by Dave Hannaford, DPM
We ask our feet to absorb two to three times body weight with each stride…Our feet are remarkable. They accept this demand and even walk around after the race (sometimes pretty slowly).
The average ultrarunner lands on each foot about 5,000 times per hour (give or take a couple hundred). This number doesn’t change much with a slower pace, it just takes a lot more strides to finish the race, or training run. Studies find that the normal runner lands about 90 strides per minute, but my experience with ultrarunning reveals a slower average because of walking and fatigue; the above estimate includes that difference.
We also ask our feet to absorb two to three times our body weight with each stride. 5,000 strides times maybe 300 pounds (we are all skinny runners, right?) is 1,500,000 pounds per hour. Our feet are remarkable. They accept this demand and even walk around after the race (sometimes pretty slowly). Proper motion of the foot allows these forces to dissipate. This is why most feet don’t get injured. The problem is there is a huge variation from person to person in the quantity and direction of the motion and sometimes your feet can’t handle the demands. In high-mileage ultrarunning the feet have to be pretty close to optimal or pain and injury result. Every day in my practice I am amazed at sometimes how little is required to cure injuries which have been present for years. For many runners, a wedge the thickness of a nickel placed accurately can be enough, shifting the motion closer to optimal.
ACTIVE AND PASSIVE STRUCTURES
The foot is composed of 26 bones; some people have a couple more. These make up the foundation of our feet. Each of these bones has a coordinated function that is vital to the proper motion of the foot. The proper function of these bones is determined by the other structures within the foot and leg. There are small muscles within the foot that work in tandem with the lower leg muscles. Tendons in the lower leg muscles attach to the foot and pull the ankle and foot into appropriate positions for optimal structure and motion. These are the “active structures” that burn energy to do their jobs. Alone, they are not enough to keep the feet working. They need help from the least understood parts of our feet – the passive support system. There are small ligaments (connective tissue bands) that connect each bone to its adjacent bone. These are the structures that hold the bones in alignment and keep them connected to each other properly, but they aren’t nearly strong enough to hold the foot shape by themselves.
The other more functional passive structures are composed of connective tissue and extend throughout the foot and actually tighten and loosen without energy expenditure. They are triggered by the motion of the bones and muscles. These are tough fibrous tissues with poor blood supplies and slow healing capacities.
The notorious Plantar Fascia is the prime example. Notorious because of how often it is injured in ultrarunners. This is the most common foot injury I see. This band connects to the bottom of the heel bone and fans forward to the bases of the toes. It is actually an extension of the Achilles tendon that runs from the calf muscle down to the back of the heel. It attaches to the heel bone but is a continuous tissue that becomes the plantar fascia when it reaches the bottom of the heel. When you look at the back of a horse’s leg the big knob that is above the hoof and looks like a backward knee is like our heel bone – horses walk on what would be our toes. That knob has dropped down to touch the ground in our human foot. Knowing this helps our understanding of the plantar fascia. It is the spring that supports the arch and as the toes bend upward it tightens to raise the arch, making the foot solid and inducing proper push off.
Every foot is different and it is rare to find a foot that doesn’t have some inherent flaw in one of these tissues that can leave a person susceptible to injury. These structural risk factors can exist within a foot for many years and then all of a sudden appear as an injury when enough forces occur at one time that exceed the strength of that particular tissue. Increased mileage, fatigue, shoe faults, weight gain, muscle atrophy, poor daily wear shoes such as flat sandals, unfamiliar activity such as climbing ladders, age-related arch loss, and many others, may combine. Scientists have also noted chemical changes in the actual connective tissue with aging. If it sounds complicated it’s because it is.
This leads to the main purpose of this article: Injury prevention.
Let’s breakdown the running motion into parts, explain the potential injury each part can produce and discuss prevention.
CHOOSING SHOES (not really part of the gait, but a vital step).
