Why Runners Should Never Wear Flip Flops

Could your shoe choice lead to a sports injury?

Most of us greet the summer with the beloved flip-flop. Becoming ever more popular, the flip-flop is a summertime staple. Rainbows, Reefs and Havanianas have become as trendy as the winter Ugg boot. But like the Ugg boot, the flip-flop has no ‘nutritional value’ to the runner, or the average person. There is no support and no structure.

Use of the flip-flop requires active muscle recruitment. Of course it’s good to actively use muscle, how else would we strengthen a muscle without using it? However, overuse is a different story.

The foot uses several muscles to hold a flip-flop on. Without these muscles working, the flop would literally flip off the foot completely. Mainly, we use the flexor muscles of the foot, the ones responsible for flexing the toes and ankle. Firing these muscles is what grips down on the flop, as seen when we ‘curl’ the toes. We use these muscles with every step, usually without realizing.

Imagine, if you will, hanging from a pull-up bar. Eventually the wrist and hand muscles fatigue and we are forced to let go of the bar. The wrist and hand flexor muscles are contracting isometrically. The fingers are curled. There is no movement, but a constant contracted state. As we walk in flip-flops (and any other shoe without a back), we are forcing our foot and toe flexors into a constant isometric contraction. That state eventually becomes fatiguing.

The problem with fatigue, besides the obvious decline in performance that results, is the eventual tightening of the muscles. When a muscle or group of muscles is in a contracted state for long periods of time, it tends to grow tighter and tighter. A tight muscle cannot generate the most muscle force for a good contraction the way a normal muscle can. Thus performance decreases again.

These main muscles that are affected by the flip-flop happen to sit right behind the gastroc-soleus complex, that group you know of as the “calf” muscles. Underneath these muscles is where the muscles that flex the toe and ankle live.

In reality, both the gastrocnemius-soleus complex and the rest of the ankle and toe flexors are affected by isometric contractions from a flip-flop, but because the latter group is significantly smaller in terms of length and girth, these muscles are extremely more likely to be negatively affected. By contrast, the calf is generally stronger and more resistant to fatigue, especially in a runner.

This entire group, the calf and the rest of the flexors, makes up the so-called posterior compartment. As most of you may have experienced, the posterior compartment is often the site of fatigue, tightness and subsequent injury. We know what it’s like to feel tight or tired or have less power or ‘push-off’ from the back of our legs. What you may not know is that most foot and ankle pain can also be blamed on this muscle group, everything from calf tears and strains, plantar fascitis to peroneal, posterior tibial or achilles tendonitis or 'shin splints', tibial stress syndrome and even stress fractures.

To add to this, the posterior complex becomes tight and tired because it is constantly in use, even in a good shoe! Walking, stairs, not to mention running, puts miles on the calves. Like a car hitting its 10,000 mile check-up and beginning to break down, so do our calves become tight and tired as we pile mileage on over the years or through a training program without a check-up of sorts— some stretching and maybe even an occasional sports massage. Hill and speed work can speed up this process considerably, which is why the first signs of injury often appear after speed work.

Most especially for those of us that live and work in commuter cities, just taking the subway daily, hiking up at least 30 stairs and trekking 10 blocks back and forth on the pavement can wreak havoc on the posterior compartment. Then we likely sit at a desk and our legs lay dormant for hours, tightening up and losing circulation.

Now go for a run. What we find is that this group is already overworked and tired, and we are expecting it to contract and develop power to get through our activity.

Imagine if you worked as a painter and contractor all day. You would use your arms half of the day; hammering overhead, holding large planks of wood, lifting, using power tools. Your arms would be extremely tired by days end; after all, you used them excessively all day, then did the exact opposite. Now imagine if your hobby was baseball or tennis? How do you think your arms would be able to perform after hours of activity all day? Simple, they want more rest, not more work.

The same is true for our posterior compartment. The last thing they want every day is to power your lower body after having worked so hard they tired themselves out. They are tired and as a result, tight. Far be it for us to take care of them with plenty of water, frequent massage and lots of stretching every day, pre and post run.

So, getting back to the flip-flop. Why put on a shoe that makes the posterior compartment have to work harder? Can’t we just give them a rest? Isn’t that what ‘recovery’ means? After all, that’s what they are asking for. By putting on a flip-flop, you are not only denying your posterior compartment the rest it deserves, you are asking it to work harder and in a dysfunctional manner. You are doing yourself and your next run a huge disservice.

This summer, be a smarter runner. Find a summer shoe with a back strap or laces. Wear a shoe that holds tight to your foot, not a shoe that forces your foot to hold tight to it. Also note, Birkenstocks are back in fashion! These are a great alternative to the flip-flop and have great arch support as well!

Any less your foot can work just means it can work harder on your next run because it is able to rest and recover!

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