Qualitative thoughts about running form

Built to Run: If you have been convinced by the science that upright-walking humans are formed over time to be the ultimate long distance running machines in dry hot weather.  If you have not heard this hypothesis and its supporting evidence, please click here.



Running Form: With a rudimentary understanding of human anatomy we can make some assumptions about the running form most conducive to our structure.  Some of the action verbs required to run:

• Twist - the trunk 
• Swing - legs/arms
• Reach - reach in front and bhind
• Absorb - landing, absorbing the momentum down loads the springs of the body 
• Propel/Push-Off - propel over the landed foot, and extend legs, toe off.

Big to Small: Always tackle a problem big-to-small.  Working on the assumption that the biggest muscles need to bear the biggest loads.

1. The glutes:

"The gluteus maximus is the largest muscle in the human body. It is large and powerful because it has the job of keeping the trunk of the body in an erect posture. It is the chief antigravity muscle that aids in walking up stairs."

The glutes do two things: keeps you from folding in half like a pocket knife and pushes your thigh from a raised position to a lowered position (sitting to standing).  If you have good upright, "hips-open" posture when running, you can dedicate this muscle group to absorbing and propelling the leg down and back.  If your posture is bad, you engage the glute to keep you from folding in half.  The glutes need to share their capacity to maintain your bad posture AND run.  The strongest movement of the glutes is pushing back - this is what propels you forward.  Try to fire this muscle when it contributes most.  The glutes are ~25% of your running muscles, make them do 25% of the work.  (25% pulled from the sky.)

   2.  The quads:

The next biggest cluster of muscles and cetrtainly the longest.  The Quads is an eccentric powerhouse, it absorbs your landing, turning all that downward momentum into stored energy.  The quads stops you from collapsing and in contraction straightens your leg.  It is the heel-cushioned running shoes that incorrectly allows you to straighten your leg WAY too soon.  Landing with knees slightly bent stored the most energy, straightening the leg should happen at push-off, firing simultaneously with the glutes.  It's the one-two punch of propulsion.  The quads are ~20% of your running muscles, make them do 20% of the work.  (20% pulled from the sky.)

  3. The trunk:

Twisting the trunk is often over looked.  We coach pitchers, batters, boxers, golfers, etc to originate motions in the hugely muscled trunk.  A perfect punch begins at the foot, twists the hips, twists the trunk extends the arm.  The arm is a messenger of the forces generated from the 'big boys' of the muscle groups.  Running is the inverse of that.  A trunk twist turns into a foot motion.  Twisting the trunk allows the reach portion of the running stride and extends the push off out the back.  The more the twist, the longer the stride (at the same cadence).  I think of the 'X' created by the shoulders and hips when I'm driving my knee forward and pushing out the back.  Arm swing exists only to engage this twisty spring mechanism.  The trunk is ~15% of your running muscles, make them do 15% of the work.  (15% pulled from the sky.)

4. The hamstrings

Next on the size-matters comparison is the hammies (I told you, conversational tone, this is no kinesiology class).  Hamstrings do the opposite of the quads, and fold the leg to make the knee drive easier.  The torque on the hip flexors during the swing phase is a function of leg weight AND leg length.  You can't lighten your leg, so make it shorter by folding it.  Engage hammies to bend the leg before (or syncopated) to leg swing forward.  This is why leg-swing-forward is referred to as knee-drive, not foot drive.  Hip flexors getting sore?  Try engaging hamstrings sooner! The hamstrings are ~12.5% of your running muscles, make them do 12.5% of the work.  (12.5% pulled from the sky.)

