INTRODUCTION
“Core Stability” is defined as the ability to control the position and motion of the trunk over the pelvis in order to attain optimum production and transfer of force and motion to the athlete’s terminal segments in all integrated athletic activities (6). Wow! No wonder we all focus on core strength and coordination with our high-level athletes. However, can you say you focus on or at least perform a breathing screen with every athlete before diving into high-level core stability and coordination? If not you are missing a huge part of the core stability screening and training for athletic optimization. If you overlook these possible breathing and core activation faults the athlete may never gain the best core stability to optimize their throwing, running, and kicking, which can lead to increased risks for peripheral tissue injuries.
With high-level athletics, every bit of energy transfer makes a difference in performance and the body uses the core to transmit this energy. All of these purposeful athletic movements must start with the feed-forward proximal stability mechanism in order to transmit force across the whole body. If this force cannot be transmitted up the chain, and the same speed and velocity of sport’s motion is to be maintained, then the small peripheral joints must work harder to make up for the lost kinetic force. Thus, athletes need correct respiratory function and core stability for efficient biomechanical, sport specific function, in order to maximize force generation and minimize joint loads (6).
Respiratory/ Core Evidence Based Connections
So how does breathing function with core stability? Simply put, if you cannot breath properly you cannot brace properly. Breathing and core stability go hand in hand, as the majority of the respiratory muscles work synergistically with the core muscles or even function as both. The diaphragm and pelvic floor have been postulated to be major contributing muscles in order to attain true trunk stability by helping to increase the pressure in the abdominal cavity, otherwise known as “intra-abdominal pressure” (5). Thus the forgotten precursor to abdominal bracing and true core stability is a comprehensive, static anthropomorphic and dynamic breathing assessment, with a trunk feed-forward activation assessment prior to high-level training.
Respiratory and core muscles are most important for what can be referred to as feed-forward, subconscious, automatic stabilization. Athletes need to be able to attain this trunk control and core stability with optimized breathing patterns under stress and fatigue. This is not always inherent in every athlete, but is pivotal in order to provide stability prior to and during all motions. A simple concept to remember is: proximal stability before and during distal mobility (12). Another component to reducing peripheral tissue injury is reducing the time-to and time-under fatigue. This is through optimal systemic oxygen input to the body, which requires efficient energy transfer through core stability. When an athletes supply of oxygen, via the respiratory system or passive force transmission via core stability fail, the athlete will rely more on their peripheral tissues and joints in order to compensate for loss of whole body kinetic force transmission. Which has been shown to increase peripheral tissue fatigue, reduced proprioception, and increase incidence of tissue injury (13). This is mainly due to the fact that with fatigue we see a decrease in position sense/ proprioception of sport-specific central and peripheral joints leading to increased tissue overload. It was shown in 2003 and 2007 that throwing athletes had decreased upper extremity proprioception at the onset of and during throwing under fatigue (9,13). This study and many others have supported Janda’s theory that fatigue is due to a reduction in the feedback from the muscle spindle, which then affects proprioception and posture (12). It can also be postulated that not only peripheral but also central joints have improved stability due to appropriate proprioceptive function and feed-forward control (12). Regional interdependence is a theory that states that seemingly unrelated impairments in remote anatomical regions of the body may contribute to and be associated with a patient’s primary report of symptoms. In this case, poor trunk motor coordination and timing can lead to peripheral or central joint/ tissue overuse and injury (15).
Respiratory/ Core Evidence Based Anatomy and Training
The core musculature is responsible for the preservation of spine and pelvis stability, which aid in the generation and transfer of energy or force from the trunk to distal segments during movements (6). These muscles can include the scalenes, deep neck flexors, sternocleidomastoid, pectorals, intercostals, diaphragm, rectus abdominis, transverse abdominis, internal and external oblique, lumbar paraspinal muscles, and pelvic floor muscles. Athletes also need thoracic static structures to be in optimal positioning in order to create an environment for respiration and core musculature to work most efficiently.
