Brooks Glycerin GTS 21 Review (2024)

Brooks Glycerin GTS 21 Review: Premium GuideRails
By Matthew Klein

Brooks knows how to be consistent. For better or worse, they have been working with a similar set up for many years. While there have been big changes, including the integration of guiderails for stability, most changes have been small and careful. The foam has carefully gotten softer (but not super), many of the geometries used in the training footwear are similar and weights have remained fairly similar. The Brooks Glycerin GTS 21 is a great example of this. Featuring small tweaks that make it a better shoe than last year, including a better heel transition, a slightly wider fit, and a slightly softer sole, those new to the series should be able to transition in easily while prior users of the GTS 20 should be able to easily transition over. 

Brooks Glycerin GTS 21

Price: $159.95 at Running Warehouse
Weight: 10.7 oz, 303 g (men's size 9), 9.1 oz, g  (women's size 8)
Stack Height: 38 mm / 28 mm
Drop: 10 mm
Shoe Purpose: Premium Cushioned Moderate Stability Shoe

Pros: Well-cushioned, stable rearfoot/midfoot, good forefoot transition, slightly wider fit, better rearfoot transition
Cons: Sliding requires lace lock, heavier than last version, a bit too stiff in the rearfoot

RUNNING SHOE SUMMARY

The Brooks Glycerin GTS 21 is a premium cushioned stability daily training for those who want a smooth ride and traditionally cushioned shoe. A better beveled heel makes for smoother rearfoot geometry from the past version, adding to a well-transitioning ride that offsets the slight weight increase. The GuideRails continue to be used, making for a stiff but stable rearfoot and stable midfoot for those that need that. A new wider upper sits on top for those who need a little more room. Overall, the Glycerin GTS sees some small refinements that make for a better shoe than prior versions while still retaining consistent features Brooks is known for.

SIMILAR SHOES: ASICS Kayano 30, Mizuno Horizon 7
PAST MODEL: Brooks Glycerin GTS 20

FIT
(To learn how a shoe should fit, check out our full podcast on fit by Matt Klein.)

The Brooks Glycerin GTS 21 fits me true to size in my normal men's US size 10. The fit is slightly wide throughout the length of the shoe. This is offset slightly by a tapered toe box. The engineered warp knit upper sits slightly low against the top of the foot in the forefoot. The forefoot width is wide to slightly wide. This transitions into a slightly wide midfoot with an ungusseted moderately thick tongue. I had to really tie down the laces and eventually lace lock the shoe to get a secure fit. Before lace-locking the shoe, my foot would slide forward and which made the shoe feel slightly short. Lace-locking this shoe fixed this for me. The heel fits slightly wide to normal thanks to a ton of heel collar padding.

The heel counter is large and extremely stiff. Despite the padding, those with heel sensitivities will not do well in this shoe while those wanting a stiff heel counter will do great. The heel security is good thanks to the heel collar padding, but as mentioned additional tightening/lace locking may be needed to stop sliding if you do not have a wider foot. The inner liner of the upper is extremely comfortable and I have done several miles sockless in these. Those with experience running sockless will enjoy these while those without should still ease into this if you are interested. 

Typical Size: Men's US Size 10
Shoes that have fit Matt well: Saucony Guide 17, ASICS Kayano 30, Hoka Gaviota 5, Saucony Endorphin Elite, Nike Ultrafly
Shoes that have fit snug: Hoka Arahi 7, Saucony Kinvara 14
Shoes that have fit large: Salomon S/Lab Phantasm 2, Altra Timp 5

Doctors of Running Checklist

Is This a Good Shoe for Walking: Yes
Is This a Good Shoe for Standing: Yes
Is the Forefoot Flexible: Yes
How Flexible is the Shoe: Only in the Forefoot, Stiff Elsewhere
Is This a Good Heel Bevel: Moderately
Recommended for Haglunds: No
Recommended for Sockless: Yes
Durability Expectation: Above Average

PERFORMANCE

The Brooks Glycerin GTS 21 is a highly cushioned shoe for easy, recovery and long runs. The midsole features full-length DNA Loft v3, which is a nitrogen injected EVA foam. The foam is mild to moderately soft. Thanks to the GuideRails, the heel feels slightly firmer. There is a well-rounded heel with a decent bevel and crash pad that compresses well, making for a solid heel transition (that is light-years better than prior versions). This transitions into a slightly soft but stable midfoot. This then goes into a well-rockered, softer, mild to moderately flexible forefoot. The 10mm drop is noticeable for those who want a higher drop (although it feels less clunky than the 12mm drop of the Ghost series). The weight has increased slightly from the prior version and is now at the slightly heavier end of things.