Injuries include blisters, nail damage, too much and too little pronation (the amount the foot flattens and the ankle rolls inward with the weight on the inside of the foot). Shoes should be sized larger for ultrarunning. Remove the insert from a worn shoe and make sure there is about a quarter inch of new looking surface ahead of the smudge made by the tip of the longest toe and make sure the smudges of the entire tips of the fifth and big toe show and don’t overhang the insert liner. Otherwise try a different shoe size or shape.
Be sure that you choose your shoes from the motion category that matches your needs. Improper pronation can cause sprains, tendonitis, and injuries higher on the body such as knee pain. Usually neutral, stability, and motion control are the three. This is best determined by gait analysis because only the most obvious mismatches can be determined by shoe wear patterns. Lateral heel wear is normal. Shoes usually lean outward a little when they are worn out. Trail shoe categories are often hard to determine, so research them carefully before believing the manufacturer or falling for words like ”stable base”. Find a good running store, online source, or experienced running medical expert for advice.
Replace shoes before they become worn out. Trail shoe wear is hard to determine because the outer soles don’t show as much wear as road shoes. Good advice is to buy a new pair when the old pair is half-worn and take the new pair out for a test run periodically. When the new pair feels better, switch to them.
Trim nails frequently and use a file to bevel them at a declining angle from rear to front if they are thickened. Consider lubrication, pre-taping toes and feet (discussed in other UltraRunning articles, and covered very well in Fixing Your Feet, by John Vonhof), toe separator socks and lacing options if you have problems or extreme running conditions.
Nearly all ultrarunners strike the ground with their heel first. I have had many patients throughout the years who thought they hit their forefoot first, but video gait analysis nearly always shows them that they do not. Normal heel contact (this can change on steep hills or rocky irregular surfaces) is that the outside of the heel lightly strikes the ground and quickly rolls onto the rest of the foot. The knee should be slightly flexed and the front of the foot is just slightly higher than the heel at contact.
Injuries caused by improper heel contact include knee, hip, shin and back pain from the increased impact of an exaggerated heel strike, with the toes elevated and the heel absorbing force for a longer period of time before the rest of the foot. When the foot hits flat, neither on the front nor the heel, impact is also increased because of the braking action and inability of the foot to roll and absorb the force.
Try to think about how your foot hits the ground. Choose shoes that cushion the impact and help with the nice transition from heel to forefoot. This is very individual and varies based on differences between factors such as arch height, calf tightness, bow legs, body weight, and overall flexibility. Cushioned inserts and gel heel cups are helpful, but probably mask the real cure which is better running form.
FULL FOOT CONTACT
This is the portion of the stride that has the most consequences. The foot is supposed to elongate and spread to adapt to the surface and distribute the impact forces. Unfortunately it often elongates too much, spreads too much, and for many, twists too much while this is happening. The most common structure to suffer is the previously mentioned Plantar Fascia. If you pull your toes upward you can feel the band near the heel at the back of the arch. The pain often begins as heel pain because that’s where it connects, but it is really improper arch function that is the cause. Frequently the arch remains flattened too long, overloading and pulling the plantar fascia away from the heel bone slightly or stretching the fascia too much along its length since it is not getting any help from the muscles or bone structure.
Every muscle in the lower leg connects into the foot, so if the foot twists or stretches too much, it hurts the tendons and muscles of the leg. Achilles tendonitis, inner or outer ankle pain may result. Keep in mind that arch elongation, height of the arch, and shape of the foot are genetically determined and each type has its own normal range of motion. Flat feet do not necessarily have more problems than others.
There are two approaches to keeping the foot within its healthy range of motion: internal support and external support. Internal is simply maximizing the strength of the arch muscles by exercising the feet. Many people have feet that no amount of exercising can protect. The structure is just too unstable. These people need external support. A moderate amount of external support is safe and advisable for injury prevention, even in healthy feet. This external support may come from good shoe choices, over-the-counter inserts and if necessary, medical custom orthotics.