       5.  The gastroc chain

Shorten to 'the calf'.  Absorbs energy eccentrically allowing the heel to drop to the ground in a controlled manner.  Energy return happens at push off.  If you raise your heel with heel cushioning in your shoes then you're reducing the effectiveness of this energy return mechanism.  This is why people that transition to minimal shoes or barefoot in one day complain about calf soreness.  these > 1 inch heel raises in shoes limits the calf range of motion from 5-10%.  (reminder, if you see a '%' then the number is pulled from my rear, i meant he sky.)  The calf is not a muscle used to push the body in the air at push-off, it's relatively too small. Absorb, hold, return - it's due to fire at the end of the glute/quad firing and just before the hamstring folds your leg.  This phase in the running sequence is sometimes referred to as toe-off. Calves sore? Try lifting the foot with heel and forefoot at the same time - lift your foot flatfooted. The calves are ~7.5% of your running muscles, make them do 7.5% of the work.  (7.5% pulled from the sky.)

 6. The foot

Almost a copy paste from above, the foot muscle contribute a small but necessary component in the absorb/release phases.  Most important is that the foot is thought to contribute ZERO, so strap them to an unmoving slab of wood (eg 'supportive' shoe).  We ignorantly turn off any foot contributions by selecting the wrong shoes.  Let the arch load eccentrically and return it's share to the push off, that's what it's for!  The feets are ~5% of your running muscles, make them do 5% of the work.  (5% pulled from the sky.)

        7.  Others - supporting muscles that help (sometimes hinder) the balance and movements of these larger groups.  The shoulders, traps, glute medius, muscles for balancing, muscles for left-right (frontal plane) movements comprise the rest.

Summary: Asking too much from a smaller muscle group will limit your performance or distance quick!  Having an awareness of what's getting tired, sore or hurt will give you clues of what groups aren't pulling their weight.  Practice mindfullness with your runningfullness!  Remember, endurance isn't how hard a muscle can work - it's as much turning off the muscle groups when not in use.

Developing the entire chain

It would probably be a good idea to dedicate a series of posts to kinetic chain development, but I just need to get this thought out there.  Especially in light of Vibram settling a law suit suggesting strength of muscles reduces injury.

When I was a silly body-building weight lifter, tracking diameter of biceps (seems so silly).  I would target muscles and do isolating exercises to make them stronger (again, very silly).  Some muscle groups responded well, others not so  much.  I struggled to know why.  

For example, thin wire'y calves.  Lifting tons of weight on a calf-raising machine made no difference in large calf muscle size.  Besides the obvious 'who cares', I thought I narrowed the reason why.  The calf is a link in a chain.  You can't make certain links of a chain stronger than others, it makes no sense.  My Achilles tendon (through genetics? or whatever the reason) was as small as a #2 wooden pencil.  People with large calves had thick thumb-width Achilles.  

After a few years of running, using thin (or no shoes) my calves are getting functionally stronger BECAUSE the entire chain is strengthening.  As you'd expect, my Achilles tendon is two times thicker.  Tendons, ligaments, bones, muscles: they all react and adapt.

Adaptation is a reMARKable thing.  

A good source that describes bone mineral density, tendon and muscle adaptation, check out  the book 'Brain Training For Runners'.

MAF Test and Training Summary

On the Facebook group, and people I am coaching we have a few participants doing an aerobic test called a MAF test.  Some are logging their performance here LINK.

The 180 Formula (To find the maximum aerobic heart rate):

1. Subtract your age from 180 (180 – age).

2. Modify this number by selecting a category below that best matches your health profile:

a. If you have, or are recovering from, a major illness (heart disease, high blood pressure, any operation or hospital stay, etc.) or you are taking medication, subtract an additional 10.
b. If you have not exercised before or have been training inconsistently or injured, have not recently progressed in training or competition, or if you get more than two colds or bouts of flu per year, or have allergies, subtract an additional 5.
c. If you’ve been exercising regularly (at least four times weekly) for up to two years without any of the problems listed in a or b, keep the number (180 – age) the same.
d. If you have been competing for more than two years duration without any of the problems listed above, and have improved in competition without injury, add 5. 

 For example, if you are 30 years old and fit into category b: 

180 – 30 = 150, then 150 – 5 = 145.

