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May

Does posture influence running biomechanics?

Practitioners who work with running injuries will attest the commonality of their patients’ “weak glutes” being a (major) contributing factor to their injury and / or poor running performance.  Often these very patients are prescribed “glute strengthening exercises” of which they will perform with vigour and excitement in anticipation that this will solve their running ills and get them back on the road to running bliss. Unfortunately, it is common practice to follow such a common approach to this common problem. If only it were so simple! Why then do the waiting rooms of modern sports medicine practices continue to be plagued with these “weak-gluted” humans? Is it inevitable that our gluteal muscles are so prone to failure? Or are we missing something?

Researchers have identified that the structure and organisation of the human gluteal muscle complex (and in particular the gluteus maximus or Gmax), as compared to other mammals was particularly necessary for the evolution of human (bipedal) endurance running capacities (and many moons ago, ultimately for survival). This was concluded through several EMG studies that identified a prominent characteristic of GMax activity during locomotion is how the basic pattern and magnitude of GMax contractions differ substantially between walking and running. During walking the gluteal muscles contract at a very low level amplitude following foot strike and throughout the ipsilateral stance phase with no obvious spike in energy. During running the gluteals tend to contract biphasically with an exceptional “peak” of activity on foot strike and a 2ndspike of activity during foot strike on the contralateral side. The intensity and rate of contraction increases with running speed suggesting GMax activity in particular is dependent on gait speed.

GMax also plays a significant role in trunk stabilisation (relative to gravity), particularly in trunk flexion (forward leaning). The timing of GMax activity in relation to trunk stability correlates with differences in the timing of trunk flexion in walking (after mid stance) and in running during the entire gait cycle. In summary the gluteal muscle complex has an array of important jobs to perform in dynamic movement. However static posture may be a different story. Again EMG studies found that gluteal activity and yes, GMax in particular is supressed in walking and virtually non-existent in standing. Not only does this highlight the specifity of the activities (including climbing, standing from squatting, uphill walking and stair climbing) which require GMax involvement, it can be suggested that unless we are running (or climbing etc) each day we are essentially not needing to use our gluteals for much. This is an important point that may lead to a better understanding of the “weak gluteal syndrome” experienced by so many. More importantly such consideration may improve our exercise prescription for the rehabilitation and conditioning of our runners.

It is necessary to first reflect on principals in motor control and skill acquisition, and consider running from the “beginning”, where the process starts within the human. The human body moves due to the motor programs (google maps of movement) that exist within the confines of the vast neural library inside our skull. Our basic / innate movement patterns exist here and form our habitual movement strategies. All new tasks are organised (according to existing motor programs) considered, learned, correlated, executed and stored for future use. Initially the motor program for running emerges from our primitive brain. Somewhere between innate drive and conscious learning the motor “product” takes shape; the brain builds it’s motor template for running and files away all of the necessary components and information. How running is executed is based on physical and physiological capability, existing habitual movement patterns, experience, interest and practice. Additions and alterations to an individual’s running template occur relative to the time spent engaging in the practiceof running and any consciousattempts to “change” parts of our running biomechanics (as running is executed under unconscious control).

The beauty of the human organism is it’s ability to adapt. As a consequence of physical (and other types of) stress, experience and practice the organism changes. This is what a biodynamic metabolic creature does. In fact, each “stressor” influences an organism’s response to subsequent stressors (a conversation for another time). This adaptation is the whole reason we train. However, humans are great at compartmentalising concepts and therefore assume training is the only (real) place adaptation occurs. We negate the importance of the adaptations which are occurring constantly. It is why we decondition when we cease or reduce training. Consider obesity. It occurs over time due to the stressors encountered by the organism, and the eventual product is excessive body fat and poor hormonal regulation (simply put). It’s an adaptation process albeit a less than desirable one.

Our adaptation is never consistent although training helps create consistency. Even so our training programs must be appropriately progressive to ensure suitable adaptation effects. Therefore, it seems apt to consider how the time spent not training / moving, and for the purpose of this article, not running, may be effecting our running “product”. The point here is the human race as a whole is more sedentary than ever, far more so than previous generations. The decline in our overall physical activity has been happening for several decades and starts from a young age. We sit our children down to “learn” while supressing their physiological and metabolic development. This occurs at a genetic level according to recent Type 2 Diabetes research. Gene expression is literally altered according to the levels of physical activity incurred by an individual. Much of this genetic material is passed on to subsequent generations.

