ASICS Barefoot Shoe Review: Piranha Sp4

If you’re in the hunt for a barefoot running shoe by ASICS, the Piranha Sp4 is perfect at what it does in functionally complimenting the human foot and preventing pavement pounding when you run by allowing the foot to land in its natural motion, a forefoot strike.
ASICS Barefoot Shoe Review: Piranha Sp4

The Piranha Sp4 is ASICS only barefoot shoe functionally specialized to strengthen the foot, especially the small muscles and bones in the foot, so you can withstand longer miles better.

Another strong positive effect of the Sp4 is the low-to-ground ride instantly corrects stride imbalances by making it easier for you to sense the ground so you can connect properly on your forefoot when you run.

Even more encouraging, one study demonstrated just how powerful minimalist running shoes, like the Sp4, are in prompting functional improvements in stride mechanics that’ll soften up your foot strike while improving the energy-saving elastic properties of the feet as compared with conventional running shoes.

The overwhelming benefits of minimal running shoes (which are thin, flat, wide shoes that feel like you are barefoot) are becoming more clear. For one, running in minimalist shoes is the best way to get your foot to work more efficiently. One study in the journal Medicine & Science in Sports & Exercise discovered that minimalist running shoes lowered muscle energy costs by enabling extra elastic energy storage in the Achilles tendon and the arch.

In keeping with this, another energy-saving attribute of minimalist running shoes was discovered whereby the light, barely-there feel of a minimalist shoe lightens the load on the leg by reducing the cost of transport on the leg.

One example of this came from a study in the Journal of Sport Science revealed that minimalist running shoes improved performance over a 5 km distance because of the lightness factor and by engaging a more effective forefoot strike, which is also directly related to reduced stress on the body.

  • The researchers compared the effects of minimalist running shoes (Asics Piranha SP4 — 5mm heel drop–shown below) vs the conventional running shoe on running performance during a timed trial in trained distance runners who were unfamiliar with wearing minimalist footwear, and who were heel strikers.
Asics Barefoot Shoe Review: Piranha Sp4
The minimalist shoe used in the study, the Asics Piranha SP4

ASICS Barefoot Shoe Review: Piranha Sp4

The researchers measured running economy via oxygen uptake. The researchers also examined foot strike as an economical factor as well as perceived comfort.

The researchers found that the minimalist running shoes resulted in a 22-second time trial performance improvement because of the shoes lightness AND because the runners reported feeling more comfortable in minimalist footwear.

Interestingly though, one participant stood out from the rest of the minimalist shoe-testers:

  • The participant who used the least amount of oxygen was the only one in the minimalist running shoe condition who landed with a forefoot strike whereas the others maintained a heel strike. However, the minimalist shoe testers had a reduced stride length and increased step rate, especially at faster running speeds of 13 -15 km/hr, but only trivial decreases in stride length and step rate at speeds slower than 13 km/hr.

The most important takeaway is that this finding illuminates the same basic conclusions in similar research showing that minimalist running shoes lead to immediate improvements in stride length which keeps your mechanics in neutral line by pulling the foot in more close to your center of mass (upper body) at landing. This effectively breaks the flow of high brake impact, which also enhances comfort because you are rolling more smoothly with the ground.

Lastly, the researchers concluded that a runner can certainly expect at least a 2% boost in run performance in minimalist footwear, even without prior experience to this shoe type.

The Take Home Message

Correcting mechanical imbalances can be simplified with minimalist running shoes because they make it easy for your foot to connect properly with the ground, essentially helping you undo years of straining movement patters while doing much more to functionally strengthen your feet than conventional running shoes could ever do!


Fuller et al. Effects of a minimalist shoe on running economy and 5-km running performance. J Sport Sci, 2016; 34(18):1740-1745.

Perl, D. P., Daoud, A. I., & Lieberman, D. E. (2012). Effects of footwear and strike type on running economy. Medicine & Science in Sports & Exercise, 44, 1335 – 1343. doi:10.1249/MSS.0b013e318247989e

Bretta Riches

"I believe the forefoot strike is the engine of endurance running..."

BSc Neurobiology; MSc Biomechanics candidate, ultra minimalist runner & founder of RunForefoot. I was a heel striker, always injured. I was inspired by the great Tirunesh Dibaba to try forefoot running. Now, I'm injury free. This is why I launched Run Forefoot, to advocate the health & performance benefits of forefoot running and to raise awareness on the dangers of heel striking, because the world needs to know.
Bretta Riches

P.S. Don't forget to check out the Run Forefoot Facebook Page, it's a terrific place to ask questions about forefoot running, barefoot running and injury. I'm always happy to help!