The case for cross-training, part 6: Shoe and foot science

This six-part series is adapted from Matt Fitzgerald's forthcoming book, "Runner's World Guide to Cross-Training." Part 1 begins here.

Running shoes are indispensable to protect your feet from hard surfaces, cold air, and the like. But they also have certain disadvantages.

Fortunately, however, you can counteract these disadvantages with some special cross-training methods designed to enhance the performance of your ankles and feet.

The actions of the foot during barefoot running are highly complex. The actions of the foot during shod running are decidedly less so, because shoe structure constricts them.

Running shoes essentially force the foot to function as a rigid, two-part plank with a single fulcrum at the ball of the foot. There are several unfortunate consequences of this constriction, but perhaps the greatest is that it greatly reduces the amount of thrusting force that the forefoot and toes are able to generate in the last segment of the push-off.

The metatarsophalangeal (MP) joint at the ball of the foot was designed to actively plantar flex (flex downward) during push-off to squeeze a last bit of thrust out of this phase of the stride. Shoe structure does not allow the MP joint to actively plantar flex.

The resulting loss in force generation is analogous to the loss in vertical jumping height you'd experience if forced to jump without flexing your ankles.

In addition, because shoes do not allow us to use our little foot muscles the way they were designed to be used, over the long term they cause these muscles to weaken, so that they're less useful, shod or unshod.

Furthermore, all that cushioning in running shoes reduces the ability of your feet to "feel" the ground (called proprioception). Consequently, your feet are unable to feed your brain as much useful information with which to fine-tune your stride.

The result is slower reaction times in response to irregularities in the running surface and also higher levels of muscle activation, because the muscles, in a sense, have to be braced for anything. This bracing effect costs energy and increases tissue strain.

Here are some things you can do to address these problems.

Walk barefoot

Get in the habit of not wearing shoes when you don't have to. Remove your shoes in the entryway when you come home. Walk your dog barefoot when weather permits. Don't start with a two-mile walk on asphalt, though. Either stick to soft surfaces like grass or ease very gradually into walking on harder ones.

Do balancing exercises

Any time you challenge your ability to stay upright -- either by standing or moving on one foot or by standing on an unstable surface -- your feet and lower leg muscles work overtime to maintain balance and thereby become stronger.

Balancing exercises also develop proprioception. The single leg squat and pillow balancing exercises described in part 2 of this series are excellent strengtheners of the feet and ankles and enhancers of proprioception.

Balancing on a wobble board is another good one. Wobble boards are available at many running specialty stores for between $40 and $110.

Wear flexible running shoes

Some shoes are a lot more flexible than most others and allow the foot to move more naturally. Shoes with less cushion and stability are by and large more flexible.

Racing flats tend to be the most flexible running shoes. Runners with fair to good biomechanics should do a small amount of their training (specifically their high-intensity training) in racing flats or lightweight trainers to develop their push-off power from the ankle down.

To develop it further, you can begin to do some of your easy runs in flexible shoes too. This option is not for everyone and should be pursued with great caution by anyone who cares to try it.

Take it very gradually, paying close attention to the comfort of your feet and any developing aches and pains. There are some elite runners who do all of their training in racing flats, but of course they are very light and have nearly perfect biomechanics.

Even if you find that you are able to emulate them with great success, I'd still recommend that you do your longest runs in shoes with more cushioning, because your body's ability to absorb impact forces deteriorates as it fatigues.

Shoe manufacturers have recently begun to make training shoes that are designed to allow plantar flexion at the MP joint. The very first to hit the market was the Nike Free 5.0.

The average runner is advised to run just a few miles per week in these shoes in order to strengthen the feet, but runners with good foot and ankle stability can safely use these shoes for everyday training.

Run barefoot

There is a full-fledged barefoot running subculture within the larger running community. Its members prove that even people who grew up wearing running shoes can reach a point where they can safely do all of their running barefoot if they proceed sensibly.

I'm not asking you to do that. But I do recommend that you try to do a small amount of barefoot running on soft surfaces to strengthen your feet and ankles. Even doing two sets of barefoot strides per week on a grass soccer field will probably be of some benefit.

If you have access to a beach or golf course you can do complete barefoot running workouts on them. If you own a treadmill you can run barefoot on it once a week or so.

Start by walking barefoot on the treadmill, then after a week or two advance to no more than 5 minutes of running at a time.

Increase the amount of running very gradually until you're comfortably able to do normal running workouts on the treadmill.

Part 1: Intro to cross-training

Part 2: Strength training

Part 3: Stretching

Part 4: Non-impact cardio training

Part 5: Form training

Matt Fitzgerald coaches runners and triathletes and is the author of "Triathlete Magazine's Complete Triathlon Book" and "Runner's World Guide to Cross-Training."

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