Often this sedentary behaviour continues into adulthood. If less (physical) stress is incurred over time, there is less requirement for robust adaptation (over time). Our brain constructs movement templates based on our sitting and standing posture as we spend many more hours per day here. As such the execution of movement which is essentially a conversation between the brain to the body (neural-kinetic) changes relative to the increased amount of time spent sitting (and standing). It is very feasible our extended sitting behaviour (compared to generations ago) impacts first the neural-kinetic conversation which in turn influences our muscle recruitment patterns, muscle function, fatigability and ultimately movement quality. Simply put the neural-kinetic conversation of a body spending more hours per day in a resting state is going to be very different to the neural-kinetic conversation of a body spending several hours per day incurring increased physical loading.

Here is a simple test to try. Stand side on to a mirror. Observe your standing posture. Close your eyes and feel the weight of your body mass through your feet. Is it through your heels? It is highly likely that a greater percentage of readers will stand in an “arc” formation: leaning back (weight through heels), locked knees, pelvis pushed forward and torso angled backwards relative to the pelvis (A). Take a few steps (walking). Now stand as close to aligned as possible (B); get your ear in line with your shoulder joint in line with your hip joint in line with your mid outside knee in line with you outside ankle joint. Poke yourself in the abdominals. They should feel slightly more firm. Now take a few steps forward. What happens to your stride in walking. Attempt to jog a few strides in the posture.

If posture “B” was done correctly the reader would have noticed that they took a shorter stride in walking and jogging. This is because there is no reason to elongate the stride. In posture “A” we are essentially leaning backwards and therefore are likely to take an exaggerated first (and subsequent) step(s). Therefore our upper body is effectively behind our lower body in forward movement in which case the quadriceps muscles are recruited to “pull” us forward through space. This is because the swing leg is in front of the mid line of the body for an extended period of time (repeatedly). As an adaptive process, we become “quad dominant” due to our repeated and extended time spent in hip flexion (leg in front of the mid line = quadricep) relative to hip extension (leg behind the mid line = gluteals / hamstings). Also, in posture “A” we are essentially leaning backwards from the get go and therefore are increasing the load on the lower back muscles and decreasing the need for gluteal engagement (as we are in trunk extension).

If we change to a standing posture closer to “B” with our torso directly over our pelvis / feet and our entire trunk at the mid line or ever so slightly forward of the mid line it does not make sense to take the exaggerated step (it will feel very strange). As such our upper body stays relatively “in line” with our lower body; our centre of mass (COM = abdominal region) moves over our base support (BOS = standing leg) sooner essentially causing hip extension earlier. Therefore the gluteals engage sooner and for longer. Also, as our trunk is at the midline or slightly forward (in forward flexion) there is increased need for gluteal activity.

I commonly observe in my running patients (of all standards) the propensity to heel strike, often prominently. In doing so their COM is well behind their strike foot on contact (“in the back seat”) and stays here for quite some time in running terms. This costs a runner in both time and energy to transfer their upper body mass from the “back seat” to – “over the foot”  – to “ forward propulsion”. By definition this is considered “over-striding” and utilises the very strong quadriceps group to “pull” us forward over our foot. This can be assumed as the runner’s hip on the strike leg is in deep flexion which is where the quads work best. While the glutes can work to control (slow down) hip flexion the gluteal musculature will not “fire up” properly until the runner’s torso has become aligned with the body and the hip / lower limb goes into extension. The lack of gluteal engagement (early) is exacerbated by an often “sway back” posture where the runner is leading with their chest and / or leaning slightly backwards. This process, repeated over and over and for many kilometres may highlight why our gluteals are “failing” us. Perhaps it is something of an adaptive process. And simply doing gluteal bridges and the like is unlikely to have any impact on the gluteal action in running. It’s a very different task. Yes, gluteal strengthcan be improved doing such exercises.

While this is admittedly a simplistic view of why our gluteals are behaving badly it is one that certainly requires further attention and investigation. It is extremely important to consider the whole picture when addressing a runner’s training needs. Running gait retraining married with functional strength work and a progressive run program is ideal. Capitalising on opportunities to stand with appropriate posture (as a basis for good quality movement), and decrease overall sitting / sedentary behaviour is also clearly necessary.

An insightful biomechanist from yesteryear suggested that posture should not be considered to be the “upright, well balanced stance in an erect position against the forces of gravity, but rather the position(s) the body assumes in preparation for it’s next movement”, thus highlighting the relationship between “posture” and mobility. Posture is the platform for movement quality. The primary function of the “motor system” is to produce motion. Therefore it is makes sense to consider not what is the best “posture” but what is the best “movement patterns” for humans, starting with good standing  and walking posture. After all humans, like all living creatures are designed to move well and a lot.

Learn more about Rebecca Bryce by visiting http://www.opsmc.com.au/person/rebecca-bryce/