During training, create a range of 10 beats below the maximum aerobic heart rate; in the example above, train between 135 and 145 staying as close to 145 as possible.  Track you MAF tests weekly or biweekly for 3 months.  When you see a plateau you can switch to speed days, hill climbs, real anaerobic stuff. *

Perform the MAF Test on a track, (or repeatable surface) running at the maximum aerobic heart rate. A one- to five-mile test, with each one-mile interval recorded, provides good data. The test should be done following an easy 12–15 minute warm up, and be performed about every month throughout the year. Below is a 5-mile MAF Test of a runner training at a heart rate of 150:

 Distance Time (min:sec)
 Mile 1     8:21
 Mile 2     8:27
 Mile 3     8:38
 Mile 4     8:44
 Mile 5     8:49

During an MAF Test, it is normal for the running times to slow each mile – the first mile should be the fastest and the last the slowest. If this is not the case, it may indicate the lack of an effective warm up. In addition, the test should show faster times as the weeks and months pass. For example, over a four month period, we can see the endurance progress in the same runner from the above MAF Test. Note the aerobic speed improvement between April and July:

             April   May    June   July
 Mile 1   8:21   8:11    7:57   7:44
 Mile 2   8:27   8:18    8:05   7:52
 Mile 3   8:38   8:26    8:10   7:59
 Mile 4   8:44   8:33    8:17   8:09
 Mile 5   8:49   8:39    8:24   8:15

This improvement is typical during the aerobic base period. Some improve at a faster rate, others slower.  Most importantly, if you’re not improving within a three- or six-month period, it means something is wrong.  It may be a dietary or nutritional factor, excess stress, overtraining (such as too many miles), etc. In some cases, it may be the maximum aerobic heart rate is too high (often from choosing the wrong category in the 180 Formula).  Moreover, a reversal of aerobic function, i.e., slowing of aerobic pace during base training, may indicate an impending injury – enough of a reason to perform the MAF Test regularly.

Progress should continue in some form for three to six months or more before aerobic benefits may reach a normal plateau. Adding anaerobic work to the schedule before this plateau may impair (and ultimately even reverse) further aerobic progress.

The greatest benefit of the MAF Test is that it objectively demonstrates aerobic improvement in the form of aerobic speed. These changes also reflect competitive improvement.

© 2007 Philip Maffetone www.philmaffetone.com

*If you see NO improvements over 2 or 3 MAF tests, there's something in your training, diet or other stressors that is affecting your aeorbic performance.  email me and we'll figure it out! 

Are You Ready to Go Minimal?

Jay Dicharry the author of:

  

Weighs in on criteria conditions needed to try out minimal shoes using mobility test (with nice fixes to improve), muscle isolation, leg-stance balance, posture alignment.  It's a great 7mins, if you dig his stuff, buy the book for more.

Note... Even after practice, I can NOT stand on one foot with my eyes closed, I tip over as if pushed!  Let me know if you can do it!

Overuse Injuries

Oh how i enjoy taking two sides of an issue to see which explanation is the more supportable (it's a science thing).  Sometimes the counterintuitive explanation is the correct one.  Knowing this, and knowing 'words have meaning' - we enjoy picking apart words, diagnoses, explanations, etc…

We can't help but chuckle when hear the term "overuse injury" used to 'describe' running injuries.  In googling it (in quotes) gives you about 83,500 results.  The top 3 are definitions.  

sportsmedicine.about.com  Definition: Chronic pain and injury refers to the sort of physical injury, ... are sometimes referred to as cumulative trauma or overuse injuries. 

emedicine.medscape.com  Overuse injuries, otherwise known as cumulative trauma disorders, are described as tissue damage that results from repetitive demand over the course of time. The term refers to a vast array of diagnoses, including occupational, recreational, and habitual activities. 

http://medical-dictionary.thefreedictionary.com/ Overuse injury
Sports medicine A sports- or occupation-related injury that involve repetitive submaximal loading of a particular musculoskeletal unit, resulting in changes due to fatigue of tendons or inflammation of surrounding tissues; OIs include tennis elbow and golf elbow. 

