are needed to keep the platform moving fluidly. When you are higher off of the ground, you start to lose your sense of positioning, or proprioception, around your foot and ankle. If the platform is too narrow, you feel like you are on stilts and will have trouble balancing. This is one reason why you are seeing the platforms of shoes also gain width underfoot. The decrease in proprioception also causes you to stiffen up your muscles more around your joints. This is what people in the field refer to as joint stiffness.
Things change when you are running on a flexible platform. The stiffness that would come from a high stack rockered shoe decreases considerably. As the shoe flexes, you will also notice that your joints will move through larger ranges of motion. This will result in more ankle dorsiflexion, knee flexion, and global toe extension. The sensation may feel more "natural," but you will also be doing a little more work. This is especially noticeable in the calves.
There is no optimal amount of stiffness or flexibility. That is very dependent on the individual running. Some people will respond really well to stiff platforms, while others will do better with flexible platforms. Stiffer platforms usually respond with less range of motion and more joint stiffness, while flexible platforms result in larger ranges of motion and more freedom of movement.
RECOMMENDATIONS
David: I don't dislike the shoe, its just not for me. The main recommendation I would make for the Glycerin Flex is cleaning up the upper integration. The lower volume and thicker knit material make for a warmer environment. On a shoe this flexible, that can create a hot spot. For me it was the medial forefoot by the deep flex groove. Thankfully I never got any blisters, but it was an area worth noting.
WHO IS THIS SHOE FOR?
David: The Brooks Glycerin Flex is a neutral training shoe for those looking to have a high stack shoe with flexibility in the sole. The shoe does have a lot of give to it and runs relatively natural throughout the gait cycle. There are larger stability requirements that come with this type of shoe design, and so the runner must be okay with that. A flexible design like this also places a larger demand on your muscles. Your joints will be moving through larger ranges of motion due to the increased flexibility. If you have neutral mechanics and you are craving a more flexible offering, it is here.
GRADES
David
Fit: B (I would like to see some more volume. I would also like better integration with the sole on the medial side in the forefoot.)
Performance: B+ (The Glycerin Flex accomplishes a flexible ride with a higher stack height decent. Better for training miles.)
Stability: C (Very neutral design. Sole flaring medially is present, but nothing else that majorly contributes.)
Value: B- ($170 feels steep for this one. However, If you like DNA Tuned and want something flexible you can get good value.)
Personal: B (The hot spot in the medial forefoot does it for me. This is also a bit too flexible across the whole platform for me to be a go to daily trainer in my rotation.)
Overall Design: B
SHOP | SUPPORT DORBrooks Glycerin FlexPrice: $169.95 at Running Warehouse
Shop Men | Shop Women
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FURTHER READING
Find all Shoe Reviews at Doctors of Running here.
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