So which should we focus on first? Well breathing of course! You cannot brace or play any sport with perfection if you cannot breath, and the athlete’s need to attain the best breathing posture will supersede the best posture for stability if they are not trained to work together. Ideal posture or positioning for core stability will be compromised in order to put the body into a position to optimize breathing and maintain respiration, as the body will always choose oxygen and respiratory function over stability and trunk control. (12). Clearly this can come at a large price if you are out of breath, unstable, and are about to be hit by a 300 lb linebacker in the NFL. Studies have shown time and time again that these muscles cannot, and should not, solely be trained to work in isolation. The transversus abdominis muscle is only able to produce 1-2% MVC in isolation before the aid of the internal oblique, pelvic floor, and the other trunk muscles are activated (10/11). The diaphragm and transversus abdominis muscles in healthy adults both fire synergistically prior to isolated lower extremity, upper extremity and trunk movements in order to stabilize the trunk independent of the breathing cycle phases (4/5). Therefore, in order to activate the optimum trunk musculature we must focus on feed-forward core bracing with correct breathing patterns which will be ultimately trained under fatigue.
So now we see that the core muscles should be trained in synergy with breathing and can’t be isolated, we can move onto the thought of absolute core muscle strength. Throughout the article I have talked about the importance of this feed-forward, subconscious, automatic stabilization in order to stabilize the body for limb motion and in order to transmit kinetic forces. I focus on the timing of these muscles and activation patterns because of the previous studies stated and the fact that it has been shown that we only need up to 10% MVIC of the trunk muscles in order to provide joint stiffness in lumbar spine for integrated full body movements (2/10/11). Also, even if you think the only way to gain core stability is through strength; you should know that it has been shown that instability at a joint may still be present with normal strength measurements (3). Since we don't need much absolute strength for increased stability or force transmission, and even with absolute strength joints can show instability, it seems that evidence is pushing towards core faults being mostly coordination faults rather than absolute muscle power faults. Therefore, we should focus our efforts on breathing, endurance, timing, and feed-forward autonomic core activation, with progression to sport specific difficulty in order to attain true useful trunk stiffness and functional athletic stability.
Respiratory Objective Exam
There are many different ways to perform an objective exam to assess respiration and they can be tailored to the individual athlete you are evaluating. I will discuss one method that I prefer for a comprehensive respiratory and core activation evaluation. Take note that this is a supine examination; therefore standing posture, movement, strength, and coordination examinations should supplement the exam that I will describe below.
In the supine position, with the athlete relaxed, have both legs flat or both knees bent and feet flat (hook-lying) on the table, and visually examine the athletes static/ dynamic anthropomorphic structures with subconscious tidal breathing. Take note of the chin neck angle, as this can cue you into which muscles/ joints are being over or underutilized and will cue you into the athletes preferred cervicothoracic positioning. Visually evaluate the cervical musculature and the tracheal position. Visually examine the asymmetries of the sternum, clavicles, ribs, and pelvic tilt. Notice any scarring, increased and decreased muscle tone and bulk, especially in the lateral obliques, as they may be a site of decreased trunk stability. Observe for thoracic cage deformities such as pectus excavatum/ carinatum, scoliosis, excessive kyphosis, and any other deformities or irregularities picked up from other examination procedures in this position. The anteroposterior chest diameter should be less than the transverse diameter. The normative ratio of AP to transverse diameter is about 0.70 to 0.75 in adults, which increases with age (14). These static structures are the foundation, which the core and respiratory muscles have to work from, and it can greatly affect their ability to stabilize and transmit force throughout the body. After the visual static structure assessment has taken place, watch the athlete’s preferred subconscious breathing pattern at tidal volume, taking special note of abdominal/diaphragmatic filling and rise as it relates to chest rise. Reassess with the athlete taking a couple full inspiratory breaths as well. Ideally we want to see less chest compared to diaphragmatic rise. Rise in terms of where the body chooses to move from with resting tidal and full inspiration breathing. This is important because if the athlete is relying on anterior-posterior chest expansion over diaphragmatic expansion in order to breath then this may lead to increased motion at the lumbo-throacic junction which can lead to increased spine and tissue stress, especially in times of fatigue.