From emedicine: "cumulative trauma" sounds more like blows from a hammer than feet landing on the ground doing something as natural as running.  We assumed these definitions might be silly because it is so common to describe running as feet slamming on the ground, or pounding the pavement.  But obviously, some of us realize running has been with humans for millions of years - an adaptation used to survive.  Running is as natural to humans as breathing, or the muscles used to balance or stand; or having a beating heart.  These are muscle contraction too and not likely to hurt or be sore due to 'overuse'.

If you've been running non-stop since childhood with a form that is natural to the variable compliances of the muscles and tendons at your natural cadence with appropriate protection yet proprioception- we DOUBT seriously that you'll have an injury from overuse!!  It's more aptly an issue of underuse.

An explanation or diagnosis of an injury, condition, whatever must have the distinction between proximal cause, ultimate cause, fundamental cause.  There are chains of causes some proximal, some ultimate.  Some medical professionals have fancy terms for things that nothing more than a regurgitation of the symptoms.  " i have pain in my foot arch"  "oh you have plantar fasciitis"   which is what you said to them!  

Example: 

I am hurt due to an inflammation of a tendon, that's proximate.  The tendon is inflamed because of a muscle imbalance, that's an ultimate cause.  There is a muscle imbalance because of a form issue, biomechanics, leg length discrepancy, neuromuscular disconnect, or simply NO feedback mechanism of your bad form due to your overly cushioned shoes.  

Think about it, and don't settle for lame diagnoses.  

Footwear Trends: Should Sport & Fitness Enthusiasts Embrace the Minimalist Movement?

Link Here:

Footwear Trends: Should Sport & Fitness Enthusiasts Embrace the Minimalist Movement?

ISSN: 1543-9518

---

Danielle (Perkins) Holsomback & Kayla Peak

ABSTRACT

The popularity of the barefoot movement in sports and fitness activities has soared within the past few years as evidenced by a growing community of minimalist
footwear enthusiasts wearing the ‘glove’ shoes in their sporting endeavors, fitness workouts, and everyday leisure activities. This emergence
of the minimalist shoes, such as the Nike Free© and Vibram FiveFingers®, has created a wave of intrigue for those sport and fitness enthusiasts wanting
a natural running experience without being subjected to the hazards of the road. Whether running barefoot, in shoes or in minimal footwear, the trends in footwear
preference have caused much debate between researchers as to which form causes more injuries and/or best serves to enhance athletic performance. As sport and
fitness professionals, it is important to thoroughly examine the current footwear trends to develop a ‘best practices’ approach for advising our athletes
and clients.

Click above link for entire article.  It is a great summary of minimalist footwear.

Ticking Time Bomb, How Children's Shoes Cause Problem Later in Life

15MAY/11Off

Ticking Time Bomb, How Children's Shoes Cause Problem Later in Life

What's wrong with this photo? Plenty! The young boy's shoes will screw up his gait and cause muscle imbalance. And he's stretching!

by Dr. Phil Maffetone

Twenty years ago, a review of shoes and gait in the journal Pediatrics outlined some key factors that affect children’s feet. Pediatric orthopedist Lynn Staheli, M.D., from the Children's Hospital and Medical Center, Seattle, Washington, listed these important points:

1.) Optimum foot development occurs in the barefoot environment.

2.) Stiff and compressive footwear may cause deformity, weakness, and loss of mobility.

3.) The term "corrective shoes" is a misnomer.

4.) Shoe selection for children should be based on the barefoot model.

5.) Physicians should avoid and discourage the commercialization and "media" obsession with faddish footwear.

6.) Merchandising of the "corrective shoe" is harmful to the child, expensive for the family, and a discredit to the medical profession.

The Nike V Infant toddler shoe.

Perhaps the most offensive aspect of the footwear industry is the harm it deliberately inflicts upon unsuspecting children by encouraging them to wear bad shoes. Between the twin forces of television and parental encouragement, little Johnny or Jill are defenseless. In particular, there's the potential damage to the young developing body and brain. And, this could be a primary cause of physical imbalances, injury and disability and later as adults.