Although this shoe is not responsive for faster efforts, it does feel slightly slighter than its listed 10.7 oz weight (men's size 9). It still does best for easier efforts, but the geometry does make it transition well and offsets some of that weight. The traction is good and easily tolerates road and mild smooth trail. I have gotten the ability to test this shoe in rain and wet road, something previous Brooks shoes have actually struggled with. These did great and have good road traction even on wet surfaces. The durability is actually quite good. I have 30 miles on my pair and there is only a tiny bit of abrasion on the outsole, so I expect an above-average number of miles out of the Brooks Glycerin GTS 21 compared to other shoes. 

STABILITY
(Visit our Guide to Stability to learn more about stability needs for runners)

The Brooks Glycerin GTS 21 is a moderate stability shoe. The majority of the stability is centralized to the heel and midfoot. There are guiderails on both the medial aspect of the midfoot and heel on the lateral aspect of the heel. These are combined with what feels like some kind of stiffening agent in this area. In addition to the sidewalls in the midfoot, this stiffness makes the rearfoot fairly rigid, offset somewhat by the decent bevel. Although not confirmed, it does feel like there is a long medial post from the heel to the midfoot. This makes for a highly stable heel and midfoot. This is not obtrusive into the arch but certainly creates a stiffer ride in the rearfoot and midfoot. The forefoot does not have any major stability measures outside of small sidewalls on each. I have not really noticed these, but the well-rockered forefoot and easy transition make forward motion easy. Those wanting midfoot and heel stability/stiffness and a more neutral forefoot will do best in this shoe. 

Thoughts as a DPT: How Much Stability You Actually Need 
By Matthew Klein

A frequent question we have received is asking how much stability each person needs. The easy answer is that it depends and what is most comfortable is more likely to work for that individual. The more complicated answer is explained best by knowing the amount of stability you may need can vary/change. Many people may not need stability and will do fine in neutral or even stable-neutral shoes. Those who do typically need some help controlling motion. We know that stability shoes do NOT necessarily change the amount of motion you go through into either pronation (rolling in) or supination (rolling out). They make a large impact on the rate or speed of these movements. Some people will see still movement quantity differences, but these tend to impact more the quality. It is imperative to understand that these motions, pronation and supination, describe movements and not pathologies. 

Pronation is a combined movement of ankle/foot eversion, dorsiflexion and abduction. Supination is a combined movement of ankle/foot inversion, plantarflexion, and abduction. It is normal during the initial contact/loading response (landing phase) into the midstance phases of gait for pronation to occur. It functions as a natural way to absorb shock during the first half of the foot being on the ground. Supination naturally occurs during the second half of the "stance phase" (foot on the ground) where the foot comes out of pronation, stiffens up (supinated positions naturally lock the joints of the foot/ankle) for the foot to effectively push off of during the terminal or propulsive phase of running gait. These motions have an optimal amount that is different for each person depending on many factors, but should be effectively controlled by muscles in order to adequately absorb shock and function. Some of the greatest tensile stresses to muscles/tendons occur during fast eccentric motions. The less control of a motion you have, the faster it tends to occur. 

How much stability need depends on how much help you need controlling motion. If you need help (some people do not and react poorly to stability), you will want enough stability to help you and not so much that it gets in the way of you shock absorbing. If you have too little stability, you may fatigue over longer mileage. If you have too much stability, you may not be able to shock absorb appropriately and may start getting some impact-related irritations. There is definitely such a thing as too much stability and more is not necessarily better. On the opposite end of the spectrum, too little stability can also be an issue for certain people. So while you will have a range of what you can tolerate, there may be some upper and lower limits as well. This range means you can use different amounts. Some people may need mild to moderate stability for recovery or long runs, but may be able to use a neutral or stability neutral shoe for shorter and faster efforts. Others may used high stability shoes recovery/long/normal runs and mild/moderate stability shoes for shorter faster runs. So if you need stability, don't feel stuck to one level (stable neutral, mild stability, moderate, motion control). We know training in a variety of shoes tends to decrease injury risk, so if you can afford it, it is okay to have a variety of stability shoes as well (Malisoux et al., 2015). 