Next, if needed, place one hand on the chest and one on the abdomen of the athlete just below the costal angle. This will further help you to assess the motion of diaphragm and chest as the athlete breaths at tidal and full inspiratory volume. Place your thumbs tip to tip at the xiphoid process with your other fingers and palms lying flat on the ribs facing towards the athlete’s shoulders in the intercostal spaces to feel for any rib expansion abnormalities and in order to estimate the costal angle. The normal values of this angle is 90-110 degrees. This angle is important because it will give you insight into which muscles may be inhibited or hypertonic, as well as see if the athlete has any set anthropomorphic abnormalities of the rib cage, and/or thoracic spine. Remember, rib angles as well as the costal angle are a direct reflection of the thoracic spine orientation, and it most certainly is appropriate to evaluate the thoracic spine if you feel this is the structure of anatomical variance.
A palpatory exam is also an important part of a full respiratory and trunk control exam. Palpate all quadrants of the abdominals to feel for increased or decreased muscle tension or any tissues with increased sensitivity. You have already assessed active rib mobility with breathing, but it may also be important to further assess passive rib mobility by placing your hands flush against the ribs on the anterior thorax with the addition of broad overpressure. Ask yourself these questions; Are they starting the breathing motion correctly or are they stuck in an expiratory rib/ thorax position possibly categorized by a narrower than 90 degrees costal angle with more vertically positioned ribs? One theory is that this could be due to or lead to increased external oblique or rectus abdominis resting tension and reduced internal oblique activation or resting tension. Are they starting the breathing motion correctly or are they stuck in an inspiratory position categorized by a wider than 120 degrees costal angle with more horizontally positioned ribs? One theory is that this could be due to or lead to increased internal oblique activation and reduced external oblique resting tension. Lastly, is the athlete asymmetrical with one side of his or her ribcage flared up and out or held down and the other working within normal limits? As a grossly simplified muscular guide, the internal oblique will most likely increase the rib angle (ribs appear more horizontal) and costal angle and can pull the ribs in an anterior to posterior direction as well as in an inferior and lateral direction. Or conversely they could cause a slight anterior pelvic tilt due to its line of pull. The external oblique will most likely decrease the rib angle (rib appears more vertical) and costal angle and can pull the ribs in an anterior to posterior direction as well as an inferior and medial direction or conversely could cause a slight posterior pelvic tilt due to its line of pull. Whereas the rectus abdominis will pull the two sides of the rib cage slightly medially and inferiorly decreasing the costal angle or conversely could cause a slight posterior pelvic tilt due to its line of pull. There are numerous ways to treat these findings and many different continuing education classes that one could take in order to affect the athlete’s faults as comprehensively as possible. However, explaining all of the ways to treat these findings is out of the scope of this article, so do what you know and see if you can make a change. Having said that, any faults and abnormalities picked up with the visual and tactile breathing assessment should be assessed further and should be normalized with soft tissue, joint mobility, or coordination treatment via tactile, verbal, and visual cueing until the patient can correct the abnormalities with tidal breathing and maximum inspiration or until they are as minimal as possible.
Core Activation Objective Exam
Next up is the core activation objective assessment. Place your thumb of each hand on left and right inferior lateral quadrants of the athlete, just medial and superior to the ASIS. At the same time place your middle finger or pinky finger on the athlete’s posterior lateral trunk, superior to the posterior iliac crest, and at the same vertebral level as you thumbs (Pincer grip). In the respiratory assessment you felt AP motion of the thorax and with this new grip you now have your hands in a great position to feel for lateral, anterior and posterior abdominal wall filling. Next, with you hands in this position have the athlete breath with normal tidal volume and with maximal inspiration, feeling for the filling of all four palpated cavities at the same rate and depth. The timing and fullness of all quadrants should be the same, as we want the athlete to fill their cavity equally and cylindrically in order to achieve the optimal intraabdominal pressure and core stability. If they cannot do this, then your work starts here. Again these faults should be normalized with soft tissue, joint, or coordination training via tactile, verbal, and visual cueing until the patient can correct the abnormalities or until they are as minimal as possible.
