Karhu Flow4 Trainer Fulcrum General Info

The Karhu brand has a long history going back nearly 100 years. The key to the Karhu shoes is the “Fulcrum Technology” which has been around for about forty-five years and is designed to increase the efficiency of the foot strike by aligning the body and striving for “Efficient Forward Momentum”.

The Flow4 Trainer which was last updated two years ago in 2013 was perfect for those days where I needed short, fast training sessions.

The shoe is intended to be a lightweight, quick neutral trainer and it performed well while delivering a smooth and comfortable transition.

The Flow4 Trainer is the second Karhu I have run in and the shoe felt very lightweight and fast the moment I went for the first run.

I have also run in the Karhu Fast5 Fulcrum which is more of cushioned daily trainer which includes Karhu’s new full-length fulcrum.

The Flow4 Trainer is a shoe meant for shorter distances and weights around 8.6 oz. The shoe offers only a small touch of support as anticipated from a lightweight performance trainer.

Karhu Flow4 Trainer Fulcrum Sole Info

The Flow4 Trainer sole unit remains lightweight while incorporating the “Fulcrum Technology” to provide for more efficient running. The Karhu shoes are known for the built-in Fulcrum which is an EVA molded wedge.

The Flow4 Trainer’s has a heel-to-midfoot fulcrum versus other models which are starting to incorporate a full-length fulcrum, heel-to-forefoot.

Those models which now include a full-length fulcrum include the Karhu Fast5, Strong5 and Fluid3. Both fulcrum styles are designed to align the runner’s foot to increase efficiency.

The Fulcrum sits on top the sole unit as a separate piece that promotes midfoot striking as well as aligning the foot and providing more efficient forward motion during ground contact.

Due to Karhu and the “Fulcrum Technology” still be relatively new to many runners and integral to their brand, several diagrams have been included to assist in showing how the Fulcrum Technology works.

The Fulcrum provides a more efficient running stride as shown below in the “Benefits of Efficiency” diagram.

Diagram via Karhu.com showing Karhu Fulcrum Technology Efficiency

The sole unit continues using the same materials as its predecessor. The outsole is compression rubber, the midsole is an injected-molded EVA material while the forefoot area is blown rubber compound.

The compounds used in the sole allow for a very lightweight feel while delivering good grip and traction on the pavement or asphalt. As with any daily trainer that is used for short, fast-paced runs, the only concern would be durability on longer runs.

The minimal cushioning remained the same as the Flow3 Trainer which is anticipated for the intended daily use of the Flow4 Trainer. I felt that during each run there was smooth ground contact to compliment a quick, smooth transition through the entire foot strike.

The diagram below shows “how” the Fulcrum increases a runner’s efficiency depending on whether a runner is a heel, midfoot or forefoot striker.

The Fulcrum wedge works with each runner’s individual foot strike to promote forward movement.

Diagram via Karhu.com showing Karhu Fulcrum Technology for each Foot strike

During my runs, the overall comfort and time to get use to the Fulcrum was quick and something that felt natural.

The simple, lightweight nature of the midsole and outsole combined with the benefits of the Fulcrum design allow for a shoe which is resilient in handling quick training runs with ease.

Karhu Flow4 Trainer Fulcrum Upper Info

The Flow4 Trainer comes with very simple upper design which was updated in this version.

The upper is made of lightweight synthetic overlays under a thin mesh material which wrap the entire foot providing a comfortable feeling from the first run.

The previous version contained stitching found throughout entire upper while this latest shoe is nearly seamless.

The only stitching I found was in two places which had no impact on the comfort or feel of the shoe once laced up.

The first was minimal stiches on the medial side securing the Karhu “M” logo which could be used for a touch of stability.

The second place I noticed stitching was securing a small, narrow piece of fabric from the top of the toe to the laces in the middle of the toe box.

I am still curious as to why this material was there as it didn’t seem to have any structural or stability benefits during runs so not sure if it is needed.

The shoe liner provides a soft, comfortable sock-like feel. The heel cup includes two “pads”, one on each side, which are built into the liner to keep the heel securely locked in place for additional stability.

I did notice these during the first few runs but my they adapted to my foot. The heel pads remind me of the lightweight road and trail Montrail FluidFlex hybrid shoes which contained similar material for support.

There is a small, clear thing plastic band which is molded from one side of the heel cup to the other and I assume this is to provide a bit of stability in heel area.

The upper remains simple, very lightweight while providing a comfortable fit. This is achieved through its “seamless” design and using synthetic overlays and mesh to wrap the foot to allow for solid fit.

Karhu Flow4 Trainer Fulcrum Conclusions

The Karhu Flow4 Trainer Fulcrum is great for those runners who are looking for a solid lightweight shoe built for short, quick training and racing. This is not a shoe that is designed to be a high mileage trainer.

The Karhu Fulcrum Technology, which is the cornerstone of Karhu’s running shoe lineup, is based on increasing a runner’s efficiency during each foot strike.

Karhu kept the design simple by retaining the heel-to midfoot Fulcrum to assist with improving a runner’s foot strike combined with the lightweight, breathable seamless upper.

The final result is a comfortable and quick transition throughout the entire ground contact.

There is limited stability in this shoe as it’s targeted towards those neutral runners looking for a lightweight, fast trainer and racer.

For those runners who are looking for a shoe that is perfect for quick, fast training sessions, the Karhu Flow4 Trainer is a shoe to consider.

We thank the nice people at Karhu for sending us a pair of Flow4 Trainer Fulcrum to test. This did not influence the outcome of the review, written after running more than 50 miles in them.