into the core

Core training and how it builds our strength & performance

By Iris Saar, Ms. C. Exercise Science candidate, Concordia university of Chicago

The core region of the musculoskeletal system consists of global (superficial) and local (deep) muscles (table 1). Global muscles are regarded as prime movers due to their greater ability to produce force (in terms of torque) as well as distal impact on the extremities, while the distance between the origin and insertion of the local core muscles is smaller, resulting in a more proximal bio mechanical impact (Wirth et al., 2017). The internal obliques are an example of local muscles where the rectus abdominis is a global core muscle (Biel & Dorn, 2006).



Aside from its contribution to movement and force generation, the core acts as a stabilizer, continually ensuring postural control is achieved in relation to the center of gravity (CoG) (Szafraniec et al., 2018). Its location as a central point to the upper and lower extremities, as well as the lower pelvic hip complex (LPHC) is a strategic point of the core, in terms of its impact when stabilization is impaired or not achieved due to partial weakness of the musculature. Postural control is a product of core stability, a multi-systematic process which involves elements of strength, endurance, proprioception and neuromuscular control (De Blaiser et al., 2018). Indeed, deficiencies in postural control related to core weakness may pose risk factors to various injuries; movement compensations arise when a designated core muscles fails to provide enough stability due to relative weakness (Raabe & Chaudhari, 2018). Conversely, improvement in performance may be associated with enhanced core strength when certain training interventions are applied both dynamically and isometrically to the core region (Bayrakdar et al., 2020).


The literature provides a wide base of evidence pertaining to the implications of core training on muscoskeletal stability, strength, injury rates and performance measures; the following paragraphs review the current research and feature three core exercises, together with a respective scientific rationale applied to each exercise.


Core strength and stability

Stability can be viewed as a constantly dynamic trial to reach optimal alignment and equilibrium of the skeleton in relation to the CoG. When stability is partial or impaired, risk for balance-related injuries such as falling increases (Ferraro et al., 2019) as the force coupling capabilities are compromised (Clark & Lucett, 2010). Since stability is correlated and dependent on muscle force, there is a co-dependency between the two variables. One of the measurements to determine posture is sway, which is quantified by the shifting of the center off pressure through vector values (Yamamoto et al., 2015).

Core training exercises can improve strength and stability across the entire kinetic chain. More specifically, exercises that engage the trunk region and surround the musculature from the pelvis through the shoulder girdle, and challenge trunk position relative to the LPHC (Szafraniec et al., 2018). Valuable feedback in researching core stability can be achieved by isolating local core muscles such as the transverse abdominis (TrA); due its more specific role and proximity to the spine, changes in the TrA can affect stability. According to Ferraro et al., (2019), older subjects have benefit from an improved postural sway measurements following TrA training which included an abdominal draw-in maneuver. In agreement with the literature, neurological control was partially responsible to the positive changes and should be noted as another factor which improves core stability (other than actual muscular control).


This is important as some individuals may be able to reach a higher level of muscular activation, however will lack the proper muscle mass to provide enough force for trunk and pelvic stabilization, resulting in an inefficient postural control (Wirth et al., 2017). More athletic populations, such as football players, possess the adequate muscle mass to produce the amount of force required for their motor tasks. However, lack of optimal core strength may affect them to a similar scale; it is reasonable to expect a higher level of postural control and core stability in response to the rotational (resultant torque) forces and emphasis on the transverse plane for football players, particularly throwers; a study of well-trained elite football players revealed significant increases in muscle activation following specific core training of lateral and pronated planks (Roth et al., 2016). Sex differences are a consideration as well, with females presenting higher levels of rectus abdominis and external oblique activation during the same exercises. Interestingly, those are classified as global muscles, which may imply a higher level of neuromuscular control versus local muscles among females, as a future research question.


Core and injury rates

The association between core strength and injury rates has been studied in the literature through various methodologies. Common topics have included improper loading rates and reactions on the spinal cord as well as muscle strains (Raabe & Chaudhari, 2018). Core weakness, expressed in both he local and global musculatures, can impair balance control and lead to related injuries such as falling, which may be devastational at an elderly age (Szafraniec et al., 2018). With recreationally and competitive populations, core weakness can lead and is viewed by movement compensation patterns; Raabe & Chaudhari (2018) found significant compensations with the deep fascicles of the erector spinae (DES) among healthy adult runners using force plates and kinematics markers. The study established a correlation between weaker core musculature and movement compensations along the kinetic chain; running, as a repetitive sport with high levels of ground force loading, can therefore increase the risk for injuries when the core is inappropriately activated. A relative lack of core stability, distinct from core endurance, has been identified as a risk factor for several injuries in a systematic review by De Blaiser et al., (2018); lower levels of trunk isometric strength were associated with an increased risk for anterior cruciate ligament (ACL) injury, as well as reduced neuromuscular control of the core with tibial stress injuries. Both had a greater prevalence rate among female athletes, which stands in line with previous literature pointing sex differences with higher injury rates among females (Roth et al., 2016).


An interesting perspective from the Norwegian Olympic Federation members states that although impaired core stability is associated with injury risk, it should not be regarded in isolation; meaning, it can correlate to injury risk in conjunction with other biomechanics factors (Haugen et al., 2016).


Performance measures

The core is described through varied terminology in the literature. The global and local muscles are regularly being studied; however the span of the core region differs between studies. Szafraniec et al., (2018) portray the core from the anterior with the abdominals, posterior with the spinal area and glutes, superior with the diaphragm and inferior with the pelvic floor muscles. This definition can assist in setting kinetic checkpoint for performance measurements which apply to the core and its impact on performance. Several strength tests are in designated use for the core; the global trunk strength endurance test, maximal isometric strength testing and electromyography (which is not particular to the core, however is effective in measuring activation levels and firing rates) (Roth et al., 2016).


