The core in general is a group of muscles that is important in providing support to the viscera as well as in providing stability to the spine which makes them the foundation of a healthy posture. In a way, it resembles a birdcage made up of muscles with the diaphragm serving as the roof, the abdominals as the front, paraspinal and gluteals in the back, and the pelvic floor and hip girdle musculature as the floor. 29 pairs of muscles make up this cage that helps to stabilize the spine, pelvis, and kinetic chain during functional movements. Without these muscles, the spine would be mechanically unstable when loaded with compressive forces. The core muscles work as a system in distributing forces and force generation with minimal compressive, translational, or shearing forces at the joints of the kinetic chain.
Muscles that are part of the core / Type of muscle fibers within the core muscles
The core muscle comprises of two types of muscle fibers: slow-twitch and fast-twitch. Slow-twitch fibers make up primarily the deep muscle layer (local muscle system) as these muscles are shorter in length, hence making them more suited for controlling intersegmental motion as well as responding to changes in posture and external loads. On the other hand, fast-twitch fibers primarily make up the superficial muscle layer (global muscle system). The structural characteristic of these fiber types (long and possess large lever arms) allows them to produce large amounts of torque and gross movements.
The abdominals have always been thought to be a vital component of the core. The transversus abdominis has received recognition numerous times in research for its stabilizing effects. Such effects may be attributed to the fact that most of its fibers run horizontally hence forming a natural belt around the abdomen. Abdominal hollowing or drawing the belly button inwards towards the spine has been noted to induce contraction/activation of the transversus abdominis. In healthy people, the transversus abdominis along with the multifidi have been shown to contract milliseconds before any observable movements of the upper and lower limbs. This finding proves the fact that it the abdominals have a major role in stabilizing the lumbar spine before any distal movement takes place. The same findings however cannot be found in patients with low back pain (LBP) as contractions of the transversus abdominis and multifidi were found to be delayed after limb movements.
The transversus abdominis works in sync with internal and external oblique to increase the intra-abdominal pressure which has been shown to impart stiffness to the spine hence inducing spinal stability. Additionally, the abdominals (and multifidi) are only required to engage 5%-10% of their maximal volitional contraction to induce the stiffening of the spinal segments.
As previously mentioned, the diaphragm serves as the roof of the muscular birdcage of the core while the pelvic floor serves as the floor. Compared to the abdominals and the paraspinal counterpart, the diaphragm and pelvic floor muscles have received much less recognition on their stabilizing function. This is primarily due to the lack of research on spinal stability for these two muscles. That being said, contraction of both diaphragm and pelvic floor muscles increases intra-abdominal pressure, thus adding to spinal stability. Recent findings have indicated that people with sacroiliac joint pain have impaired activation of the diaphragm and pelvic floor. Thus diaphragmatic breathing techniques and pelvic floor activation may be an important part of a core-strengthening program for spinal related conditions.
It has been known that hip musculature (mainly hip extensors & abductors) is important in maintaining good posture in standing and during gait. Consequently, lack of endurance and delayed firing of the gluteus maximus and medius muscles have previously been noted in people with LBP and other musculoskeletal conditions.
The role of the core in sports and exercise (how it can prevent injury) / Consequences of having a weak core
In general, core stability is pertinent in every movement that requires the spine to be stable. Common activities of daily living such as doing house chores are all made easier when the spine is stable allowing for reaching, lifting, and bending down movements. Good core stability would also relate to better posture and control which optimizes energy usage hence allowing someone to hold a posture for a longer duration (eg; long hours of sitting). Not to forget, good core stability improves standing balance, therefore, reducing the chances of slipping and falling down (especially important as a person ages).
Since the core is central to almost all kinetic chains of sports activities, Core stability is an important component maximizing efficient athletic function. A good balance of core strength, balance and motion will maximise all kinetic chains of upper and lower extremity function hence maximizing performance.