As a rule, in our Western culture we have weak feet. Other cultures have many fewer arch injuries. Because of this we should all strengthen our feet. My favorite, most practical, exercise is the “toe scrunch”. It requires no equipment and can be done any time. With shoes off strongly curl your toes downward to make a fist with them. You should see well-defined knuckles on top at the bases of the toes if your foot is working correctly. Arch cramping is a sign of weakness and means strengthening is very important. Hold the position for five seconds as hard as possible and repeat five times. This exercise strengthens the arch, not just the toes, especially if you keep your ankle at about 90 degrees to the leg as if you were standing.
While the foot is still flat on the ground and the other leg is swinging past it, the foot is supposed to become more erect, the weight shifts more to the outside and the foot becomes what is called a rigid lever. Supination (the opposite of pronation) and locking of the joints occurs so when the lift off and heel elevation begins there is maximum power and minimum stress on the various softer and weaker connective ligaments, fascia, muscles, and tendons.
If the foot does not lock with each bone settling tightly against each other like a picture puzzle, it suffers overload of these tissues and it’s just a matter of time before problems occur. Excessive pronation, weak muscles, poor shoes, and inherited faulty foot structure may prevent proper locking. Correct locking is visible in slow motion by a subtle shift of the foot to the outside just before and as the heel lifts. Gait analysts call this resupination. The previously-mentioned treatments aid with the prevention of this, but a significant number of people need orthotics to eliminate this risk factor. Typical injuries associated with this are knee pain, medial ankle pain, big toe joint pain, blisters along the inner edge of the forefoot, pain on the ball of the foot at the base of the second toe, and Achilles tendonitis because it is twisted instead of straight when the load on it is greatest.
You wouldn’t think that the foot could be at risk for injury while it is off of the ground, swinging through the air, but that is a very important motion. During the time the foot leaves the ground until the heel contacts again it is supposed to pronate slightly to prepare to accept whatever surface it strikes. If the foot is properly supinated as it leaves the ground it is easy for the swing phase pronation to occur. This is a natural reflex.
The ankle is in the process of bringing the inside of the foot downward so if irregular terrain occurs, momentum throws the force onto the stable flat portion of the entire foot. If the foot is pronated as it leaves the ground with the inside of the foot already turned downward, the foot will be supinating as it swings through the air and if uneven ground occurs it is likely the foot will continue supinating with momentum, throwing the foot outward onto the narrower outer portion of the foot – ankle sprains, knee pain, and leg fatigue are a common consequence.
This is why people who have pronated feet can cure ankle sprain problems by raising their arches even though this pushes them outward. The other swing phase error originates further up the body in the hips. Tight hips can cause the leg to swing in a circular motion instead of straight forward and straight back through. Iliotibial band injuries, low back pain, and hip pain result.
The final thought about swing phase motion is realizing that we all have different lower leg bone shapes. Often the left leg is different from the right. A way to test this is to stand facing a mirror. Make sure the knee caps are facing directly forward. The knee caps are part of the upper leg (thigh bone). If in this mirror image your feet point out (duck-footed) or in (pigeon-toed), it is because of the inherited twist within the lower leg bone. It is quite common that one foot is turned more than the other.
Anatomists tell us that ten degrees of outward position is normal, but I have found that the range is much greater. It is good to know this because when you run properly and swing your leg forward for heel contact your foot should point outward or inward similar to what is seen in the mirror. If not, you are turning your knee and hip. This can cause problems, so my recommendation is to go with your anatomy and don’t fall victim to trying to correct to a straight foot position if you weren’t born with it.
In conclusion, I hope this has helped clarify what a complex structure the foot is and complicated process running is. The more we are able to visualize what is happening when we run, the more we can intervene and take action to prevent and treat injuries. We can also decrease foot fatigue and improve tolerance for the extreme demands our feet are under for this sport we have chosen. Happy healthy running!
Dave Hannaford is a Podiatrist in San Rafael, California and an ultrarunner. Among his many athletic accomplishments, he has completed the Western States 100 and the Badwater 135.