When the foot hits the ground, your lower body performs a complex series of joint and muscular reactions to help keep you upright, move you forward, and absorb shock (originating from a 2-3x increase in body weight moving through your foot while walking). With summer bringing warmer weather, our clothing - including our footwear - will change. This change in footwear correlates to a change in how we walk. One common summertime feature is flip-flops. Flip-flops can have a negative effect on walking, and thus be a contributor to lower body injuries. Rather than asking you to stop wearing flip-flops (which I personally have not done yet), let's educate ourselves so we can make an informed decision on what to wear, how long to wear them, and possible alternative solutions.
Walking can be broken down into two phases: Stance and swing. Stance is when one or both feet are on the ground, and swing is when the foot in in the air. Stance makes up about 60% of this cycle, and can be broken down into five stages.
1. Heel Strike:
This is when your heel first touches the ground.
2. Early Flat Foot:
This is when the body is moving forward and the ankle moves into a neutral position. The end of this phase is when the body's center of gravity passes over the top of the foot. The goal of this phase is for the foot to be a shock absorber as the weight moves forward.
3. Late Flat Foot:
This phase is when the center of gravity is moving forward toward the toes and ends when the heel starts to rise off the ground. In this phase, the foot transitions from being a more flexible shock absorber to one which is more rigid, giving the body leverage to move forward.
4. Heel Rise:
This phase is when the heel is rising while the foot continues to be a rigid lever to allow the body to propel forward. During this phase, the foot can experience double to triple the force of a person's body weight moving through it.
5. Toe Off:
This phase is when the toes leave the ground. Ideally, you are pushing through your toes, including your big toe. This phase can be considered the beginning of swing phase.
Now that you can know the basics of walking, walk and see how you move through your foot. Do you land on your heel, roll through your entire foot, feel your heel rise? Are you beginning your swing before you roll through your big toe? The next question is what you are wearing on your feet - if you are wearing anything at all! Compare how you walk in different footwear. Now, back to flip-flops - why should you be more aware when wearing them? The answer is that the loading pattern through your foot will be different, and can affect the biomechanics to your knees, hips, and back. For instance, in order to hold flip-flops on your foot, you must tighten up the underside of your foot and curl the toes. Even if you are heel striking and rolling through your foot, you will not be loading optimally because you are loading on an altered foot that's gripping your shoe. The best shoe for you is one that is supported on your foot. This is so all of the muscles involved are doing the job they're designed to do rather than trying to hold footwear in place.
So should you get rid of flip-flops? I cannot answer that for you. However, recognizing the changes they make to your mechanics, you should think twice before wearing them for long periods of walking AND promise yourself that you will stretch your feet and legs to help offset the extra work.