Next, with the athlete lying in supine, lift their legs into a 90/90 position, supporting their full lower extremity weight onto your thigh with your foot on the table. Another possible option for overhead athletes would be to lift both of their arms overhead (to 140 degrees of shoulder flexion) with their wrists supported on your thigh. Next, verbally cue the athlete to slightly lift their arms or legs off of your passive support until they accept the full weight of their limbs. You want the athlete to lift their own arms or legs off of your support as opposed to you pulling your passive support away from them, as this will most closely simulate their automatic preferred abdominal activation pattern. During this phase of testing observe their core for their timing and quality of their preferred automatic motor activation as they start to support the weight of their legs or arms. Look and then feel (using pincer grip) the abdominal cavity as a whole, as we want to see symmetrical cylindrical filling just prior to limb motion. This would show optimal proximal stability before voluntary limb muscle activation and motion. Observe the navel for any motion, as this can be an obvious cue into trunk muscle activity. If all of the core muscles are working in synergy the navel should have very little to no movement. If you see navel motion as they accept the distal weight, this will cue you into areas of increased muscle pull and activation or decreased pull and activation as the navel is pulled towards the direction of dominant muscles and away from non-dominant muscles. Look and then feel for cues of an overactive rectus abdominis, which can be seen with increased abdominal rise anteriorly, greater than lateral abdominal wall filling. Ideally you would want to see and feel cylindrical core activation, which is equal and symmetrical in timing, pressure, and filling just prior to active limb motion. This should be done without any external cueing, as this would show that the athlete has automatic feed forward core stability in preparation for limb motion and mobility.
At this point in the core activation evaluation it is important that you try to see if they can change their pattern towards optimal with minimal cues. You can be as creative as you like, but try to get the patient to understand what normal is and why it is important, and then have them strive to achieve that with minimal cueing. Tactile cues for abdominal filling may be as simple as having the athlete breath into the area where there is decreased absolute filling or decreased rate of filling. You can facilitate this via your tactile pincer grip pressure, having them focus on the pressure of the table, or their own tactile pressure via self-pincer grip. You can manually push down and set the ribs in the correct position and then see if the patient can breathe while actively holding that corrected rib positioning with their core muscles. Can they then progress to deep breathing while filling all cavities symmetrically with that corrected positioning held. Finally can they support their lower and upper extremity weight and then move their lower extremities in the supine position while actively holding their ribs in that corrected position with proper breathing. Verbal cues can be simple and can include “breath into this part”, “fill/ firm this part of your stomach/ back” in order to attain proper breath/core muscle filling. One of the best verbal muscle activation cues shown to increase bracing in current literature is “Stop your urine flow” (8). Your athlete may think this is elementary training, but then at that point I usually just say some version of “Your right, this is such minimal motion, and your even lying on your back. But you can not even lay here and hold the weight of or move your legs with proper core activation for stability, support, and power, what makes you think you can sprint, hit, or jump with correct core activation and stability in order to optimize your movement and prevent injury?” it usually drives home the point that they already expressed, which is that this training is so simple compared to usual higher level athletic integrated motion or weight training and you have just showed them that they can’t do it correctly.
This entire assessment will allow you to see if the abnormalities found can be changed or trained in order to attain the optimal thorax positioning for maximally effective automatic feed-forward abdominal bracing with limb motion and correct deep breathing. If you have now assessed your athlete and found that they are able to correctly breath and brace with lower or upper extremity motion then the next step is higher level trunk muscle testing and strengthening in order to maximize the athletes full core stability potential (which will be the focus of my next article). Be creative, as I have only given you one version of possible testing, otherwise you would be reading a large book on this topic not a small concise post. Evidence is always changing and there is always more ways to address each fault found with each athlete. So get out there and build truly effective athletes.
