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I know what you’re thinking- “But it’s summer” and “they’re so comfortable” and “so easy to take on and off”, or “Mine have a special arch support so they support my feet”, right? Well, they’re awful for your feet! And can cause a whole host of problems up the chain of your body, including knee, hip and low back problems. It’s one thing to do the short walk from the locker room to the pool with flip flops on but, quite another to be walking around, shopping and running errands in them for miles/hours.

As I discussed in my Bulletproof Runner Workshop a couple of weeks ago, ankle and foot mobility and stability are extremely important for long distance runners. In particular the 1st ray or the big toe needs to have enough extension (bend up towards the sky when you’re foot is on the ground) in order for the runner to have adequate push off with good alignment. If you don’t have enough big toe extension, then you’re likely to spin your heel either inward or outward aka “heel whip” which can wreak havoc further up the chain due to rotational forces exerted at your knee, hip and spine. You may also develop hallux valgus or bunions on the inside of your big toe or Achilles tendinitis (or tendinosis) from the abnormal spin on the big toe and heel where the Achilles tendon inserts.

When you wear flip flops, it causes you to essentially “grip” with all of your toes to keep the sandal on which is the opposite of how our feet were designed to walk. It’s often the culprit with the development of “hammer toes” where the middle knuckle of your toe sticks up and rubs against your shoe, causing blisters and pain. If you walk around all day in flip flops, you’re basically shortening/tightening your small intrinsic foot muscles (small muscles that start and end in your feet), your larger extrinsic foot muscles (the muscles that start in your shin and end in your feet), your plantar fascia and not allowing your feet to operate the way they were supposed to.

Intrinsic Foot Muscles

Extrinsic Foot Muscles: Note the highlighted Peroneus Longus attachments from outside of knee to underside of 1st ray (under big toe).

Because your body, fascia and muscles are so interconnected, a foot dysfunction can quite easily lead to a knee problem. If you look at the highlighted muscle in the above picture, the peroneus longus, it starts up high on the outside of the knee (fibula). This is also one of the attachments of the infamous iliotibial band (ITB) that every runner attempts to “stretch out” by rolling on the foam roller. Well, this ITB is continuous with the lesser known, Tensor Fascia Lata (TFL) muscle which starts up at your hip which of course is connected to your spine. So, now your foot problem can travel up to your knee, hip and spine. Btw, your foot may be totally pain-free but your back could be screaming at you! I had a patient a few years ago who came to see me after her spine surgeon referred her. She had severe back pain every time she got up and down from a chair, walking and bending her spine also hurt. She had spent 3 days walking around in flip flops while on vacation at the beach. Her feet felt fine but her back hurt and we were able to trace it back to the way she was walking with the flip flops, screwing up her feet and everything up the chain with every step she took. So where I’m going with this? This brings us to the idea of “Regional Interdependence”, a concept I was introduced to by Gray Cook. It is the concept that “seemingly unrelated impairments in a remote anatomical region may contribute to, or be associated with the patient’s primary complaint.”

So, even though it appears that your flip flop wearing habit is totally harmless, it’s probably doing you more harm than good and may even be the cause of your knee or back pain. So, just say no to flip flops. Your feet, knees, hips and spine will thank you!