References:

Malisoux, L., Ramesh, J., Mann, R., Seil, R., Urhausen, A., & Theisen, D. (2015). Can parallel use of different running shoes decrease running‐related injury risk?. Scandinavian journal of medicine & science in sports, 25(1), 110-115.

RECOMMENDATIONS

Brooks does consistency well with minor improvements. The improvements in the heel bevel and transition, the slightly softer sole and wider fit are great adjustments that will keep new and old wearers. My suggestion is not unique or special among review sites, but for $160 I highly encourage Brooks to start evolving from their current foam. For all the marketing that I have seen, this shoe is not that soft compared to others on the market. The non-GTS version does run softer, likely due to the lack of guiderails and what I suspect to be either a central post or stiffening agent (not confirmed). If they are going to advertise plushness, they need to upgrade this foam. My other suggestion is to reduce the weight. While this shoe runs far lighter than the listed weight, an almost ounce difference between the Glycerin and Glycerin GTS is quite surprising. This weight is in line with the Kayano 30, but I think Brooks can do better. To differentiate itself from the competition, a new foam that decreases weight while maintaining or improving the soft bouncy ride that is promised but isn't quite there would be appropriate. 

WHO IS THIS SHOE FOR?

The Brooks Glycerin GTS 21 is for those with slightly wider feet (there is a wide version of this shoe) who want a slightly more traditional stability shoe with a mild to moderately soft ride. The 10mm drop, stiffer heel and stable midfoot is classic for Brooks, along with a more traditional but consistent foam. The fit is wider for those who want it, while others may need to lace lock the shoe. The cost remains consistent from prior versions, which is great given the improved transition (heel) that drastically improves the ride compared to prior years. This shoe is an excellent alternative to the Brooks Adrenaline series as a softer version that is a little smoother for those who want a little more premium in their shoe. It competes well with the ASICS Kayano 30 as a more traditional alternative to the drastic changes seen in the Kayano series. In the wild, I have seen the Glycerin and Glycerin GTS used most frequently as a walking shoe. While the foam is a little firmer than I would expect for a company that advertises it so heavily as "floating", it does a great job providing a cushioned ride for all-day walking and wear. This gives it versatility on the market for those just wanting a walking shoe and is definitely something I would consider for those on their feet for long hours during the day. 

GRADES

Matt
Fit: B+/A- (Slightly wider fit, particularly in midfoot. Mild sliding that requires heel lock for those with normal width feet)
Performance: B+ (Better heel transition and smooth forefoot make for a great ride for easier and longer efforts)
Stability: A- [Moderate/High Stability] (Guiderails make for stiff heel and stable midfoot with neutral forefoot
Value: B (Maintains price from prior version, which is good given foams are older and not new age. Still a good shoe)
Personal: B (A good shoe but too stiff in the heel for me. I actually prefer the Glycerin non-GTS due to far lighter weight and less stiff heel )
Overall Design: B+

SHOP | SUPPORT DOR

Brooks Glycerin GTS 21
Price: $159.95 at Running Warehouse

Shop Men | Shop Women

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Editor's Note: As always, the views presented on this website belong to myself or the selected few who contribute to these posts. This website should not and does not serve as a replacement for seeking medical care. If you are currently injured or concerned about an injury, please see your local running physical therapist. If you are in the Los Angeles, Santa Barbara, Danbury and Stevens Point areas, we am currently taking clients for running evaluations. No content at Doctors of Running is written by AI.

***Disclaimer: These shoes were provided free of charge in exchange for a review.  We thank the people at Brooks Running for sending us a pair.  This in no way affected the honesty of this review. We systematically put each type of shoe through certain runs prior to review. For trainers and performance trainers, we take them on daily runs, workouts, recovery runs and a long run prior to review (often accumulating anywhere from 20-50 miles in the process). For racing flats we ensure that we have completed intervals, a tempo or steady state run as well as a warm-up and cool down in each pair prior to review. This systematic process is to ensure that we have experience with each shoe in a large variety of conditions to provide expansive and thorough reviews for the public and for companies. Our views are based on our extensive history in the footwear industry and years testing and developing footwear. If you are a footwear rep looking for footwear reviews or consultations on development, we are currently looking to partner with companies to assist, discuss and promote footwear models. Partnership will not affect the honesty of our reviews.

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