The Biomechanics of Running and its Transfer to the Performance of CrossFit Exercises

Posted: June 12, 2013 in Uncategorized

 

running-poserunning-pose

Perhaps the biggest criticism of CrossFit, whether merited or not, is that CrossFit training is dangerous, and high-risk. I regularly hear things like “it’s not a matter of ‘if’ but rather of ‘when’ you will be injured.” Before starting myself, I may have believed these types of comments. In fact, recently there was a “study” done by NSCA about the efficacy of CrossFit training. The study demonstrated that CrossFit training increase fitness throughout many domains, but also mentioned that a significant number of participants failed to complete the study because of injury; which was later discovered not to be the case. (You can read about it by following this link: http://journal.crossfit.com/2013/05/acsm.tpl) The more I have become involved, the more I realize how over-blown these statements are, and in addition, I believe that many “CrossFit injuries” can be traced to other factors outside of CrossFit’s training methodology. One specific and major factor that I believe plays a role is the movement biomechanics of running and if/how running gait affects the occurrence or risk of injury.

Good CrossFit programs and coaches spend a lot of time training beginners on the skills that CrossFit training demands. Countless hours are spent on form of Olympic lifts, gymnastics movements, double-(and now triple)unders, rowing and many others. All of these skills are important and time should be spent on perfecting them. We regularly see ‘running’ in CrossFit workouts in varying distances from 10 meters to a mile or more, but with very little, if any, time being spent on the skill. Don’t get me wrong, the information is out there. There is a lot of great information on the subject including the POSE method followed and taught by Brian MacKenzie and a lot of other associated information on www.CrossFitEndurance.com/run . The Lord of the Supple Leopard Legion Kelly Starrett, along with MacKenzie, recently talked at length with Dean Karnazes, (Ultra-marathon Man) about running form and function on their pioneering series “Genetic Potential.” (http://www.youtube.com/watch?v=duUo8fRarQ4) There is a great article from the CrossFit Journal from 2008 titled “Form for Runners, from Head to Toe (http://library.crossfit.com/free/pdf/65_08_Runners_Form.pdf). We are seeing many in the CrossFit community embrace running as a skill and while we have a lot of great information on the subject both within and outside the CrossFit community, little time and effort is spent by coaches and members alike on perfecting a skill that I believe will translate performance in many, if not all, other CrossFit skills.

It is not my purpose here to argue CrossFit Endurance vs Conventional training; there is enough of that out there, but if you want to follow one person’s perspective in training that way, you can follow my other blog and personal experience as I use the method to train for a Marathon in the fall at www.mycrossfitenduranceexperiment.wordpress.com . The purpose of this entry is not only to (1) identify proper form, but also to (2) isolate common flaws in running gait, (3) how to correct those flaws, (4)discuss how those flaws might affect the performance and efficiency of other CrossFit skills, and (5) how/if they may increase injury occurrence if not corrected.

To begin, I wish to outline what I believe, and what are becoming, the generally accepted standards of biomechanically efficient running, as well as the factors that have limited or played a role in not applying them earlier.

Many things have contributed to the collective poor running mechanics that can be observed in most runners, let alone crossfitters. The first may be shoes in general. There has been a virtually linear correlation between the occurrence of running injuries and the “advances” in running shoe design over the last 30-40 years. Another is a society designed to make things easier. Sedentary lifestyles of sitting and desk-jobs have led to poor hip and shoulder mobility, tight and overactive hip flexors and chest muscles, and weak/underactive glutes, hamstrings, abs and back. Dress and athletic shoes with raised heels have screwed up the length/tension relationship of the calves. These factors, as well as others have wreaked havoc on the movement system and accelerate the rate of the overuse/chronic injury cycle. Recognizing all that is, and has gone, wrong, the following is an outline of a biomechanically correct and efficient running gait.

1)      Foot Strike: The foot should land softly, underneath a bent knee, on the mid or fore foot. Improper foot strike, specifically with the heel under a straight and locked knee, is the most common, and potentially most dangerous, running error. The easiest way to stop heel striking is to avoid over-striding by shortening the stride and increasing the cadence. (Think about running “quicker” and “quieter”)

2)      Knee Movement: The knee joint is classified as a hinge joint; that is it moves in a single fixed plane of motion. Although it is a single plane joint, there are occasionally varus and valgus forces on knee caused by heredity, and well as lifestyle factors that may have caused the imbalance. At foot strike, the knee should be slightly bent, causing the muscles of the upper leg to work synergistically with the lower leg muscles to eccentrically decelerate the movement. This type of movement minimizes the stress on the knee joint structures that often cause inflammation and pain. If the knee is locked at the point of impact all of the concussive force travels up the lower leg leading to shin splints and/or stress fractures, and continues through the knee structures and can transfer up the kinetic chain into the hips and lower back.