Other performance measures may focus on postural control, mentioned earlier in this discussion; for this, the level and velocity of postural sway may provide kinetic information regarding the impact of the core on one’s posture, where higher levels imply better core stability and related performance (Szafraniec et al., 2018). The effect of core training on performance is evaluated in a sport-specific manner; in football, for example, rotational strength of the trunk is a valuable measure for throwing purposes (Bayrakdar et al., 2020). In-direct performance measures, such as in the running biomechanics study by Raabe & Chaudhari, (2018), include quantifying compressive and shear forces on the spinal column using force plates and motion-caption markers, serving as a measurement for strength, or weakness, of the core as a supporting musculature.


Core exercises sample

Core exercises video link - click to see exercises




1. Primal roll with sit-up

· Cues for execution: lie pronated. Turn over unassisted to supine. Perform 1 sit-up. Roll over to pronated position and repeat.

· Scientific rationale: this exercise is a multi-planar dynamic core integration. It emphasizes motor control through rolling, a “primal movement pattern” (PMP). PMP is a set of several movements developed in the uterus and during infancy, with rolling sequences a major core stabilization tool (Nickelston, 2012). Poor biomechanics or inability to complete an unassisted roll can point a more foundational stability and mobility issues. The added sit-up is a progression and should be used for individuals who present adequate thoracic mobility as a pre-requisite for the added spinal flexion.


2. Ball pike-up

· Cues for execution: place feet on the ball in a pronated, full-arm plank position. Flex the hips while maintain neutral spine position. Return to start position and repeat.

· Scientific rationale: this exercise challenges the local stabilizers muscles by adding the exercise ball; the constant movement and shifting of the ball requires a higher level of local core stabilizers, including the ; transverse abdominis (TrA) and multifidus muscles. Activating those muscles can assist in reducing low back pain, as reported by Alhakami et al., (2019).


3. Plank

· Cues for execution: in a pronated position, place hands under shoulders fully extended and maintain isometric contraction. Reach forward, one arm at a time.

· Scientific rationale: the plank is a closed-chain, low-load exercise which activates the local core musculature. It was found to achieve a high level of maximum voluntary contraction through isometr4ic contraction, compared to sit-up and side planks (Oliva-Lozano & Muyor, 2020).



References

Alhakami, A. M., Davis, S., Qasheesh, M., Shaphe, A., & Chahal, A. (2019). Effects of McKenzie and stabilization exercises in reducing pain intensity and functional disability in individuals with nonspecific chronic low back pain: a systematic review. Journal of Physical Therapy Science, 31(7), 590-597.

Bayrakdar, a., Boz, h. k., & Işildar, ö. (2020). The Investigation of the Effect of Static and Dynamic Core Training on Performance on Football Players. Türk Spor ve Egzersiz Dergisi, 22(1), 87-95.

Biel, A., & Dorn, R. (2008). Trail guide to the body: How to locate muscles, bones and more. (5th edition). Books of Discovery.

Clark, M., & Lucett, S. (Eds.). (2010). NASM essentials of corrective exercise training. Lippincott Williams & Wilkins.

De Blaiser, C., Roosen, P., Willems, T., Danneels, L., Bossche, L. V., & De Ridder, R. (2018). Is core stability a risk factor for lower extremity injuries in an athletic population? A systematic review. Physical Therapy in Sport, 30, 48-56.

Ferraro, R., Garman, S., Taylor, R., Parrott, J. S., & Kadlowec, J. (2019). The effectiveness of transverse abdominis training on balance, postural sway and core muscle recruitment patterns: a pilot study comparison across age groups. Journal of Physical Therapy Science, 31(9), 729-737.

Haugen, T., Haugvad, L., Røstad, V., Lockie, R., & Sæterbakken, A. (2016). Effects of Core-Stability Training on Performance and Injuries in Competitive Athletes. Sportscience, 20.

Oliva-Lozano, J. M., & Muyor, J. M. (2020). Core muscle activity during physical fitness exercises: A systematic review. International Journal of Environmental Research And Public Health, 17(12), 4306.

Perry Nickelston, D. C., & FMS, S. (2012). Primal Rolling Patterns for Core Sequencing and Development. Dynamic Chiropractic Canada. 5 (10).

Raabe, M. E., & Chaudhari, A. M. (2018). Biomechanical consequences of running with deep core muscle weakness. Journal of Biomechanics, 67, 98-105.

Roth, R., Donath, L., Zahner, L., & Faude, O. (2016). Muscle activation and performance during trunk strength testing in high-level female and male football players. Journal of Applied Biomechanics, 32(3), 241-247.

Szafraniec, R., Barańska, J., & Kuczyński, M. (2018). Acute effects of core stability exercises on balance control. Acta of Bioengineering And Biomechanics, 20(3).

Wirth, K., Hartmann, H., Mickel, C., Szilvas, E., Keiner, M., & Sander, A. (2017). Core stability in athletes: a critical analysis of current guidelines. Sports Medicine, 47(3), 401-414.

Yamamoto, T., Smith, C. E., Suzuki, Y., Kiyono, K., Tanahashi, T., Sakoda, S., Morasso, P., & Nomura, T. (2015). Universal and individual characteristics of postural sway during quiet standing in healthy young adults. Physiological Reports, 3(3), e12329. https://doi.org/10.14814/phy2.12329

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