It was evident from Dr. Staheli’s article that shoe companies in 1991 were already heavily marketing unhealthy children’s shoes, playing on the parent’s emotions and those of older children. Today, shoe companies continue to use clever million-dollar advertising campaigns to encourage kids to ask for, and parents to buy, harmful shoes. And it’s obviously successful. The U.S. children’s footwear industry, which includes shoes for kids up to 16 years of age, generates over $5 billion annually, where products are made for cuteness and style rather than function.

What’s the best shoe for your child? None—barefoot is best and nothing comes close. Children should be barefoot, most, if not all the time. This provides the optimal stimulation of the foot by the ground, which helps train the brain for proper gait and other natural movements that children require from the start.

When a shoe becomes absolutely necessary, Dr. Staheli says it should be lightweight, flexible, shaped more or less quadrangularly, and should not have arch supports and stiff sides. She says that pediatric orthopedists strongly oppose "corrective" or "orthopedic" shoes for straightening foot and leg deformities like flat feet, pigeon toes, knock-knees, or bowlegs, claiming there’s no evidence that these so-called therapeutic shoes are effective. Instead most of the supposed deformities in children naturally correct themselves. How you might ask?

Being barefoot is the best way for that to happen. Most healthcare professionals who properly understand a child’s body mechanics know this. (Yet there are many “experts” who recommend the regular use of shoes for young children, but they are usually aligned with the shoe industry or companies making orthotics and other corrective devices.)

Any shoe has the potential to seriously disturb the gait of a young child. His or her sensitive feet sense footwear much more than the adult foot. Even relatively minor pressure on a child’s foot from a shoe can begin deforming it, leading to a permanent problem.

During the first year following the acquisition of independent walking, most of the child’s gait activity, in particular, the neurological memories—the communication between brain and body—becomes well established.

Barefoot is best for children.

During this time, if the feet are not allowed to develop well, gait and balance disorders begin to occur. In many children, these irregularities are often subtle (the “clumsy kid”) while others more serious such as increased vulnerability to physical injury and various neurological imbalances anywhere in the body, including those associated with eye movement.

The full development of a child’s balance and compensatory mechanisms, and overall gait mechanics, takes years to mature. While the first five years of life are most delicate, neuromuscular interference from footwear can occur at any and every stage along the way into early adulthood. This can lead to more serious and chronic physical imbalances later in life, such as a running injury or back pain, and even amplify the stress caused by imperfect shoes.

Earlier this year, Caleb Wegener, Ph.D., and colleagues from the University of Sydney, Australia, reviewed the problems associated with a variety of different shoes worn by children for walking and running. Their study, published in the Journal of Foot and Ankle Research, states that, “Shoes affect the gait of children. With shoes, children walk faster by taking longer steps with greater ankle and knee motion and increased tibialis anterior activity. Shoes reduce foot motion and increase the support phases of the gait cycle. During running, shoes reduce swing phase leg speed, attenuate some shock and encourage a rearfoot strike pattern.” In short, these are some of the specific items that are a recipe for physical and neurological disaster, and the start of a process of chronic injury and disability that could last a lifetime.

These researchers noted Dr. Staheli’s 20-year old suggestion that shoe design should be based on the barefoot model. But some of the shoes they tested were designed on these principles and still caused gait irregularities in children. 

The researchers also state that, “Further attention could also be paid to reducing the weight of shoes which may be responsible for some of the [abnormal] changes found in children’s walking and running gait.” (It’s interested that this type of “free” information is available to shoe manufacturers but may never be utilized—instead, they test their shoes on machines, not real people.)