Breathing/ Bracing Quick Sheet
Visual:
Anthropomorphic: chin neck angle/ trachea/ clavicle/ sternum/ costal angle/ ribs/ pelvis
Soft Tissue: anterior cervical musculature/ 4 quadrants/ navel position / scars/ muscle tone
Diaphragm vs chest rise: 2:1 or 3:1 ratio
Costal angle: 90-110 degrees
Ratio of AP to transverse rib diameter = 0.70 to 0.75 in adults
Check all with tidal and deep breathing
Palpation:
Diaphragm vs chest rise 2:1 or 3:1 ratio
Costal angle 90-110 degrees
Rib angles
All abdominal quadrants for muscle tone and increased sensitivity
Lower abdominal, anterior and lateral wall filling with tidal and deep breathing for timing and absolute volume with pincer grip
Muscle Actions:
Internal oblique: Increase the rib angle (rib appears more horizontal) / costal angle, can pull the ribs in an anterior to posterior direction + inferior and lateral direction or slight anterior pelvic tilt due to its line of pull.
The External oblique: Decrease the rib angle (rib appears more vertical) / costal angle, can pull the ribs in an anterior to posterior direction + inferior and medial direction or slight posterior pelvic tilt due to its line of pull.
Rectus abdominis: Pull the ribs medially and inferiorly or slight posterior pelvic tilt due to its line of pull.
Bracing Activation Cues:
Verbal: “Stop Your Urine Flow”, “Think of filling the lateral abdominal/ posterior wall”, “breath into the tactile cue”, “blow out forcefully”
Tactile: PT pincer grip, PT hands on chest and diaphragm, Athlete to feel table under the body, Athlete’s own hand on chest and diaphragm or on abdominals with pincer grip, manual joint and muscle techniques, blocking rib or joint motion with deep breathing, using muscles to hold ribs in the proper position
Visual: Athlete to watch abdominal rise, Athlete to watch belly button motion in mirror held above by PT; athlete to watch video of correct bracing or see diagrams
Citations
1. Cholewicki J, Juluru K, McGill SM, et al. Intra-abdominal pressure mechanism for stabilizing the lumbar spine. J Biomech 1999; 32 (1): 13-6: 76-87
2. Cholewicki J, Panjabi MM, Khachatryan A. Stabilizing function of trunk exor-extensor muscles around a neutral spine posture. Spine. 1997;22(19):2207–12.
3. Freeman MA, Dean MR, Hanham IW. The etiology and prevention of functional instability of the foot. J Bone Joint Surg Br. 1965;47(4):678–85
4. Hodges PW, Richardson CA. Contraction of the abdominal muscles associated with movement of the lower limb. Phys Ther. 1997;77(2):132-144.
5. Hodges, P W et al. “Contraction of the Human Diaphragm during Rapid Postural Adjustments.” The Journal of Physiology 505.Pt 2 (1997): 539–548. Print.
6. Kibler WB, Press J, Sciascia A. The role of core stability in athletic function. Sports Med 2006; 36(3): 189-98.
7. Kim, Hyun-Dong et al. “Changes in Activation of Abdominal Muscles at Selected Angles During Trunk Exercise by Using Ultrasonography.” Annals of Rehabilitation Medicine 39.6 (2015): 950–956. PMC. Web. 20 Feb. 2018.
8. Lee, Diane D. “The Pelvic Girdle: An Integration of Clinical Expertise and Research”. Churchill Livingstone, Elsevier, 2013.
9. Lee, Hung-Maan et al. Evaluation of shoulder proprioception following muscle fatigue. Clinical Biomechanics , Volume 18 , Issue 9 , 843 – 847. 2003.
10. McGill, Stuart. Low Back Disorders: Evidence-based Prevention and Rehabilitation. Champaign, IL: Human Kinetics, 2002. Print.
11. McGill, Stuart. Ultimate Back Fitness and Performance Fourth Edition .Waterloo, Ontario Canada, 2009. Print.
12. Page, Phillip, et al. Assessment and treatment of muscle imbalance: the Janda approach. Human Kinetics, 2010.
13. Tripp, Brady L, Eric M Yochem, and Timothy L Uhl. “Functional Fatigue and Upper Extremity Sensorimotor System Acuity in Baseball Athletes.” Journal of Athletic Training 42.1 (2007): 90–98. Print.
14. Tuteur PG. Chest Examination. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Boston: Butterworths; 1990. Chapter 46.
15. Wainner RS, Whitman JM, Cleland JA, Flynn TW. Regional interdependence: a musculoskeletal examination model whose time has come. J Orthop Sports Phys Ther. 2007; 37(11):658–60
