Karhu Fusion Ortix 2021 Review by NorthernRunner.com

When you look at the 100 plus years of Karhu’s history it strikes you that Karhu has always been a brand that is a step ahead. They were using Finish birch to give their spikes a bit of spring in 1916 and had ‘Air Cushion’ in their shoes in the 1970’s, before any other brand had started putting cushioning into their shoes. They noticed the drawback with cushioning in that it essentially makes you go ‘up and down’ through your cycle and not forwards. As a result, they developed the ‘Fulcrum’ in 1986 to add some clever forward propulsion. In recent years other brands have put rockers into their shoes to accomplish a similar thing but Karhu was first.

The launch of the new Karhu Fusion Ortix 2021 and HiVo (higher volume) version has generated some excitement at Northern Runner. The Fusion is a neutral everyday training shoe and has enough cushioning and durability for the longer runs. It is no surprise that the shoes have an initial feeling that they are built to last. The upper is a soft knitted mesh. There is a good level of padding in the heel cup and tongue giving a luxurious feel to the shoes. You know straight away that they’ll feel comfortable for a good length of time. When you are motivating yourself to get out the door for your first run of the day at 5.30 am and it’s dark and cold, the comfortable, cushioned, solid and secure feel of the Fusion Ortix 2021 makes it easier to get out the door and get moving!

The heel to forefoot drop is 8mm and the shoes are surprisingly flexible in the forefoot. This makes it usable for the heel strikers or the midfoot strikers. The toe box is much more rounded than the previous models. Not as broad and rounded as an Altra or Topo shoe but not the pointed toe box shape that tends to restrict foot function. The Fusion 2021 is available in HiVo (higher volume) for those that need a little more space to spread out. I found that the length was a little short compared to previous Karhu’s and just went for ½ size up. If you’re not sure on sizing then drop us an email at sales@northernrunner.com.

The cushioning in the latest Karhu Fusion is without doubt substantial. It isn’t too soft and squishy, with a firmer compression and a good rebound. It is a common misconception that soft feeling shoes absorb more shock. Softer shoes just compress more, which gives the illusion of shock absorption. Your foot doesn’t ‘know’ it has hit the floor, so you don’t activate your feet to cushion, stabilise and spring you forward. There is some compression in the midsole when your foot lands on the floor in the Karhu Fusion but, you don’t sink into the cushioning and lose momentum. This is because the initial soft feel is supplied by an Eva strobel board on top of the midsole. The midsole itself is more solid, which makes it more durable, but doesn’t give the ride a ‘hard’ feel. It’s a great combination.

The new more rounded toe box gives your foot the space to spread on impact and push you onto your next stride. Cushioned midsoles of this level maintain their rebound qualities longer. As you would expect, after two hour plus long runs in the Fusion 2021 the shoes feel as good as they did at the outset.

Midsoles of this quality are also more durable. I’m 200 miles in and my Fusion’s still run as if they were new. Of course they will eventually wear out and how many miles you get out of a pair of shoes depends on how light you are on your feet! My feeling is that for me these will last a lot longer than average.

In my first run in the Karhu Fusion the solid feel of the shoes made me feel like I was running slowly. Comfortably trotting a long rather than flying. I noticed that the Fulcrum stimulated my glutes and hamstrings to lift my leg straight up underneath me, rather than pull my leg backwards. This means that you run with a more upright posture. The classic postural mistake is to lean forward at the waist. This makes you feel like you are going faster but essentially arrests the falling forward required to run. You end up heavier on your feet and you land with your feet in front of your centre of gravity. We all tend to do this and particularly as we get tired. This is because modern life dictates that we spend a lot of time sitting down. We become weak around the middle and use our quads too much. The Fulcrum helps combat this postural error. The reality was that I wasn’t running slower. In fact when running downhill, which I do a lot as it’s very hilly in County Durham, it is noticeable that you don’t hit the ground as hard and your mile splits are quicker despite you feeling like you are comfortably trotting along.

The Fulcrum is a firm piece of midsole in the midfoot area of the shoes and shaped in such a way that it reduces the ‘up and down’ motion of running and gets you moving forward. Other brands have designed similar mechanisms. For example, the rocker that is in Hoka running shoes and the e-Ride that is in Scott running shoes. The difference is that both these mechanisms encourage you to pull your leg backwards. This does increase cadence and reduces over striding and makes you feel like you are flying along. The difference I found is that with the Fulcrum in Karhu footwear, the pull was ‘up’ where as with the shoes with rockers in the pull was ‘back’. I couldn’t actually feel the Fulcrum in the shoe. The only thing I was aware of was the flexibility in the forefoot of the shoe.

Karhu use a few different length Fulcrums in their running shoes. The Fulcrum in the Fusion 2 is the shortest and designed for neutral runners. The Fulcrum in the Ikoni is a slightly longer and offer some pronation support. The Karhu Ikoni is better suited to you if you pronate.

Initially I found that the slightly different running action that these shoes stimulated made my calves, hamstrings and glutes a bit stiff. As they weren’t used to lifting as much. My legs got used to this movement quickly. After a month of having the Karhu Fusion as one of the shoes I alternate with I have noticed that my cadence has increased and ground reaction time has reduced as measured on my Stryde foot pod. Essentially I am becoming lighter on my feet. I am now so used to running in a more upright position that when I am getting tired running in other footwear and start to bend at the waist I am aware of my fault and I can correct it.

All the points above make this a fantastic cushioned, comfortable road running shoe good for newer runners and longer more relaxed sessions for the more experience like myself. For the fastest of sessions I would of course recommend something much more minimal. However, the firmness of the midsole and the fulcrum make it easy enough to pick up the pace!

Charlie @ Northern Runner Newcastle

Other Considerations

Hoka Clifton : These have a softer feel to the cushioning and a narrower more pointed toe box. Hoka shoes have a rocker which is designed like the Fulcrum to aid in moving the runner forward. The fit and feel of these is the complete opposite to the Karhu Fusion 2. Here is our review:
https://www.northernrunner.com/blog/hoka-clifton-6-review/

New Balance 880: These have a softer feel to the cushioning. The propulsion system in these comes from the Freshfoam. This has bigger bubbles in the heel than the forefoot. This give the shoes a softer landing and a firmer toe off. The fit of the toe box is more pointy. Here is our review:
https://www.northernrunner.com/blog/new-balance-880v10-review-cushioned-road-running-shoes/

Topo Phantom: These are the broadest of Topo shoes and have a similar shape to the Karhu Fusion in the toe box. The cushioning is similarly dense to activate the feet on landing. Although the forefoot isn’t as flexible as in the Karhu Fusion 2:
https://www.northernrunner.com/search/topo-phantom

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