Among the untold problems that wearing shoes can impose in the developing child is the impact on the brain. From a baby’s very first delicate steps, each walking and running gait pattern significantly influences brain development. These actions affect lifelong patterns in the nervous system, even beyond the gait and balance mechanisms—they include postural habits, the ability to compensate to physical stresses, and the growth of muscles, bones, ligaments, tendons and other tissues. Normally, with each muscle contraction and relaxation, and every joint movement, important neurological patterns are created by the brain, just like with any memory. Shoes distort this process, and instead, the brain learns and designs irregular patterns of movement throughout the body.

Most childen's shoes are health hazards. It's like handing them "smokes"-- which is what candy companies did for many years.

In addition, other areas of the brain can be impaired. Normally, during early development in children, all the important neurological input from body movements trigger increased blood flow throughout the brain. This brings in oxygen and many other necessary nutrients to promote growth and development in areas that include learning, speech, and memory. Without the natural muscle contraction in the feet, for example, especially in the very small immature muscles that move the toes, impairment from wearing thick, oversupported modern shoes can reduce the brain maturing process.

In children plagued with posture- and gait-related problems, avoiding wearing shoes is even more important. This can help stimulate the above-mentioned neurological functions, which can, in itself, be very therapeutic. Rather than attempting the use of “corrective” shoes and related devices, such as inserts or braces, finding and correcting the causes, including  neuromuscular imbalance, is important.

Many physical ailments in adults could begin at this young age. Think about all the physical problems you’ve had in your life—it’s possible that many began during development of the important brain-body mechanisms due to significant interference by shoes.

It seems silly to even be discussing the issue of children’s shoes. Most people don’t question the fact that eating junk food is bad for kids, or smoking cigarettes. The level of brain and body stress from wearing bad shoes can be just as damaging. The most logical, effective, and healthiest way for children to develop their whole body is by being barefoot.

This essay originally appeared on Dr. Phil Maffetone's website. For more information on the do's and don'ts of children's shoes, Dr. Mark Cucuzzella has a lot more on the kids page on hisTwo Rivers Tread website. 

Foot Strengthening by Mobility WOD

K Star and Brian fly through these mobility movements that are great lower leg looseners.  Watch this video a few times to get the gist, and find your own nightly mobility movements that work for you.  

Crossover Gait

Just be more stable!  The first time I considered where (in relation to our hips) our feet should fall is while watching "Running the Sahara".  In this documentary, the elite, amazing runners complained that in running in the desert, they would frequently have to run in the tire track of the support vehicle.  That meant their feet would follow a narrow line and that was contrary to their normal running style.  That comment rang in my head while i'd run i'd purposely "straddle" sidewalk seams to ensure my feet landed below the hip sockets from whence they sprout.   

I know my efforts in a slightly wider landing led to my 5km PR - there are indisputable torsional benefits gained by not crossing over. 

Walk on a piece of string or along a seam in the concrete or walk on the lane dividing lines on your local high school or college track. What happens ? If you walk on a single line you will find yourself more unstable as compared to walking with a foot fall directly under your hips and knees the way it is supposed to occur. The limbs are a pendulum and economy and biomechanical efficiency as well as injury reduction will occur when the parts operate in the most effective manner.
We have all of our cross over runners, as you see her doing in the first half of this video before she corrects to anti-cross over (ie. natural), first walk on a line. In our case we use the metal drainage grate outside our office that you see in the video for just that purpose, they walk the grate. Then they run the grate. We ask them to feel ....... want to read the rest ? head over to our blog here for the entire article.

http://thegaitguys.tumblr.com/post/29486393822/the-cross-over-running-techniq...


Here are the other related cross over links here on youtube:
Part 1: http://youtu.be/LG-xLi2m5Rc
Part 2: http://youtu.be/WptxNrj2gCo
Part 3: http://youtu.be/oJ6ewQ8YUAA

^^Thanks Gait Guys for articulating what I had to learn the hard way :)

Transitioning To Minimal Shoes (The How?)

I found I needed to type this story a few times in a row today while giving advice to other runners.  

Do I just take out my orthodics or 'just' buy Vibram Five Fingers and take off running??