3)      Hip Position and Mobility: I like to think of the hips as a suspension bridge. In order for the suspension bridge to remain flat, the cables holding it need to remain balanced perfectly between being too tight or too loose. If a cable is pulled tight, it is going to carry more tension and stress and will be more likely to break. In addition the bridge will be pulled off of the level plain and other cables become loose, causing a structural imbalance. Our pelvis is the same, and through lifestyle factors many people exhibit some form of a pelvis imbalance to some degree. Very commonly we see anterior pelvic tilt caused from living in a sitting society. As a result of extended sitting, the hip flexors become overactive and tight, pulling the hips forward and ultimately leading to back pain and weakness. Hip imbalances and subsequently injuries, are compounded in individuals who run incorrectly without correcting excessive pelvic tilt.

4)      Core/Torso Stability: The common, and incorrect, running posture that can be observed in many runners typically includes the things mentioned above (ie, heel strike, over-extended knee, anterior pelvic tilt etc) but perhaps the easiest thing to observe is an upright torso. If the torso is upright (perpendicular to the ground) the vertebrae is stacked and the concussive force travels up the spine and can lead to hip, low-back, and nervous pain. By simply leaning forward, and keeping the torso and shoulders in front of the hips, it will carry the momentum forward, force a shortened stride will assist in proper foot strike, and decrease stress on the knees, hips and back. The easiest way to figure out the proper forward lean position is stand upright and lean forward until the point that you have to take a step to prevent you from tipping over; that is your forward lean position.

5)      Arms: There is a great article on arm mechanics here but I will paraphrase it for my article: (http://blog.altrazerodrop.com/ltrchat/adamstpierr/ ). Arm mechanics are sometimes ignored but can play a large role in efficiency and decreasing lower-body injury and imbalance. The most basic “rule of thumb” when it comes to arm mechanics while running is: keep it tight. Much less energy is used if the elbows are bent to 90 degrees or less and kept close to the body moving in the sagittal plane. The straighter the arm, or the larger the swing (especially if the hands cross the body’s midline), the larger the lever, and more energy is needed to control the movement. Another important thing to note is that the angle of the elbow should not change throughout the stride, but should remain a constant angle.

better-running

 Now that we have talked about the most biomechanically efficient way to run, let’s explore if/how running form affects the performance of other CrossFit exercises. Just like above, we will start with the feet and work up, and I am going to focus on three areas that people commonly experience injuries that are related to CrossFit: Achilles tendon/calves, knee and back, but before we talk about the specifics, I want to introduce a concept that plays a role in each of examples I list below.

The difference between walking and running I basically two-fold. Natural walking gait is typically heel strike and roll pattern, and with walking there is always at least one foot in contact with the ground all the time. In jogging and running, the natural and biomechanically efficient gait is fore-foot strike, and only one foot is in contact with the ground at any one time. Running is done at a higher velocity (speed) than walking and as a result creates exponentially more force at foot strike as the foot is required to eccentrically decelerate, stabilize, and concentrically accelerate the movement. This additional force can wreak havoc on the joints of runners who utilize conventional training programs built around long-slow-distance, especially if they heel strike. Now let’s build on that idea as it relates to CrossFit training. One of CrossFit’s training principles is “high-intensity.” When it comes to running, this means that the training is prescribed to be at higher speeds (greater force) for shorter distances. If we take crossfitters without efficient running training and have them run at higher speeds, we are ultimately perpetuating the rate of injuries in ways that are listed below.

Another item that will play a role in all of the examples outlined below is that an upright/ heel strike running posture doesn’t allow for the balanced development of the calves and glutes in balanced ratio to their antagonists creating imbalances and leading to reciprocal inhibition and synergistic dominance that, if go uncorrected, will decrease performance and increase imbalances and injuries.

Ankle:  Mobility and the length/tension relationship of the calves muscles group. Last year in the Crossfit open, one of the workouts included box jumps, and as a result of thousands of people participating, there were several reports of calve and Achilles tendon ruptures and injuries. As a result, we have seen a shift away from box jumps because of fear of injury; and participants in the open this year were allowed to step up and step down as a modification (a modification that proved to enhance performance and improve the scores of many athletes who did it multiple times). I am not going to say that everyone should do full box jumps, but I believe that there are two contributing factors related to poor running mechanics that would significantly decrease the risk of this injury. A heel-strike gait, coupled with shoes that have a raised heel (lifting shoes included), accelerate the problem because the posterior chain is shortened. As a result of the shortened posterior chain, the length/tension relationship of the muscles of the lower leg are not conditioned to prepared for the stress and range of motion demands of an exercise like box jumps. Correct running gait, as outlined above, assists those muscles with the demands of eccentric deceleration loading that is required for the exercise. Having a shortened posterior chain (wearing oly lifting shoes) may be an advantage for lifting, but can be a great disadvantage and lead to injury in other exercises.

