Newton has carved its niche in the athletic shoe industry as the most prominent proponent of forefoot running. They’re a relatively young company – less than four years old – but they’ve built a fiercely loyal following, particularly within the triathlon community. The Sir Isaac is a successor to Newton’s popular Gravity road trainer, and is a road shoe with good crossover potential to the world of trail running.
About the Newton Sir Isaac
The Sir Isaac is a neutral guidance trainer built to accommodate a wide range of foot types. It combines Newton’s distinctive features for midfoot/forefoot runners with some design tweaks for improved traction and durability to go off the beaten path.
Sir Isaac Features
- Upper: Fast drying mesh with synthetic leather accents
- Lining: Energy-return sock liner
- Midsole: Single-density, high rebound EVA, with midfoot chassis shank for stability
- Outsole: High-wear carbon rubber with traction tread
- Weight: 10.9 oz
- MSRP: $149
Newton Sir Isaac Review
In a nutshell, the Sir Isaac is a slightly more rugged, more durable version of Newton’s preexisting models, featuring all the unique innovations for committed forefoot runners, along with a few noticeable changes to the outsole and the upper.
Sir Isaac outsole
Sir Isaac’s outsole is a high-durability carbon rubber with traction treading for increased grip on dirt or other loose surfaces. This material also covers the actuator lugs, which are the most prominent feature of all Newton running shoes. The outsole isn’t as knobby or sticky as offerings from dedicated trail running brands, but it’s adequate for basic off-road use.
Actuator lugs on outsole
Newton’s actuators extend almost a half-inch from the remainder of the outsole, and serve as the main impact zone for forefoot-striking runners. They compress into the midsole of the shoe upon impact, then act as a lever to propel you into your next stride (Newton calls this its Action/Reaction technology). It’s an energy-return design, and since each of the four actuators function independently, it allows all the joints and small muscles of the foot to flex and shift as they would if barefoot.
The midsole is also designed to promote forefoot running, with a rockered heel area, and Met-flex grooves for forefoot flexibility. However, if you’ve previously used Newton’s Gravity shoe, you’ll notice the forefoot flexibility in the Sir Isaac is significantly less. The forefoot area is nice and wide to allow for metatarsal spreading during the forefoot impact phase.
Closed mesh upper
Another trail-inspired modification is the closed mesh upper, which is very effective at keeping out debris and small rocks. The mesh retains good ventilation, however, and is quite comfortable overall. Newton shoes also feature slip-proof laces, made of 100% recycled content, which help dial in your preferred degree of snugness.
Good Sir Isaac
- Great debris resistance from closed mesh upper
- Improved traction from high-wear carbon rubber outsole
- Comfortably wide forefoot toebox
- Good overall durability across varied terrain
Bad Sir Isaac
- Traction slightly unsteady on technical footing
- High retail price
- Long adaptation period for longtime heel strikers, although Newton provides instructional brochures and videos for guidance
Bottom Line: Newton Sir Isaac Shoes
The Sir Isaac succeeds in translating all the innovations of Newton’s footwear to a road trainer with good off-road capability. If you already like Newtons and want a more durable, rugged version, rejoice! However, if you’re not comfortable with forefoot running or uninterested in transitioning your running style, this probably isn’t the shoe for you.
More Info: Visit NewtonRunning.com
Donald is an ultrarunner/triathlete in Monterey County, CA. He provides occasional reviews here on FeedTheHabit.com, and is the author of a website featuring gear reviews, photo tours, race reports, training diaries and life lessons, all of which can be found at 
So, Donald… tell me what you mean by “forefoot running?” I assume I could go to Newton’s site and learn more, but give me the quick run-down.
Jason – Basically, forefoot running means that you land on the front part of your foot instead of the heel area, like you would do if you were barefoot. It causes a whole chain reaction further up the body – more knee and hip flexion, more upright posture – and there’s some evidence that it decreases impact forces and injury risk for many runners. The trick is that unless you’re barefoot, you really have to focus on form the entire time, and most traditional running shoes with elevated heels make forefoot striking all but impossible. Newtons differ in that the main impact zone is in the forefoot, and the heel is purposely minimized and rounded to promote landing on the forefoot with each step.
The Newton website also has several videos to help visualize the differences in running form, and provide a much more thorough explanation of its benefits.
Interesting… I’ll check out their site. With my flat feet and aching knees at times it may be something to look at.
Here’s a great video from Netwon that I found super-informative:
So, Donald… how do you feel “forefoot running” works on the trails? It seems like you might have a bit less traction and stability on trails vs. on pavement.
These look interesting, after converting to barefoot running trainers like FiveFingers and Feelmax http://www.lovethoseshoes.com/Range.asp?RangeID=292&Voucher=barefoot like these ones, i will take something great to convert me back to a ‘cushioned’ trainer, but this looks good
Jason – Forefoot running works pretty well on the trails – in fact, I use the Sir Isaacs above exclusively for trail running. The form does get a little tricky on long, steep downhill stretches or on super-technical patches of trail, but for the most part the carryover is pretty effective. I haven’t found shoe stability to be an issue, but traction with the Sir Isaacs is indeed a notch below dedicated trail dogs like La Sportiva or Vasque. Newton recently announced a more rugged trail model for 2010, so it will be interesting to see the traction upgrades.
Donald- Strange question, what kind of socks are you wearing in the pic of your feet with the Sir Isaacs on? They look either light blue or gray. Oh by the way, I’m on my 3rd pair of Newtons and I love em. I like the Sir Isaac’s for lite trail running as well. I understand that sometime in June 2010 they will introduce a trail specific shoe. Thanks- Tim
Tim – Those are the trail version of Drymax socks, my absolute favorite for all kinds of running. I’ve worn them for all my ultras over the past year, and they’re amazing for moisture management and blister control.
You’re correct in noting that Newton has a dedicated trail model coming out next year – I can’t wait to try it!
Donald- Thanks!