After 1.5 years I can run a competitive distance race with NO shoes. Although that may not be a goal of yours, it's an indicator of foot strength.  As a kid I had such flat feet that the outside and inside of my feet looked the same. Now I have a strong-looking raised arch. It's a wonderful thing but it took a loooong time. I'm not sure I took the most direct path to achieve this. 

There are two approaches here and one will better suit your race-schedule, fitness goals, ability to be patient, etc.  There's two ways to approach your goal of building foot strength.

1.) Keep your current running (or training) schedule with minor alterations and wean yourself slowly off inserts, raised heels and cushioning over time.  Example: Going  from a 10mm raised heel shoe to a 4mm, to a 0mm.

 --The downside of this technique is that you have no real motivation to fix your form/balance.  One may develop some intermediate issues - such as, it's hard to have a fast cadence when your heel is raised, it's hard to know you're mid-footing landing when you have ~0.5" of cushioning.

Or

2.) BAM, press reset and run (or train) ONLY 5 MINS barefoot twice a week for a month, and increase frequency slowly. then add a zero-cushioned protective shoe (like Altra Adams, Merrell Trail Gloves, Vibram Five Fingers, BF Inov-8s etc.) when barefoot, only run on hard smooth debris-free surfaces. concrete or asphalt will give you indicators that you're doing something wrong (like over-striding-aka heel-striking, or pushing off too much)- either of which would cause hotspots on the soles of your feet.

 --The downside of this technique is that you may affect your current fitness level.  BUT this is easily overcome by substituting your previous intense running sessions with rowing, swimming, cycling to keep the engine strong.  The unshod running will build foot/leg muscles that have been asleep since your first heavy toddler shoes.   

More info on shoe selection for Running and Crossfitting 

Absorption - Why is Energy Return a Bad Thing?

If all is sequenced well, and if proper form is used, running is partially muscle (work) and elasticity (energy return). Both of which your natural human form is more than capable of; in fact, your body is built for these functions. Contrary to popular shoe-salespeoples' (and some doctors') beliefs, cushioning in your running shoe alters your running stride in a negative way: by limiting the natural elasticity in your running stride. Let's look at the mechanics.

When we land on the ground during our foot strike our muscles tighten and springy tendons lengthen.  Our weight is absorbed by springs in the feet and legs. If we hold that muscular tension until it's time to lift that foot back up, we get to take advantage of the spring tension of those tendons.  The stored energy in those springs act like a helping hand - a little springy assist to get us into our next stride.  

Seems like a system designed pretty well. So how do we mess it up? Think about it this way: If you sprung that spring tension prematurely then you'd have to use ALL muscle to get you into your next stride.  That's how we mess it up: by springing the tension early with well-cushioned footwear.  Cushioning absorbs the stored spring energy and you don't get the assist you would normally. 

Here's a visual that reinforces the point: Imagine you're bouncing a basket ball.  The stored elastic energy gets the ball 80% of the way up to your hand.  The other 20% comes from you using downward muscular force.  Think about how hard you have to push that basketball so it will return to your hand, dribbling down the court.  Now think about how hard you'd have to bounce the ball if it were on a softer surface, like a gymnastics mat.  A thick mat, like a gymnastics mat, functions as a cushion that will absorb a great deal of that stored spring energy. The stored energy is not returned to the ball.  To get the ball back up to your hand you have to push hard enough to make up for the loss in the ball AND the mat.  The springiness of the gymnastics mat (or any other cushioning-type surface) is horrible for energy return.

No surface is as good as the hard floor in returning the stored elastic energy in the ball. 

Similarly, no spring constant (in the form of cushioning) in a shoe will help the runner get that energy back.  The runner's muscles have to make up that work. 

Save your energy for running, not cushioning and see your speed and efficiency improve and your injury rate decrease (provided you use natural form).

Tip:

Note we have to "hold that muscular tension" - seems like a lot of work, right?  To reduce how long muscles are engaged while you run: speed up your cadence! Remember: Shock absorbed by springiness in your body is returned again in your next stride.