Knee: Occasionally in CrossFit we see knee problems arise, but more often than not they are associated with, or caused by, some other force entirely. One such factor may be heel-strike running. As mentioned above the forces associated with running are exponentially greater as speed increased in relationship to walking. That impact travels up the kinetic chain causing problems from the bottom up. These include shin splints, stress fractures, soft tissue overuse injuries of muscle and tendon units, Joint pain and inflammation at the knee, hip and back. The faster the heel-strike gait speed, the greater the impact, and further up the kinetic chain the impact travels. The impact of a heel-strike does not allow the muscles of the leg to softly transition between strides, but instead the muscles are forced to stabilize a violent impact that reverberates up the kinetic chain. That added impact can damage shock absorbing structures like the meniscus of the knee. If someone has meniscus-related injuries or are lacking cartilage in their knee due to improper running mechanics; or if they have chronic low-back pain and anterior pelvic tilt because they run upright, it will make it painful and nearly impossible to squat, lunge and jump as prescribed in CrossFit WODs, and as a result, their progress will be limited to the degree in which they can’t perform the exercises.

Back: The back is probably the area of that we most hear about injuries as they pertain to CrossFit. While poor running posture and gait are probably not the leading contributor to back weakness and injury, it does play a role that can make or break the back (no pun intended) strength. The lower back (specifically the SI joint and the surrounding structures) are often the subject of CrossFit-related back pain. Heel-strike running has been shown in studies to accelerate degenerative back disorders and increase the occurrence of low-back pain. In addition to the additional shock, upright runners displayed lower levels of low-back muscle mass, strength and stability. When you take those variables into consideration, adding a regimen of weight-lifting may compound the problem and increase the occurrence of low-back injury. As mentioned about upright and heel-strike runners have underdeveloped glutes in relationship to the hip flexors. Tight and overactive hip flexors anteriorly rotate the pelvis forward increasing low back pain and the chance of injury, especially when weight is added. There are also significant and observable upper-back issues to be discussed. An upright runner’s shoulders are directly above the body’s center of mass, decreasing the need for the muscles of the upper back to stabilize the shoulder girdle. This type of running weakens those muscle and lead to a rounding of the upper-back and shoulders. Those who run with their shoulders and chest in front of the hips must engage the muscles of the upper-back to stabilize the body from falling forward. This will assist during lifts like the deadlift, power clean, snatch etc.

Conclusion: Running efficiency and economy may not be greatest factor or contributor to injury in CrossFit, but it is a skill and should be looked at as such. All skills should be regularly coached and critiqued, and special instruction should be provided for those skills that transfer to others, especially when performance can be enhanced and injury decreased. In order to get your running legs up to speed you need to train your body to utilize proper biomechanics and emphasize the overall movement from the hips. All power activities rely on producing power from the hip (ie. Glutes, quads, adductors, abductors, and hip flexor/extensor groups) in the form of the triple- extension. The triple extension involves the three major joints the hip, knee and ankle which transfer force from a flexed position to an extended position. Now just think about this transferred into your running mechanics. The more powerful your triple-extension the more force you can effectively transfer into the ground and the faster you will move.  Therefore running and CrossFit lifts and exercise transfer directly to each other. At the very least, running deserves more coaching then simply “run 400 meters.”

References:

1)      http://www.thebodymechanic.ca/2011/03/19/barefoot-forefoot-strike-and-heel-strike-a-biomechanics-summary/

2)      http://demotu.org/pralados60/files/2011/05/DuganPMRCNA05running.pdf

3)      http://blog.nasm.org/fitness/running-shoe-or-minimalist-shoe/

4)      http://cptsmashfitness.com/bodyfat-loss-basics/ranger-pt-shorts-make-you-run-better/

5)      http://www.elitetrack.com/article_files/biomechanicsofrunning.pdf

6)      http://www.sfecrossfit.com/resources/articles/crossfit-and-running-shoes/

7)      http://www.altrazerodrop.com/webapp/wcs/stores/servlet/StaticContentView?langId=-1&storeId=15151&catalogId=18952&pageTitle=Learn+To+Run&pageName=LearnToRun

8)      http://blog.altrazerodrop.com/ltrchat/adamstpierr/

9)      http://www.crossfitintrepid.com/2012/10/02/how-walking-gait-differs-from-running-gait/

10)   http://blog.evidencebasedfitnessacademy.com/2011/01/23/synergistic-dominance–low-back-pain.aspx

11)   http://library.crossfit.com/free/pdf/64_07_PoseRun_Techniques.pdf

12)   http://www.bettermovement.org/2013/barefoot-running-squatting-like-a-baby-and-pygmy-feet/

13)   http://home.trainingpeaks.com/articles/running/ground-contact-time-and-running-performance.aspx

14)   http://woman.thenest.com/forces-hip-midfoot-vs-heel-strike-running-gaits-14361.html

15)   http://www.runnersworld.com/running-tips/footstrike-and-its-possible-effect-lower-back-pain

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