Good core stability allows the person to be in control of their body position, along with generating optimum power. Core stability is warranted in rotational movements which is a quality needed in almost every sport. From kicking a ball to swinging a racket, a person can optimize their power output by strengthening their core stabilizers. Additionally, having a good core strength would allow a person to hold body position for longer durations (eg; gymnastic & ballet routines).
Having good core stability is also pertinent to preventing injuries as poor core control induces compensatory patterns. A week core in relation to other body parts would force other muscles to overwork as in order to produce the desired force of movement. As an example, a hamstring strain may result from a delayed firing of the gluteus muscle, which has forced the hamstring to overwork more than it should.
Efficacy of Core strengthening for back pain/musculoskeletal conditions
There is adequate evidence that shows that individuals with chronic LBP and sacroiliac pain lack proper activation of core muscles and demonstrated the weakness of the core. Additionally, there has been evidence of increased fatigue, and reduction of paraspinal muscle size in patients with chronic LBP. Even high-performance athletes have been shown to have signs of core instability, which may increase their proneness to musculoskeletal injuries. In addition, a number of studies have found a correlation between susceptibility to knee injuries with the presence of core weakness in female athletes. Additional findings also highlight they lack the balance abilities to compensate for unexpected trunk perturbation.
That being said, in weak cores there tends to be an over activation of supporting superficial muscles in the absence of control and activation of the deep spinal core muscles. This compensatory pattern predisposes a person to further musculoskeletal injuries of the spine.
For the above reasons, a core strengthening program should be implemented for the treatment of LBP and the prevention of different musculoskeletal conditions. The efficacy of the core strengthening program in chronic LBP patients has been validated by previous studies. For example, a 6 weeks’ rehabilitation program which implemented core strengthening showed improvement in pain & function. Similarly, the implementation of a core strengthening program can be beneficial for musculoskeletal conditions other than LBP. This was shown by a study in 2019 in which they implemented a core strengthening program for patients with osteoarthritis of the knee and found improvements in pain & function at the end of 12 weeks.
How to train the core
There are 2 components of core strengthening: Stability & Strength. A training program should however start with a focus on stability before progressing to strength. This is due to the fact that injuries tend to happen when there is a lack of muscle coordination (proper firing/component of stability) rather than a lack of strength. Therefore, for the sake of injury prevention, and core training program should be initiated with coordination training before load/resistance is incorporated.
With that being said, a core strengthening program should be done in phases of gradual progression. The initial phase of training mainly revolves around learning to activate the abdominal wall at will, starting from deeper through to the superficial layer of the muscular wall. This includes the implementation of breathing techniques with hopes to engage both the diaphragm and pelvic floor muscles. Coordinated contraction of all deep and superficial layers of the muscular cage is needed for optimal spinal stabilization.
Exercises in standing should mirror functional movements. Balance & coordination should initially start within a wide base of support and progressively narrowed down to increase difficulty. Additionally, it can further be challenged by changing the surface via foam, rocker board, BOSU ball, etc.
From then on, training can progress towards incorporating movements of the limbs. These should be progressed from lying (isolated) to functional positions in sitting, standing & walking. Initial stages should focus on balance and coordination and addressed in all 3 cardinal planes; sagittal, frontal, and transverse. It should be noted that any exercise in standing with an emphasis on core stability should be preceded by abdominal bracing technique, to ensure proper activation of the core and avoid compensatory patterns. Functional training can be progressed by incorporating deceleration and dynamic stabilization via anti-rotational movements. Additionally, the elite level of core training should focus on the Unexpected Disturbance Program (UDP) and postural regulation via jumps, landings, and directional changes.
Myth in core strengthening.
In contrary to traditional belief, strengthening the core muscles does not have to be very heavy for it to be effective. As a matter of fact, the excessive load may predispose a person to a higher risk of injury. Additionally, the conventional method of using sit-ups as a means to increase core strength should be avoided as such a position puts a lot of compressive forces on the lumbar spine.
The core is the center of everything: every action relies on the capabilities of the core, the center of gravity follows the core, the transfer of power and energy depends on the core. As basic and as simple as it seems, there is more than meets the eye – it is more than “just a 6 pack”.